The expression profile of the <Emphasis Type="Italic">Tuber borchii</Emphasis> nitrite reductase suggests its positive contribution to host plant nitrogen nutrition |
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Authors: | M Guescini S Zeppa R Pierleoni D Sisti L Stocchi V Stocchi |
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Institution: | (1) Institute of Biological Chemistry “G. Fornaini”, University of Urbino “Carlo Bo”, Via Saffi, 2, 61029 Urbino (PU), Italy;(2) Istituto di Ricerca sull’Attività Motoria, Università degli Studi di Urbino “Carlo Bo”, via Sasso 75/G, 61029 Urbino (PU), Italy;(3) Istituto e Orto Botanico, Università degli Studi di Urbino “Carlo Bo”, Via Bramante, 28, 61029 Urbino (PU), Italy |
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Abstract: | Ectomycorrhizal symbiosis is a ubiquitous association between plant roots and numerous fungal species. One of the main aspects of the ectomycorrhizal association are the regulation mechanisms of fungal genes involved in nitrogen acquisition. We report on the genomic organisation of the nitrate gene cluster and functional regulation of tbnir1, the nitrite reductase gene of the ectomycorrhizal ascomycete Tuber borchii. The sequence data demonstrate that clustering also occurs in this ectomycorrhizal fungus. Within the TBNIR1 protein sequence, we identified three functional domains at conserved positions: the FAD box, the NADPH box and the two (Fe/S)-siroheme binding site signatures. We demonstrated that tbnir1 presents an expression pattern comparable to that of nitrate transporter. In fact, we found a strong down-regulation in the presence of primary nitrogen sources and a marked tbnir1 mRNA accumulation following transfer to either nitrate or nitrogen limited conditions. The real-time PCR assays of tbnir1 and nitrate transporter revealed that both nitrate transporter and nitrite reductase expression levels are about 15-fold and 10-fold higher in ectomycorrhizal tissues than in control mycelia, respectively. The results reported herein suggest that the symbiotic fungus Tuber borchii contributes to improving the host plant’s ability to make use of nitrate/nitrite in its nitrogen nutrition. |
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Keywords: | Tuber borchii Ectomycorrhizae Expression regulation Nitrate assimilation Nitrogen limitation |
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