The Functional Analysis Of Stress Resistence Genes TaNAC3 And TaSIRT6

Plants have evolved complicated signaling transduction mechanisms to orchestrate the response to drought stress. As a crucial stress responsive phytohormone, ABA is vastly produced under drought, and therefore triggers ABA-dependent signaling pathway to enhance drought tolerance. Plant-specific NAC transcription factors modulate the resistance to abiotic stress, however their involvement specific to drought tolerance has not been widely reported. On the other hand, abiotic stress commonly accelerates early senescence. NAD+-dependent deacetylase SIRTUIN had been found to participate into senescence in yeast and animals, but its role in plans has not been documented.Our lab bred a wheat introgression cultivar SR3 with superior salt and drought tolerance capacity via the asymmetric somatic hybridization method. In this study, we studied the function of a wheat NAC transcription factor TaNAC3, and found that it specifically offered drought tolerance via promoting ABA pathway. Furthermore, we isolated three transcripts of NAD+-dependent deacetylase TaSIRT6 from SR3, and primarily confirmed their role in plant senescence.1. The specific contribution of a wheat NAC transcription factor TaNAC3 to drought toleranceIn the previous work of our laboratory, a wheat NAC transcription factor TaNAC3 had been identified, and its heterogeneous overexpression Arabidopsis lines had been constructed. In this work, we found TaNAC3 was induced by PEG treatment, suggesting its putative role in the response to drought. TaNAC3 was localized in both nucleus and cytoplasm, and exogenous ABA treatment promoted its transfer into the nucleus. TaNAC3 overexpression enhanced drought tolerance in Arabidopsis. In comparison with the wildtype, TaNAC3 overexpression lines showed similar phenotype, but exhibited lower water loss rate. This suggesting TaNAC3 offered drought tolerance via lowering transpiration rate by accelerating stomatal closure rather than via modulating the water absorption capacity of roots.Drought commonly induces the over-production of ABA, which promotes stomatal closure, reduces transpiration rate, and consequently lessens water loss. Our results showed that TaNAC3 overexpression elevated the sensitivity to ABA, and improved the expression of some genes playing key roles in ABA synthesis and ABA-dependent stress responsive signaling transduction pathways, indicating that TaNAC3 may enhance drought tolerance via accelerating ABA pathway. Sequence analysis showed that there had NAC transcription factor binding cis-elements in the promoters of several genes that were regulated by TaNAC3, implying some of these gene may be the target genes of TaNAC3. To confirm this speculation, we constructed some plastids for yeast one hybridization, and TaNAC3 was produced in E. coli, which could be used for the assay of the binding of TaNAC3 to promoters of above ABA pathway associated genes. One the other hand, we isolated the promoter of TaNAC3, in which ABA responsive element ABRE and drought responsive MYB transcription factor binding element MYB were present. In line with these data, we speculate that drought and ABA induces the expression of TaNAC3, and the induction of TaNAC3 in turn elevates ABA pathway, which forms a signaling amplification circuit to enhance drought tolerance.2. Wheat NAD+-dependent histone deacetylase TaSIRT6 delayed plant senescenceTo know the role of NAD+-dependent deacetylase (Sirtuin) in plant senescence, we isolated three copies of wheat sirtuin gene TaSIRT6, namely SIRT6-1, SIRT6-2 and SIRT6-3, from SR3. These three copies shared high identity to yeast Sir2 and mammalian SIRT6. There had some SNP and Indels among three copies, resulting in the difference in peptide size and amino acid polymorphism. Similar to mammalian SIRT6, TaSIRT6 were localized in the nucleus; however, TaSIRT6-2 was also detected in the cytoplasm. The overexpression of TaSIRT6-1 and TaSIRT6-2 did not alter the effect of NaCl and other treatment on growth of Arabidopsis seedlings. In comparison with the wild-type, the senescence of TaSIRT6-1 and TaSIRT6-2 overexpressors was obviously delayed, and in the dark, the leaves of their seedlings were weakly etiolated. The overexpression of TaSIRT6-1 and TaSIRT6-2 significantly reduced the expression of senescence associated genes SEN4, SAG12, SAG18, SAG20, and the reduction of SEN4 and SAG12 was up to 1000 fold. These results show that TaSIRT6 plays an important role in the aging process in plants.