Hong‐Feng Zou

WRKY-type transcription factors have multiple roles in the plant defence response and developmental processes. Their roles in the abiotic stress response remain obscure. In this study, 64 GmWRKY genes from soybean were identified, and were found to be differentially expressed under abiotic stresses. Nine GmWRKY proteins were tested for their transcription activation in the yeast assay system, and five showed such ability. In a DNA-binding assay, three proteins (GmWRKY13, GmWRKY27 and GmWRKY54) with a conserved WRKYGQK sequence in their DNA-binding domain could bind to the W-box (TTGAC). However, GmWRKY6 and GmWRKY21, with an altered sequence WRKYGKK, lost the ability to bind to the W-box. The function of three stress-induced genes, GmWRKY13, GmWRKY21 and GmWRKY54, was further investigated using a transgenic approach. GmWRKY21-transgenic Arabidopsis plants were tolerant to cold stress, whereas GmWRKY54 conferred salt and drought tolerance, possibly through the regulation of DREB2A and STZ/Zat10. Transgenic plants over-expressing GmWRKY13 showed increased sensitivity to salt and mannitol stress, but decreased sensitivity to abscisic acid, when compared with wild-type plants. In addition, GmWRKY13-transgenic plants showed an increase in lateral roots. These results indicate that the three GmWRKY genes play differential roles in abiotic stress tolerance, and that GmWRKY13 may function in both lateral root development and the abiotic stress response.

NAC transcription factors play important roles in plant growth, development and stress responses. Previously, we identified multiple NAC genes in soybean (Glycine max). Here, we identify the roles of two genes, GmNAC11 and GmNAC20, in stress responses and other processes. The two genes were differentially induced by multiple abiotic stresses and plant hormones, and their transcripts were abundant in roots and cotyledons. Both genes encoded proteins that localized to the nucleus and bound to the core DNA sequence CGT[G/A]. In the protoplast assay system, GmNAC11 acts as a transcriptional activator, whereas GmNAC20 functions as a mild repressor; however, the C-terminal end of GmANC20 has transcriptional activation activity. Over-expression of GmNAC20 enhances salt and freezing tolerance in transgenic Arabidopsis plants; however, GmNAC11 over-expression only improves salt tolerance. Over-expression of GmNAC20 also promotes lateral root formation. GmNAC20 may regulate stress tolerance through activation of the DREB/CBF-COR pathway, and may control lateral root development by altering auxin signaling-related genes. GmNAC11 probably regulates DREB1A and other stress-related genes. The roles of the two GmNAC genes in stress tolerance were further analyzed in soybean transgenic hairy roots. These results provide a basis for genetic manipulation to improve the agronomic traits of important crops.

The NIMA-related kinases (NEKs) are a family of serine/threonine kinases involved largely in cell cycle control in fungi, mammals and other eukaryotes. In Arabidopsis, NEK6 is involved in the regulation of epidermal cell morphogenesis. However, other roles of NEK6 in plants are less well understood. Here we report functions of NEK6 in plant growth, development and stress responses in Arabidopsis. NEK6 transcripts and proteins are induced by ethylene precursor ACC and salt stress. Expression of other NEK genes except NEK5 is also responsive to the two treatments. Overexpression and mutant analysis disclose that the NEK6 gene increases rosette growth, seed yield and lateral root formation. However, NEK6 appears to play a negative role in the control of seed size. The gene also promotes plant tolerance to salt stress and osmotic stress in its overexpressing plants. The NEK6 gene may achieve its function through suppression of ethylene biosynthesis and activation of CYCB1;1 and CYCA3;1 expression. Our present study reveals new functions of the NEK6 gene in plant growth and stress tolerance, and manipulation of NEK6 may improve important agronomic traits in crop plants.