Characteristic And Functional Analysis Of Heat Shock Transcriptional Factor Carhsfb2 In Chickpea (Cicer Arietinum L.)

Abiotic stress, such as drought, salinity, high and low temperatures, always affects crop growth and grain yield. Plant cells under some kinds of adversity stress, experience stress signals by the changes of free radicals and osmotic pressure, and enhance the expression levels of some hormones, such as ABA. The transcription factors are induced during signal transmission process caused by hormones and second messenger. Transcription factors identify and specifically bind cis-acting elements. The stress tolerance of plants was enhanced by the expression of related genes. The same transcription factor or gene expression can be detected under different stress conditions, such cross-adaptation phenomenon are common in plants.Our research group established a drought related cDNA library with chickpea and found that CarHSFB2 gene is related to drought stress. Many higher eukaryotes only have less three heat shock factors (HSFs), but plants have more than 20 HSFs, designated class A, B, and C. However, those transcription factors have a feature of diversity and redundancy in their function. Studies have shown that heat shock transcription factors play a role in three ways, most of class A transcription factors have transcriptional activation, class B may play a role of assist or inhibition function. When it comes to class C, few reports is known.In my study, the validity of CarHSFB2 gene was determined by compared with chickpea genome sequence information published on the NCBI website. The ORF length of CarHSFB2 was slightly shorter than the other members of the class B family of transcription factors. CarHSFB2 gene has a N-terminal conservative DNA binding domain, and contains an intron with 87bp. Based on phylogenetic analysis, this gene has a close evolutionary relationship with AtHSFB2a gene. CarHSFB2 was intracellular protein and contain potential phosphorylation sites. The CarHSFB2 was cloned into the yeast expression vector pDBLeu and transformed yeast Mav203. However, we found that CarHSFB2 did not have transcription activation. Moreover, we did not find a domain with high transcriptional activity as well.We conducted a functional verification with T3 generation transgenic Arabidopsis overexpressing CarHSFB2 gene. We found that CarHSFB2 gene was related to drought and basis heat resistance of Arabidopsis. With 3 hours’ drought stress, transcription accumulation of RD29A gene in transgenic Arabidopsis was higher than the wild type. Also, after 150mM D-mannitol drought stress, transgenic Arabidopsis relative conductivity was lower than the wild-type Arabidopsis. Under high temperature stress, the differences about transgenic Arabidopsis with wild type were showed as following:1) Under the conditions of 46℃ with 1 hour treatment, transcript accumulation of AtHSFA2 is still higher than the wild type; 2) After the heat treatment during germination, germination rate is lower than the wild type; 3) Transgenic Arabidopsis of 3 days seedlings has a higher survival rate at 46℃ with 70min treatment. The survival rate of Wild-type Arabidopsis has greatly improved after a mild heat treatment. These thermal characteristics were similar to 35S:AtHSFA3 plants. These findings reveal CarHSFB2 gene may act as a co-activator, and be involved in drought and high temperature stress.In addition, transgenic Arabidopsis have no significant differences on the phenotypic characteristics, except a later flowering period. Transgenic Arabidopsis also have a higher tolerance to salt stress. But CarHSFB2 cannot improve cold tolerance of transgenic Arabidopsis. This study shows that the class B heat shock transcription factor may have different functions in different crops. Next, the regulatory mechanisms of CarHSFB2 gene would be further explored through gene interactions or transcriptome level.