CHARACTERIZATION OF 2 MAIZE HSP90 HEAT-SHOCK PROTEIN GENES - EXPRESSION DURING HEAT-SHOCK, EMBRYOGENESIS, AND POLLEN DEVELOPMENT

We have isolated two genes from Zea mays encoding proteins of 82 and 8 1 kD that are highly homologous to the Drosophila 83-kD heat shock pro tein gene and have analyzed the structure and pattern of expression of these two genes during heat shock and development. Southern blot anal ysis and hybrid select translations indicate that the highly homologou s hsp82 and hsp81 genes are members of a small multigene family compos ed of at least two and perhaps three or more gene family members. The deduced amino acid sequence of these proteins based on the nucleotide sequence of the coding regions shows 64-88% amino acid homology to oth er hsp90 family genes from human, yeast, Drosophila, and Arobidopsis. The promoter regions of both the hsp82 and hsp81 genes contain several heat shock elements (HSEs), which are putative binding sites for heat shock transcription factor (HSF) commonly found in the promoters of o ther heat shock genes. Gene-specific oligonucleotide probes were synth esized and used to examine the mRNA expression patterns of the hsp81 a nd hsp82 genes during heat shock, embryogenesis, and pollen developmen t. The hsp81 gene is only mildly heat inducible in leaf tissue, but is strongly expressed in the absence of heat shock during the pre-meioti c and meiotic prophase stages of pollen development and in embryos, as well as in heat-shocked embryos and tassels. The hsp82 gene shows str ong heat inducibility at heat-shock temperatures (37-42-degrees-C) and in heat shocked embryos and tassels but is only weakly expressed in t he absence of heat shock. Promoter-GUS reporter gene fusions made and analyzed by transient expression assays in Black Mexican Sweet (BMS) M aize protoplasts also indicate that the hsp82 and hsp81 are regulated differentially. The hsp82 promoter confers strong heat-inducible expre ssion of the GUS reporter gene in heat-treated cells (60- to 80-fold o ver control levels), whereas the hsp81 promoter is only weakly heat in ducible (5- to 10-fold over control levels).