Membrane-anchored receptor-like protein kinases (RLKs) recognize extracellular signals at the cell surface and activate the downstream signaling pathway by phosphorylating specific target proteins. We analyzed a receptor-like cytosolic kinase (RLCK), ARCK1, whose expression was induced by abiotic stress. ARCK1 belongs to the cysteine-rich repeat (CRR)-RLK subfamily and encodes a cytosolic protein kinase. The arck1 mutant showed higher sensitivity than the wild-type to ABA and osmotic stress during the postgerminative growth phase. CRK36, an abiotic stress-inducible RLK belonging to the CRR-RLK subfamily, was screened as an interacting factor with ARCK1 by co-expression analyses and a yeast two-hybrid system. CRK36 physically interacted with ARCK1 in plant cells and the kinase domain of CRK36 phosphorylated ARCK1 in vitro. We generated CRK36 RNAi transgenic plants and the transgenic plants with suppressed CRK36 expression showed higher sensitivity than arck1-2 to ABA and osmotic stress during the postgerminative growth phase. Microarray analysis using CRK36 RNAi plants revealed that the suppression of CRK36 up-regulates several ABA-responsive genes, such as LEAs, oleosin, ABI4, and ABI5. These results suggest that CRK36 and ARCK1 form a complex and negatively control ABA and osmotic stress signal transduction.
The BRASSINOSTEROID INSENSITIVE1 (BRI1) receptor kinase has recently been shown to possess tyrosine kinase activity, and preventing autophosphorylation of the tyrosine-831 regulatory site by site-directed mutagenesis enhances shoot growth. In this study, we characterized the increased leaf growth of Arabidopsis (Arabidopsis thaliana) plants expressing BRI1(Y831F)-Flag compared with BRI1-Flag (both driven by the native promoter and expressed in the bri1-5 weak allele background) and provide insights into the possible mechanisms involved. On average, relative leaf growth rate was increased 16% in the Y831F plants (in the bri1-5 background), and the gain of function of the Y831F-directed mutant was dominant in the wild-type background. Leaves were larger as a result of increased cell numbers and had substantially increased vascularization. Transcriptome analysis indicated that genes associated with brassinolide biosynthesis, secondary cell wall biosynthesis and vascular development, and regulation of growth were altered in expression and may contribute to the observed changes in leaf architecture and whole plant growth. Analysis of gas exchange and chlorophyll fluorescence indicated that Y831F mutant plants had higher rates of photosynthesis, and metabolite analysis documented enhanced accumulation of starch, sucrose, and several amino acids, most prominently glycine and proline. These results demonstrate that mutation of BRI1 can enhance photosynthesis and leaf growth/vascularization and may suggest new approaches to increase whole plant carbon assimilation and growth.
Stress responses in plants are tightly coordinated with developmental processes, but interaction of these pathways is poorly understood. We used genome-wide assays at high spatiotemporal resolution to understand the processes that link development and stress in the Arabidopsis root. Our meta-analysis finds little evidence for a universal stress response. However, common stress responses appear to exist with many showing cell type specificity. Common stress responses may be mediated by cell identity regulators because mutations in these genes resulted in altered responses to stress. Evidence for a direct role for cell identity regulators came from genome-wide binding profiling of the key regulator SCARECROW, which showed binding to regulatory regions of stress-responsive genes. Coexpression in response to stress was used to identify genes involved in specific developmental processes. These results reveal surprising linkages between stress and development at cellular resolution, and show the power of multiple genome-wide data sets to elucidate biological processes.