Functional Analysis Of Two Transfactors GmNAC2and Gmnac5in Soybean

The NAC (NAM, ATAF1,2, CUC2) family proteins are one of the largest plant-specific families of transcription factors which comprise several sub-families, such as ATAF, NAP and NAM. NAC (NAM, ATAF1,2, and CUC2) proteins have regulatory activity, transcription regulation and resistance to stress in plant development. NAC genes may be induced by developmental events or multiple environmental factors. The research of NAC transcription factors of soybean (Glycine max (L.) Merr.) has developed only5years, so the regulation mechanism of most NAC proteins in soybean is not clear. Here we report functions of GmNAC2and GmNAC5to serve theory basis for genetic improvement of soybean quality.GmNAC2(Glycine max NAC like gene2) is the first ATAF-like NAC identified transcription factor in soybean. The ATAF genes are involved in response to a variety of abiotic stresses, such as drought, cold and salinity. The soybean organ expression patterns of the gene were examined, and GmNAC2was highly expressed in the roots and immature embryos, especially strongly in immature embryo of40days after flowering. We found GmNAC2was induced by JA, mechanical wounding, high salinity, drought, and cold treatments, especially it was strongly affected by drought stress, but was not induced by ABA. The result suggests that up-regulation of GmNAC2by drought, salinity and cold may be not dependent on ABA.To analyze regulatory effect of GmNAC2gene under abiotic stresses, the transgenic tobacco and hairy root of GmNAC2gene were used for further study. We found GmNAC2overexpression tobacco lines were hypersensitive to drought, high salinity, and cold stress. MDA content of transgenic tobacco was higher than CK under abiotic stresses while O2and H2O2(ROS) contents of transgenic tobacco were also higher than CK after stress treatments. GmNAC2overexpression hairy roots reduces SOD activities and APX activities under drought, salt and cold stress, and GmNAC2silencing hairy roots enhances SOD activities and APX activities under drought stress, salt stress and cold stress conditions. The results demonstrate the great potential of this gene to reduce the ROS-scavenging ability and stress tolerance of crops.To further elucidate the mechanism of GmNAC2-mediated tolerance, we performed transcriptome analyses comparing GmNAC2overexpression tobacco with wild type tobacco leaves under normal conditions. We identified interesting down-regulated genes such as related to ROS-scavenging in GmNAC2overexpression tobacco. The down-regulated genes related to ROS-scavenging include genes coding thioredoxin, SOD enzyme, peroxiredoxin proteins. Collectively, GmNAC2may function as a negative regulator in drought, high salinity, and cold stress signaling pathways through modulation of ROS-scavenging genes expression.GmNAC5(Glycine max NAC like gene5) is a member of NAM subfamily belonging to NAC transcription factor in soybean. To date, the documents about NAM transcription factors showed that NAM subfamily members often maintained SAM development. The soybean organ expression patterns of the gene were examined, and GmNAC5gene was highly expressed in the roots and immature embryos, especially strongly in immature embryo of40days after flowering. We found GmNAC5was induced by mechanical wounding, high salinity and cold treatments, but was not induced by ABA. The results suggest GmNAC5may have regulatory effect in abiotic stresses response. GmNAC5overexpression transgenic tobacco plants have GmNAC5gene expression tested by qPCR. Analysis the leaves growth of transgenic plants and CK we found leaves of GmNAC5overexpression tobacco were narrower than CK tobacco. We first got GmNAC5overexpression transgenic soybean plants with about10times GmNAC5overexpression in leaves. Analyze the plant type of transgenic soybean, we found some T1generation plants had more lateral shoots.