Soybean [Glycine max (L.) Merri.] is an important oilseed and food crop. In recent years, environmental degradation has accelerated soil alkalization, salinization, and water deficit, which have seriously threatened the soybean quality and yield. Chaperone DNAJ proteins play important roles in plant response to a number of abiotic and biotic stresses. Here, we investigated the function of a soybean DNAJ gene, GmDNAJC7, in plant tolerance to abiotic stresses. GmDNAJC7 gene expression was induced by alkaline-salt, salt, and drought treatments in soybean roots, suggesting its possible role in soybean response to these stresses. GmDNAJC7 overexpression improved the alkaline-salt tolerance of soybean composite plants, which showed a higher SPAD (Soil and Plant Analysis Development) value for chlorophyll content and leaf relative water content than the control plants after NaHCO3 treatment. Moreover, the GmDNAJC7 overexpressing Arabidopsis had a higher germination rate and average root length than the wild type and dnajc7 mutant, under NaHCO3, NaCl, and mannitol stresses, indicating that the ectopic expression of the GmDNAJC7 gene enhanced the alkaline-salt, salt, and drought tolerance in Arabidopsis. These findings suggest that GmDNAJC7 is involved in the alkaline-salt, salt, and drought tolerance in Arabidopsis and soybean. This study provides new insights into the role of DNAJ proteins in plant tolerance to abiotic stress.
The SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL) transcription factor play vital roles in plant growth and development. Although 15 SPL family genes have been recognized in the model medical plant Salvia miltiorrhiza Bunge, most of them have not been functionally characterized to date. Here, we performed a careful characterization of SmSPL2, which was expressed in almost all tissues of S. miltiorrhiza and had the highest transcriptional level in the calyx. Meanwhile, SmSPL2 has strong transcriptional activation activity and resides in the nucleus. We obtained overexpression lines of SmSPL2 and rSmSPL2 (miR156-resistant SmSPL2). Morphological changes in roots, including longer length, fewer adventitious roots, decreased lateral root density, and increased fresh weight, were observed in all of these transgenic lines. Two rSmSPL2-overexpressed lines were subjected to transcriptome analysis. Overexpression of rSmSPL2 changed root architectures by inhibiting biosynthesis and signal transduction of auxin, while triggering that of cytokinin. The salvianolic acid B (SalB) concentration was significantly decreased in rSmSPL2-overexpressed lines. Further analysis revealed that SmSPL2 binds directly to the promoters of Sm4CL9, SmTAT1, and SmPAL1 and inhibits their expression. In conclusion, SmSPL2 is a potential gene that efficiently manipulate both root architecture and SalB concentration in S. miltiorrhiza.
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