Characterization of Arabidopsis heat shock protein 70 (HSP70) gene family and microarray analysis of gene expression in response to temperature extremes

Twelve full-length and two truncated DnaK type heat shock protein 70 (hsp70) genes have been identified in Arabidopsis since the completion of the genome sequencing project. While the biochemical mechanism and structure of hsp70 are highly conserved among organisms, the physiological roles of hsp70s in plants remain largely unknown due to promiscuous substrate specificity and functional redundancy of individual hsp70s. To characterize the roles of hsp70 genes in Arabidopsis, the following objectives were undertaken: (1) a comprehensive RT-PCR and genomic analysis for the hsp70 gene family, (2) transgenic approach to over/underexpress two members of the hsp70 gene family, cytosolic Hsc70-1 and ER luminal BiP-2, and (3) microarray analysis of gene expression during induction of acquired thermotolerance. I isolated two nuclear-encoded, organellar members of the Arabidopsis hsp70 gene family mtHsc70-2 (AF217458) and cpHsc70-2 (AF217459). Genomic analysis revealed several unique characteristics of the subfamily of Arabidopsis hsp70 gene family such as gene structure, sequence relatedness, C-terminal sequence motifs. RT-PCR analysis established the complex differential expression pattern for the hsp70s in Arabidopsis that suggests specialized functions even among members localized to the same subcellular compartment. Transgenic analysis showed that the tight regulation of cytosolic Hsc70-1 expression is essential to viability of plants and that increased BiP-2 protein levels enhanced the survival of seed after heat stress. Microarray analysis identified genes that are commonly induced or repressed in response to temperature extremes. The expression patterns of the genes in the microarray also suggested that the membrane components and the photosynthetic apparatus are primary targets for temperature stresses.