DELETION ANALYSIS OF THE MAIZE HSP82, HSP81, AND HSP17.9 PROMOTERS INMAIZE AND TRANSGENIC TOBACCO - CONTRIBUTIONS OF INDIVIDUAL HEAT-SHOCKELEMENTS AND RECOGNITION BY DISTINCT PROTEIN FACTORS DURING BOTH HEAT-SHOCK AND DEVELOPMENT

We have previously reported the isolation of the maize heat shock prot ein (HSP) genes hsp82, hsp81 and hsp17.9, which are highly expressed i n maize plants during heat stress as well as during the normal course of development of embryos and pollen in the absence of heat (MARRS et al., 1993; DIETRICH et al., 1992). Here we determine the contributions of individual HSEs to the overall heat-induciblity of each promoter b y utilizing beta-glucuronidase (GUS) reporter gene expression driven b y promoter deletion constructs in maize protoplasts. Heat-inducible ex pression is highest from full-length promoters containing several HSEs , yet constructs retaining only a single HSE can confer up to 90% of t he heat-inducibility to the promoters. By generation of transgenic tob acco plants stably transformed with the various maize HSP promoter-GUS reporter gene constructs, we show that the overall patterns of develo pmental regulation and heat-inducibility seen previously in maize tiss ues are conserved in tobacco. Results from gel mobility shift analysis indicate that nuclear binding factors present in extracts from heat s hocked maize tissues have the highest affinity for the TATA-proximal H SE of both the hsp81 and hsp82 promoters, with decreasing affinity cor related with increasing distance from the TATA box. We also show that HSE-specific protein/DNA complexes form when proteins from developing embryos or tassels are used in the binding assays. The complexes forme d using HSEs with nuclear proteins from heat-shocked leaves or develop ing embryos and tassels differ in mobility, indicating that the HSE ma y serve as a shared binding site for different types of protein comple xes during both heat shock and development.