The Vitis vinifera C-repeat binding protein 4 (VvCBF4) transcriptional factor enhances freezing tolerance in wine grape

Chilling and freezing can reduce significantly vine survival and fruit set in Vitis vinifera wine grape. To overcome such production losses, a recently identified grapevine C‐repeat binding factor (CBF) gene, VvCBF4, was overexpressed in grape vine cv. ‘Freedom’ and found to improve freezing survival and reduced freezing‐induced electrolyte leakage by up to 2 °C in non‐cold‐acclimated vines. In addition, overexpression of this transgene caused a reduced growth phenotype similar to that observed for CBF overexpression in Arabidopsis and other species. Both freezing tolerance and reduced growth phenotypes were manifested in a transgene dose‐dependent manner. To understand the mechanistic basis of VvCBF4 transgene action, one transgenic line (9–12) was genotyped using microarray‐based mRNA expression profiling. Forty‐seven and 12 genes were identified in unstressed transgenic shoots with either a >1.5‐fold increase or decrease in mRNA abundance, respectively. Comparison of mRNA changes with characterized CBF regulons in woody and herbaceous species revealed partial overlaps, suggesting that CBF‐mediated cold acclimation responses are widely conserved. Putative VvCBF4‐regulon targets included genes with functions in cell wall structure, lipid metabolism, epicuticular wax formation and stress‐responses suggesting that the observed cold tolerance and dwarf phenotypes are the result of a complex network of diverse functional determinants.     

ZmABA2, an interacting protein of ZmMPK5, is involved in abscisic acid biosynthesis and functions

In maize (Zea mays), the mitogen‐activated protein kinase ZmMPK5 has been shown to be involved in abscisic acid (ABA)‐induced antioxidant defence and to enhance the tolerance of plants to drought, salt stress and oxidative stress. However, the underlying molecular mechanisms are poorly understood. Here, using ZmMPK5 as bait in yeast two‐hybrid screening, a protein interacting with ZmMPK5 named ZmABA2, which belongs to a member of the short‐chain dehydrogenase/reductase family, was identified. Pull‐down assay and bimolecular fluorescence complementation analysis and co‐immunoprecipitation test confirmed that ZmMPK5 interacts with ZmABA2 in vitro and in vivo. Phosphorylation of Ser173 in ZmABA2 by ZmMPK5 was shown to increase the activity of ZmABA2 and the protein stability. Various abiotic stimuli induced the expression of ZmABA2 in leaves of maize plants. Pharmacological, biochemical and molecular biology and genetic analyses showed that both ZmMPK5 and ZmABA2 coordinately regulate the content of ABA. Overexpression of ZmABA2 in tobacco plants was found to elevate the content of ABA, regulate seed germination and root growth under drought and salt stress and enhance the tolerance of tobacco plants to drought and salt stress. These results suggest that ZmABA2 is a direct target of ZmMPK5 and is involved in ABA biosynthesis and functions.     

Reciprocal regulation between the negative regulator PP2CG1 phosphatase and the positive regulator OST1 kinase confers cold response in Arabidopsis

Protein phosphorylation and dephosphorylation have been reported to play important roles in plant cold responses. In addition, phospho-regulatory feedback is a conserved mechanism for biological processes and stress responses in animals and plants. However, it is less well known that a regulatory feedback loop is formed by the protein kinase and the protein phosphatase in plant responses to cold stress. Here, we report that OPEN STOMATA 1 (OST1) and PROTEIN PHOSPHATASE 2C G GROUP 1 (PP2CG1) reciprocally regulate the activity during the cold stress response. The interaction of PP2CG1 and OST1 is inhibited by cold stress, which results in the release of OST1 at the cytoplasm and nucleus from suppression by PP2CG1. Interestingly, cold-activated OST1 phosphorylates PP2CG1 to suppress its phosphatase activity, thereby amplifying cold signaling in plants. Mutations of PP2CG1 and its homolog PP2CG2 enhance freezing tolerance, whereas overexpression of PP2CG1 decreases freezing tolerance. Moreover, PP2CG1 negatively regulates protein levels of C-REPEAT BINDING FACTORs (CBFs) under cold stress. Our results uncover a phosphor/dephosphor-regulatory feedback loop mediated by PP2CG1 phosphatase and OST1 protein kinase in plant cold responses.