Plastid inheritance in Oenothera: paternal input may influence transmission patterns

Summary Prior genetic analysis of Oenothera to assess the mechanism(s) controlling differential (biparental) plastid transmission patterns have indicated that the plastome plays an integral role. However, the influence of putative variation in paternal plastid input remains unclear. Pollen collected from Oenothera hookeri plants containing one of four different plastome types (I–IV) in a constant nuclear background (A₁A₁) was examined cytologically by DAPI/ epifluorescence microscopy. The number of plastid DNA aggregates per pollen generative cell was found to differ significantly. Plants containing plastome types I or II displayed an average of about ten plastid DNA aggregates per generative cell whereas plants containing types III or IV displayed, on average, 15 plastid DNA aggregates. The potential paternal plastid contribution to the egg cell at syngamy (III=IV>I=II) differs from the previously determined survival frequencies of the same four plastid types (I>III>II>IV) progeny.Scientific article no. A-5036, contribution no. 8084 of the Maryland Agricultural Experimental Station     

Plastid inheritance in Epilobium

Summary Interspecific hybrids of various Epilobium species have been produced in order to analyse plastid inheritance using restriction fragment polymorphisms of plastid DNA as markers. This analysis reveals that interspecific hybrids exhibit only the fragment pattern of the maternal plastome. Southern hybridization experiments using cloned species-specific plastid DNA fragments as markers confirm the maternal type of plastid inheritance in Epilobium, while providing at least a tenfold increase of sensitivity to detect restriction polymorphisms. Within the limit of detection even young seedlings contain no plastid DNA from the paternal parent. However, investigations of plastomes of large populations have provided evidence that a very low frequency of paternal plastid transmission can occur. Thus, the mechanism which ensures the elimination of paternal plastids is not 100% efficient. This suggestion is also supported by intraspecific reciprocal crosses between plants carrying mutant white and normal green plastids. While the offspring usually exhibit the maternal plastid type, a few cases indicate an apparent paternal plastid transmission.Abbreviations kbp kilobase pairs - ptDNA plastid DNA     

Plastid inheritance in Oenothera: organelle genome modifies the extent of biparental plastid transmission

Summary The transmission abilities of four out of the five major plastome types of Oenothera (I–V) were analyzed in a constant nuclear background by assessing both the frequency of biparental inheritance and the extent of variegation in the progeny. Reciprocal crosses were performed between plants carrying one of four wild-type plastomes and plants carrying one of seven white plastid mutants. The frequency of biparental plastid transmission ranged from 0 to 56% depending on the plastid types involved in the crosses. The transmission abilities of the four representative wild-type plastids appear to be in the order of I > III > II > IV in the nuclear background of O. hookeri str. Johansen. In general, variegated seedlings from crosses that produced a higher frequency of biparental plastid transmission also had an increased abundance of tissue containing plastids of paternal origin. Although the transmission abilities of most Oenothera plastid mutants are comparable to the wild-type plastids, three mutant plastids derived from species having different type I plastids show three distinguishable transmission patterns. This study confirms the significant role of the plastome in the process of plastid transmission and possibly in plastid multiplication. However, the hypothesis of differential plastid multiplication rates suggested by earlier studies can explain the results only partially. The initiation of plastid multiplication within the newly formed zygote also seems to be plastome-dependent.     

Physical evidence for recombination of chloroplast dna in hybrid progeny of Chlamydomonas eugametos and C. moewusii

Summary Differences in the restriction endonuclease fragmentation patterns of chloroplast DNA (cpDNA) from C. eugametos and C. moewusii have been used to study the inheritance of these DNAs in interspecific hybrids. Analysis of the cpDNAs from ten randomly selected F₁ hybrids, in each case revealed cpDNA to be recombinant for AvaI and BstEII restriction sites, although fragments characteristic of C. eugametos, the mt+ parent, were typically found in excess of those for C. moewusii, the mt– parent. In backcrosses between an F ₁ mt+ hybrid and C. moewusii mt–, seven randomly selected B₁ hybrids showed cpDNA restriction patterns either identical to or highly similar to that of the mt+ parent. We propose that cpDNA molecules are predominantly transmitted by the mt+ parent in both F₁ and B₁ generations but that selection favors survival of F₁ progeny with recombinant chloroplast genomes which avoid interspecific incompatibilities. On the surface, the inheritance of recombinant cpDNA contrasts with the simultaneous uniparental inheritance of two putative chloroplast markers (sr-2 and er-nM1 ⁺). However, it may be that these two markers are by chance associated with cpDNA sequences of the mt+ parent which were selected in all F₁ hybrids.     

Cultivar variability for the presence of plastid DNA in pollen of Pisum sativum L.: implications for plastid transmission

Summary The mode of plastid transmission in the garden pea (Pisum sativum L.) was analyzed cytologically using the DNA-fluorochrome 4,6-diamidino-2-phenylindole (DAPI) in conjunction with epifluorescence microscopy. The reproductive cells of mature pollen obtained from 12 inbred lines and cv Early Alaska were examined for the presence or absence of DAPI-stained plastid DNA aggregates. Plastid DNA was detected in all 13 pea lines examined, although there was variability with regard to the percentage of pollen graines showing plastid DNA aggregates of generative cells (ranging from 3% in accession 82-12r to 65% in accession 82-14n). These cytological results may indicate genetic variability for plastic DNA inheritance in the garden pea. This paper is dedicated to the memory of Gerald A. Marx     

Plastid DNA is not detectable in the male gametes and pollen tubes of an angiosperm (Antirrhinum majus) that is maternal for plastid inheritance

Summary Prior cytological observations using DAPI/epifluorescence microscopy have suggested that the method could be used to rapidly screen plant species for their potential mode of plastid DNA transmission. Cytoplasmic DAPI-DNA aggregates were observed in generative cells of germinated pollen of Medicago sativa (alfalfa), a species known genetically to display biparental transmission, but not in Antirrhinum majus (snapdragon), a species known to be maternal for plastid transmission. If, as suggested, these aggregates are plastid DNA nucleoids, then M. sativa pollen should contain plastid DNA detectable by molecular biology methods and A. majus pollen should not. Total DNA was isolated from germinated pollen and analyzed by Southern blot hybridization. A clone containing part of the rbcL gene from the garden pea plastome was used as a probe for plastid DNA. This probe hybridized with a restriction fragment from M. sativa pollen DNA, but not detectably with A. majus pollen DNA, thereby corroborating the identification of the cytoplasmic DAPI-DNA aggregates in M. sativa pollen as plastid DNA, and confirming the cytologically determined absence of plastic DNA in A. majus pollen.     

Non-Mendelian and skewed segregation of DNA markers in wide crosses of the bean rust fungus,Uromyces appendiculatus

The inheritance of DNA markers was investigated in 27 F₂ progeny from a single F₁ hybrid derived from a wide cross inUromyces appendiculatus. This cross was unusual because asexual spores were used to fertilize sexual fruiting structures. Sixty percent of the DNA markers failed to segregate according to simple Mendelian ratios. Segregation bias was evident, in that F₂ progeny inherited on average 91 % of maternal bands and 52% of paternal bands, which deviates significantly from the expected value for each of 75% for dominant markers. Because of these distortions, linkage mapping was not possible with this population. Evaluation of two F₁s from a second wide cross, reciprocals obtained by normal fertilization, also showed non-Mendelian inheritance of one of three co-dominant RFLPs and five of six isozyme markers, indicating that the method of crossing was probably not responsible for the abnormal segregation patterns in the first cross. Either genetic incompatibility, similar to that of an interspecific cross, or selection of particular genotypes could explain the genetic anomalies reported here.     

Non-random plastid segregation in somatic hybrids of Datura innoxia with several other Solanaceous species

Summary A non-random plastid segregation was found in somatic hybrids of Datura innoxia with seven different Solanaceous species. 14 out of 17 examined somatic hybrids showed the plastid features of Datura innoxia. Within the limits of sensitivity of the applied methods, one line could be shown to contain mixed plastids. Since sexual offspring of this line contains only one set of plastids, it is assumed that this is probably a periclinal chimaera due to the plastome, i.e., the plastid mixture is present on a plant rather than a cell level.     

DNA markers define plastid haplotypes in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

To identify genetic markers in the Arabidopsis thaliana plastid genome (ptDNA), we amplified and sequenced the rpl2-psbA and rbcL-accD regions in 26 ecotypes. The two regions contained eight polymorphic sites including five insertions and/or deletions (indels) involving changes in the length of A or T mononucleotide repeats and three base substitutions. The 27 alleles defined 15 plastid haplotypes, providing a practical set of ptDNA markers for the Columbia, Landsberg erecta and Wassilewskija ecotypes that are commonly used in genetic studies and also for the C24 and RLD ecotypes that are the most amenable for cell culture manipulations.     

Optional elements in the chloroplast DNAs of Chlamydomonas eugametos and C. moewusii: unidirectional gene conversion and co-conversion of adjacent markers in high-viability crossses

Unlike most polymorphic markers in the Chlamydomonas eugametos and Chlamydomonas moewusii chloroplast DNAs (cpDNAs), the C. moewusii 6- and 21-kb extra sequences and the C. eugametos-specific CeLSU ⋅ 5 intron are transmitted to all of the few viable progeny in reciprocal crosses between the two green algae. To determine whether this unidirectional transmission pattern is due to gene conversion or to selection for F1 hybrid survival, we followed the inheritance of the parental alleles at the loci featuring these three deletions/additions and at several other polymorphic cpDNA loci in zygospore clones derived from high-viability crosses. The great majority of the zygospore clones examined inherited exclusively the long alleles from the mt ^– parent at the loci containing the three optional cpDNA elements, but as expected, they preferentially inherited the markers from the mt ⁺ parent at most other loci. Our results therefore indicate that all three optional cpDNA sequences propagate themselves very efficiently by gene conversion in crosses between strains differing by the presence of these elements. The co-conversion tracts associated with these sequences are longer (>3 kb) than those previously reported for mobile elements spreading by gene conversion. Our results also revealed that less efficient gene conversion events occurred at two other cpDNA loci. Received: 12 February / 14 May 1996     

Light and benzylaminopurine induce changes in ultrastructure and gene expression in plastids of Petunia hybrida cell cultures

Summary The regulatory effect of light and the cytokinin 6-benzylaminopurine (BA) on the plastid ultrastructure and plastid DNA gene expression is studied in white and mutant green cell suspension cultures of Petunia hybrida. By electron microscopy we show that both light and 6-benzylaminopurine induce the formation of thylakoid membranes and grana structures in plastids of the green cultures. For membrane formation in plastids of white cultures, light in combination with BA is required. Light and benzylaminopurine also influence the plastid DNA gene expression. By in-organello protein synthesis with isolated plastids we show that light as well as benzylaminopurine affects the synthesis of plastid DNA encoded proteins. A characteristic effect of benzylaminopurine on plastids from white and green cultures is the reduction in the synthesis of the CFI subunits of 55,000 and 57,000 D, and the reduction in the synthesis of large polypeptides with a molecular weight higher than 67,000 D. In contrast to benzylaminopurine, light only affects the DNA gene expression of plastids from white cell cultures, that are in a very early stage of plastid development. Light stimulates the synthesis of polypeptides with a molecular weight of 84,000, 70,000 and 46,000 D which are encoded by cpDNA in these white culture plastids. In green cell cultures both plastids with a etioplast-like phenotype and with a chloroplast like morphology synthesize similar polypeptides, resulting in the same polypeptide pattern. Our results indicate that qualitative differences in plastid DNA gene expression as an effect of light do occur but only in plastids at very early stages of chloroplast development. We observe a gradual reduction in the number of high molecular weight polypeptides at later stages of chloroplast development. This suggests that these large polypeptides are characteristic for plastids at an early developmental stage.Abbreviations LSU of RuBPCase large subunit of Ribulose-1, 5-bisphosphate carboxylase - CF₁ coupling factor of the ATPase complex - LCH chlorophyll a/b protein - BA 6-benzylaminopurine - cpDNA chloroplast DNA     

Maternal inheritance of chloroplasts in the horsetail Equisetum variegatum (Schleich.)

Reliable data concerning the transmission of chloroplasts in the Pteridophyta are needed both for phylogenies based on chloroplast DNA (cpDNA) sequences and in order to study the evolution of this trait in conjunction with the evolution of the life cycle and the sexual reproduction of land plants. For the first time, this paper describes organelle transmission in the division Sphenophyta, represented by the extant genus Equisetum. By following the fate of polymorphic cpDNA during three intraspecific reciprocal crosses we found no trace of paternal transmission in Equisetum variegatum. The seemingly strict maternal transmission of cpDNA in this species suggests that uniparental chloroplast inheritance preceded the evolution of heterospory in the seed-plant lineage. Received: 16 July / 5 October 1999     

Heterosis of adult mouse (Mus musculus) ultrasonic vocalizing

Four sets of adult mice (Mus musculus), each comprised of individuals from two inbred strains and both reciprocal F₁ crosses, were tested during male-female and female-female dyadic encounters for their emission of 70-kHz ultrasonic vocalizations. For each sex-dyad type of each set, a single progeny mean representing both reciprocal F₁ groups was calculated and compared to (1) the average value from the inbred parents and (2) the higher mean of the within-set progenitor inbred strains. In addition to demonstrating strain-and sex-influenced ultrasonic vocalizing levels, the results indicated that for each set examined, the F₁-progeny mean amount of ultrasonic vocalizing significantly exceeded the average inbred parent value. This was true for both dyad types, providing strong evidence that ultrasonic vocalizing displlays a directional dominance mode of inheritance in both female and male mice. Moreover, for female-female dyads of all four sets and for male-female dyads of three of four sets, the F₁-progeny mean amount of ultrasonic vocalizing significantly exceeded that of the highest progenitor inbred strain. Analyses of ultrasonic vocalizing latencies yielded similar hybrid-inbred differences. Collectively, these findings are interpreted as being consistent with the notion that, for both sexes of mice, ultrasonic vocalizing is a phenotypically heterotic behavioral trait.This research was supported, in part, by a Florida State University Psychobiology Fellowship awarded to J.C.M. and by NINCDS Grant NS 15560.     

Autosomal and maternal effects on pupation behavior inDrosophila melanogaster

This study demonstrates the importance of using a complete set of 16 reciprocal crosses (F₁, backcrosses, and F₂) to thoroughly investigate both genetic and nongenetic influences on patterns of inheritance of larval pupation behavior inDrosophila melanogaster. Larvae derived from natural populations show significant variation in pupal height, defined as the distance a larva pupates above the feeding substrate. Differences in the distance a larva pupates from fruit in nature is known to affect the fitness ofDrosophila populations. In this study the heredity of pupal height is analyzed by performing crosses between high- and low-pupating strains. We found that the inheritance of pupal height fit a classical additive polygenic model of inheritance, with intermediate F₁ pupal heights and greater variances in the F₂ generation. In addition, a significant maternal effect was also found by analyzing the reciprocal backcrosses. Progeny with low-pupating mothers had lower pupation heights than those with low-pupating fathers. Similarly, progeny with high-pupating mothers tended to have higher pupal heights than those with high-pupating fathers. This maternal effect was not attributable to strain differences in permanent cytoplasmic factors, sex chromosomes, or developmental time. Finally, we speculate upon the environmental conditions under which a transient maternal effect on pupation behavior would be expected to evolve in natural populations.This work was supported by a University Research Fellowship and Operating Grant from the Natural Sciences and Engineering Research Council to M. B. Sokolowski. S. J. Bauer was the recipient of an Ontario Graduate Scholarship.     

Loss of mt +-derived zygotic chloropiast DNA is associated with a lethal allele in Chlamydomonas monoica

Summary The Chlamydomonas monoica mutant allele mtl-1, is associated with the formation of nonviable zygospores following self-mating of the mutant strain. Furthermore, mtl-1 heterozygote populations show a 50% reduction in germination frequency and no transmission of a chloroplast antibiotic resistance marker carried by the mtl-1 parent. To determine whether the effects on zygospore viability and chloroplast gene transmission resulted from the direct involvement of the mtl-1 locus in the control of mt ⁺-directed uniparental inheritance of chloroplast DNA (cpDNA), we have used the DNA-specific fluorochrome DAPI to follow the fate of cpDNA during the maturation of zygotes. Throughout the first few hours after the initial fusion of gametes, the young zygotes show DAPI-fluorescent nucleoids distributed symmetrically around the region of nuclear fusion, and presumably located within both of the parental chloroplasts. Wild-type and mtl-1 mutant zygotes show similar early staining patterns. As the zygotes age, the staining patterns become asymmetric for the wildtype population, with all of the visible cytoplasmic nucleoids restricted to one side of the zygote. In contrast, mtl-1 homozygotes appear to lose cytoplasmic nucleoids from both sides of the zygote simultaneously and within 24 h are apparently devoid of cpDNA. By introducing a mutation which arrests cell fusion (and prevents plastid fusion), we can show that (1) the asymmetric nucleoid distribution in wildtype zygotes results from the loss of nucleoids from one gamete in each mating event, and (2) the additional loss of cpDNA in mtl-1 homozygotes does not require contact between parental plastids (thus the nuclease responsible for cpDNA degradation is not sequestered within the chloroplast of one gamete). We propose that the mtl-1 mutant strain is defective for a process which normally protects cpDNA of mt ⁺ origin.     

Changes in chloroplast genome composition and recombination during the maturation of zygospores of Chlamydomonas reinhardtii

Summary In crosses of the unicellular green alga Chlamydomonas reinhardtii, the chloroplast genes are normally transmitted exclusively by the maternal parent to zygospore progeny. However, transmission of the paternal chloroplast alleles can be increased markedly by certain pretreatments of the maternal parent prior to mating. As zygospores age prior to induction of meiosis, they display decreased biparental transmission of chloroplast alleles and increased transmission of chloroplast alleles from only the maternal or paternal parent. In this report, chloroplast genome composition of biparental zygospores is shown to change in several ways during zygospore maturation. Allelic ratios of chloroplast genes within biparental zygospore clones become maternally or paternally skewed as the zygospores age, cotransmission of chloroplast alleles is reduced, and recombination increases, resulting in an expansion of genetic map distances between chloroplast markers used in this cross. The recovery of unequal frequencies of zygospore progeny expressing reciprocal recombinant genotypes confirms and extends other reports of the predominance of nonreciprocal recombination in organelle genetic systems.     

Maternal transmission of mitochondrial DNA in interspecific hybrids of Populus

Summary Restriction fragment analysis was conducted to investigate the mode of inheritance of mitochondrial (mt) DNA in F₁ progeny of two P. deltoides x P. deltoides, three P. deltoides x P. nigra, and two P. deltoides x P. maximowiczii controlled crosses, and in Populus x canadensis by using 16 restriction endonucleases and two heterologous probes of cloned mtDNA fragments of maize. Five restriction fragment length polymorphisms (RFLPs) of mtDNA differentiated P. deltoides from P. nigra, whereas three RFLPs of mtDNA separated P. deltoides from P. maximowiczii. In all cases, F₁ progeny of P. deltoides x P. nigra, and P. deltoides x P. maximowiczii, crosses had mtDNA restriction fragments of only their maternal P. deltoides parents. P. x canadensis had mtDNA restriction fragments of only P. deltoides. F₁ progeny of intraspecific P. deltoides crosses also had the same mtDNA fragments as their maternal parent. The results clearly demonstrate uniparental-maternal inheritance of the mitochondrial genome in F₁ interspecific hybrids of P. deltoides with P. nigra and P. maximowiczii.     

Genes for components of the chloroplast translational apparatus are conserved in the reduced 73-kb plastid DNA of the nonphotosynthetic euglenoid flagellate Astasia longa

The colourless, nonphotosynthetic protist Astasia longa is phylogenetically related to Euglena gracilis. The 73-kb plastid DNA (ptDNA) of A. longa is about half the size of most chloroplast DNAs (cpDNAs). More than 38 kb of the Astasia ptDNA sequence has been determined. No genes for photosynthetic function have been found except for rbcL. Identified genes include rpoB, tufA, and genes coding for three rRNAs, 17 tRNAs, and 13 ribosomal proteins. Not only is the nucleotide sequence of these genes highly conserved between A. longa and E. gracilis, but a number of these genes are clustered in a similar fashion and have introns in the same positions in both species. The results further support the idea that photosynthetic genes normally encoded in cpDNA have been preferentially lost in Astasia, but that the chloroplast genes coding for components of the plastid translational apparatus have been maintained. This apparatus might be needed for the expression of rbcL and also for that of still unidentified nonphotosynthetic genes of Astasia ptDNA.These sequence data will appear in the EMBL/Gen Bank/DDBJ nucleotide sequence data base under accession numbers X75651, X75652 and X75653     

Cell type determines plastid transmission in tomato intergeneric somatic hybrids

Summary Mesophyll (M)- and suspension culture (S)-derived protoplasts of both Lycopersicon esculentum, tomato, and its wild relative Solanum lycopersicoides were fused as S+M, M+M and S+S combinations, respectively, to resolve the role of parental cell types in determining cpDNA transmission to intergeneric somatic hybrid plants. The mesophyll cpDNA was preferentially transmitted to 96% of the plants, each regenerated from a separate callus, in M+S and S+M fusion combinations. In contrast, for the M+M combination there was an equable distribution of either tomato cpDNA or that of S. lycopersicoides among the 34 hybrid plants. The number of plastids or proplastids in mesophyll or suspension protoplasts was not a factor regulating cpDNA transmission. Mesophyll or suspension protoplasts of both fusion partners had comparable frequencies of either plastid type with a mean of 23. The biased transmission of plastids from the mesophyll parent in somatic hybrid plants of S+M and M+S combinations appears to be due to differential multiplication of plastids, possibly conditioned by an unequal input of the nucleoids found in plastids versus proplastids. In the M+M fusion, plastid and nucleotid input and subsequent plastid multiplication are apparently equal, and when combined with random sorting out leads to an equal distribution of parental cpDNAs in the regenerated somatic hybrid plants. For the S+S combination, 22 somatic hybrid plants have exclusively tomato cpDNA, an outcome that is not readily explained by donor cell input.     

Inheritance of morphine sensitivity in (WAG/G-fischer-344) F1 rats

The effects of morphine on the pain sensitivity and motor activity of progeny obtained by different variants of crossing purestrain WAG/G and Fischer-344 rats are studied. Four groups of rats were investigated: WAG/G (male and female WAG/G rats were crossed), Fischer-344 (Fischer-344 male and female), F/W (Fischer-344 male, WAG/ G female) F₁ hybrids, and W/F (WAG/G male, Fischer-344 female) F₁ hybrids. It is shown that the inheritance of individual features of sensitivity to the analgetic effect of morphine as well as of pain sensitivity is apparently sex-linked. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 120, N ^o 9, pp. 291–293, September, 1995 Presented by V. N. Yarygin, Member of the Russian Academy of Medical Sciences