ANALYSIS OF TISSUE-SPECIFIC EXPRESSION OF ARABIDOPSIS-THALIANA HSP9O-FAMILY GENE HSP81

We have isolated three HSP90-family genes from Arabidopsis: HSP81-1 wh ich is heat-inducible, and HSP81-2 and -3 which are highly expressed u nder normal growth temperatures. Northern blot analysis and RNase prot ection analysis, using gene specific probes, showed that HSP81-2 and - 3 mRNA were present in all tissues and abundant in roots, floral bud c lusters, and flowers at 22 degrees C. A small amount of HSP81-1 mRNA w as detected only in roots. In situ hybridization and histochemical ana lysis using transgenic plants carrying chimeric gene fusions, with an HSP81 promotor region fused to a beta-glucuronidase (GUS) gene, confir med these results. At 22 degrees C, high GUS activity was observed in the root apical meristems, pollen and tapeta in HSP81-2::GUS and HSP81 -3::GUS transgenic plants, while only branches of the root in HSP81-1: :GUS transgenic plants expressed high GUS activity. After 2 hours of 3 5 degrees C treatment, extensively high GUS activity was observed in a ll tissues in HSP81-1::GUS transgenic plants, while elevated but tissu e specific expression was observed in HSP81-2 and -3 transgenic plants . Exogenous application of various chemicals such as ABA, GA(3), kinet in, IAA, NaCl, and mannitol revealed that 10 mM IAA and 0.1 M NaCl sig nificantly enhanced the accumulation of HSP81-2 and -3 transcripts. On ly a slight response to IAA was observed in HSP81-1 mRNA accumulation at 22 degrees C; the increase was possibly caused by a novel pathway o ther than heat-shock-response pathway.