Generation of transgenic rice expressing heat shock protein genes under cool conditions

抄録

The heat shock response of rice, including expression of heat shock transcription factors (Hsfs), was investigated to elucidate the molecular regulation of its high-temperature tolerance. In silico analysis revealed that the rice genome encodes more than 19 species of Hsf genes that can be organized into three classes, A, B, and C. Rice seedlings treated with high temperature, express three class A Hsf genes (HsfA2a, HsfA2c, and HsfA2d) and two class B Hsf genes (HsfB2b and HsfB2c) at significantly elevated levels. Transgenic rice plants overexpressing these three class A Hsf genes controlled by the rice actin 1 promoter or the wheat cold response (WCR) promoter expressed the transgenes, but did not express heat shock response genes such as small HSPs, whose expression is controlled by Hsfs. Treatment with geldanamycin, an inhibitor of HSP90, elevated the expression of HSPs in the WCR::Hsf transformant. Therefore, transgenic rice co-expressing WCR::Hsfs and a dominant negative HSP90 mutant were generated in which the heat shock response could be induced under WCR promoter-activating conditions. Successful induction of the heat shock response under cool conditions in this co-expression line suggests that HSP90 controls the heat shock response via the activity of Hsf in rice cells.