| Authors: | Zhu, Y., Wu, N., Song, W., Yin, G., Qin, Y., Yan, Y., Hu, Y. |
| Abstract: | MYB-type transcription factors (MYB TFs) play diverse roles in plant development and stress responses. However, the mechanisms underlying the actions of MYB TFs during stress response remain unclear. In this study we identified a R2R3-MYB TF in soybean (Glycine max), denoted GmMYB84, which contributes to drought resistance. Expression ofGmMYB84was induced by drought, salt stress, H2O2and ABA. Compared Background Expansins are plant cell wall loosening proteins that are involved in cell enlargement and a variety of other developmental processes. The expansin superfamily contains four subfamilies; namely, -expansin (EXPA), -expansin (EXPB), expansin-like A (EXLA), and expansin-like B (EXLB). Although the genome sequencing of soybeans is complete, our knowledge about the pattern of expansion and evolutionary history of soybean expansin genes remains limited.ResultsA total of 75 expansin genes were identified in the soybean genome, and grouped into four subfamilies based on their phylogenetic relationships. Structural analysis revealed that the expansin genes are conserved in each subfamily, but are divergent among subfamilies. Furthermore, in soybean andArabidopsis, the expansin gene family has been mainly expanded through tandem and segmental duplications; however, in rice, segmental duplication appears to be the dominant process that generates this superfamily. The transcriptome atlas revealed notable differential expression in either transcript abundance or expression patterns under normal growth conditions. This finding was consistent with the differential distribution of thecis-elements in the promoter region, and indicated wide functional divergence in this superfamily. Moreover, some critical amino acids that contribute to functional divergence and positive selection were detected. Finally, site model and branch-site model analysis of positive selection indicated that the soybean expansin gene superfamily is under strong positive selection, and that divergent selection constraints might have influenced the evolution of the four subfamilies.ConclusionThis study demonstrated that the soybean expansin gene superfamily has expanded through tandem and segmental duplication. Differential expression indicated wide functional divergence in this superfamily. Furthermore, positive selection analysis revealed that divergent selection constraints might have influenced the evolution of the four subfamilies. In conclusion, the results of this study contribute novel detailed information about the molecular evolution of the expansin gene superfamily in soybean. with the wild type (WT),GmMYB84-overexpressing soybean mutants (OElines) exhibited enhanced drought resistance with a higher survival rate, longer primary root length, greater proline and reactive oxygen species (ROS) contents, higher antioxidant enzyme activities [peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD)], a lower dehydration rate and reduced malondialdehyde (MDA) content. We also found that ROS could induce SOD/POD/CAT activity inOElines. In particular, we found that the optimal level of ROS is required forGmMYB84to modulate primary root elongation. Some ROS-related genes were up-regulated under abiotic stress inGmMYB84transgenic plants compared with the WT. Furthermore, electrophoretic mobility shift assay and luciferase reporter analysis demonstrated that GmMYB84 binds directly to the promoter ofGmRBOHB-1andGmRBOHB-2genes. Based on this evidence, we propose a model for howGmMYB84, H2O2and antioxidant enzymes work together to control root growth under both optimal and drought stress conditions. |
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