Molecular and functional characterization of the NAC transfactor family from soybean (Glycine max) / Caracterização molecular e funcional de transfatores da família NAC de soja (Glycine max)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The identification of cell signaling pathways in response to different stresses has become a major focus for understanding the molecular bases of plantenvironment interactions. We have previously identified a set of soybean genes co-regulated by ER- and osmotic stresses, which possibly constitute a novel integrative pathway in plants. Among the identified genes, GmATAF2 and GmNAM encode transcription factors from the NAC-family, whose representatives are involved in events of plant development and response to biotic and abiotic stresses. In this study, we demonstrated that the ESTs of GmATAF2 and GmNAM correspond to different regions of the same gene, homologous to Arabidopsis ATAF1 and ATAF2 and named GmATAF. Furthermore, GmATAF transient expression in soybean protoplasts resulted in the repression of the integrative genes and genes specifically induced by dehydration and ER stress, suggesting that GmATAF is a repressor of different stress-responsive pathways in soybean. Given the potential of NAC transfactors as targets for strategies of engineered resistance, in addition to GmATAF, we isolated and characterized other 6 soybean NAC genes (GmNAC1- GmNAC6). The 7 GmNAC genes could be phylogenetically separated into 6 subgroups: ATAF1, ATAF2, NAP, ANAC, NAM and TERN, possibly representing non-redundant NAC genes. Transient expression experiments in tobacco plants revealed that all GmNAC proteins were located in the nucleus, consistent with their roles as transcription factors. Moreover, GmNAC2, GmNAC3 and GmNAC5 proteins exhibited transcriptional activity in yeast. Consistent with a functional diversity suggested by the phylogenetic analysis, the GmNAC genes displayed a differential expression pattern in soybean organs. Using transgenic plants defective for the unfolded protein response (UPR) activation, we demonstrated that activation of GmATAF, GmNAC2 and GmNAC6 genes occurs via an ER-stress signaling pathway distinct from the UPR. The NAC soybean genes are also involved in the response to other abiotic stresses. We demonstrated that GmATAF, GmNAC2, GmNAC3 and GmNAC4 are strongly induced by osmotic stress, though possibly through different pathways. While GmNAC3 and GmNAC4 are also induced by the hormone ABA, the induction of GmATAF and GmNAC2 during osmotic stress seems to be ABA-independent. GmNAC3 and GmNAC4 are also induced by salinity and jasmonic acid, but not by low temperatures. Consistent with an involvement in cell death programs, GmATAF, GmNAC1 and GmNAC6 genes were up-regulated by cell death inducers and repressed by senescence inhibitors. Furthermore, the transient expression of GmNAC1, GmNAC5 and GmNAC6 in tobacco leaves resulted in cell death and enhanced the expression of the senescence gene marker CP1. Gene expression analysis of senescent soybean leaves suggests that GmNAC1 is associated with senescence progression, while GmNAC5 and GmNAC6 is more likely to be involved in other forms of cell death, such as embryo development-induced cell death and the hypersensitive response. Collectively, these results indicate that the characterized NAC genes consist of transcription factors involved in response to different abiotic stresses and take part in cell death events in soybean.

ASSUNTO(S)

soja regulação de expressão gênica gene expression regulation soybean efeito do stress stress effect biologia molecular

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