Identification of a novel bZIP transcription factor in Camellia sinensis as a negative regulator of freezing tolerance in transgenic arabidopsis.

Abstract

Basic region/leucine zipper (bZIP) transcription factors play vital roles in the abiotic stress response of plants. However, little is known about the function of bZIP genes in Camellia sinensis . CsbZIP6 was overexpressed in Arabidopsis thaliana . Effects of CsbZIP6 overexpression on abscisic acid (ABA) sensitivity, freezing tolerance and the expression of cold-responsive genes in arabidopsis were studied. CsbZIP6 was induced during cold acclimation in tea plant. Constitutive overexpression of CsbZIP6 in arabidopsis lowered the plants' tolerance to freezing stress and ABA exposure during seedling growth. Compared with wild-type (WT) plants, CsbZIP6 overexpression (OE) lines exhibited increased levels of electrolyte leakage (EL) and malondialdehyde (MDA) contents, and reduced levels of total soluble sugars (TSS) under cold stress conditions. Microarray analysis of transgenic arabidopsis revealed that many differentially expressed genes (DEGs) between OE lines and WT plants could be mapped to 'response to cold' and 'response to water deprivation' terms based on Gene Ontology analysis. Interestingly, CsbZIP6 overexpression repressed most of the cold- and drought-responsive genes as well as starch metabolism under cold stress conditions. The data suggest that CsbZIP6 functions as a negative regulator of the cold stress response in A. thaliana , potentially by down-regulating cold-responsive genes.