Modified expression of a carrot small heat shock protein gene, Hsp17.7, results in increased or decreased thermotolerance

We have determined that one small heat shock protein gene, encoding Hsp17.7 , plays an important role in the ability of carrot cells and plants to surv ive thermal stress. Transgenic cells and regenerated plants were generated in which the carrot Hsp17.7 gene was either constitutively expressed (denot ed CaS lines) or expressed as a heat inducible antisense RNA (denoted AH li nes). Thermotolerance measurements demonstrated that CaS lines were more th ermotolerant than vector controls and AH antisense lines were less thermoto lerant than vector controls. RNA analysis demonstrated that Hsp17.7 mRNA wa s detectable, but not abundant, prior to heat shock in CaS cells, but not i n vector control cells. Conversely, RNA analysis of antisense cells showed that, after heat shock, the amounts of mRNA for Hsp17.7 was moderately less abundant in AH cells than in vector controls. Analysis of protein synthesi s in CaS cells did not indicate substantial synthesis or accumulation of Hs p17.7, or any small Hsp, at 23 degrees C. However, in the most thermotolera nt line, protein synthesis was maintained at a higher rate than in other ce ll lines at a more extreme heat shock (42 degrees C). In contrast, antisens e AH cells showed reduced synthesis of many Hsp, large and small. These res ults suggest that the Hsp17.7 gene plays a critical, although as yet not un derstood, role in thermotolerance in carrot. This represents the first demo nstration of the ability to both increase and decrease thermotolerance by t he manipulation of expression of a single gene.