Acquired thermotolerance and expression of the HSP100/ClpB genes of lima bean

Acquired thermotolerance (AT) is the ability of cells to survive a normally lethal temperature treatment as a consequence of pretreatment at an elevat ed but sublethal temperature. In yeast and cyanobacteria, the expression of the HSP100/ClpB protein is required for the AT response. To determine whet her the HSP100/ClpB protein is associated with this response in lima bean ( Phaseolus Iunatus), we have cloned an HSP100/ClpB homolog and assessed expr ession of the two gene copies under heat stress conditions, which induce AT . Transcription of the cytoplasmically localized HSP100/ClpB protein genes is stringently controlled by heat stress in both of the laboratory and fiel d heat stress conditions. From a heat-induced cDNA library, we identified a clone of a putative chloroplast targeted (cp) HSP100/ClpB protein gene seq uence. The cp HSP100/ClpB protein genes are constitutively expressed, but t ranscript levels increase post-heat stress in laboratory heat stress experi ments. In field conditions the genes for the cp HSP100/ClpB are constitutiv ely expressed. Although we were unable to correlate differences in the timi ng of AT response with the expression or genetic structure of the HSP100/Cl pB genes in heat-tolerant or -sensitive varieties of lima bean, we clearly demonstrate the association of expression of HSr100/ClpB proteins with heat response in this species.