Tomato Heat Shock Protein 21

The Plant Cell, Vol. 17, 1829–1838, June 2005, www.plantcell.org ª 2005 American Society of Plant Biologists

Dual Role for Tomato Heat Shock Protein 21: Protecting
Photosystem II from Oxidative Stress and Promoting
Color Changes during Fruit Maturation
Inbal Neta-Sharir,a Tal Isaacson,b Susan Lurie,c and David Weissa,1 a Robert

H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food, and Environmental
Quality Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel b Department of Genetics, Hebrew University of Jerusalem, Jerusalem 91904, Israel c Department of Postharvest Science, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel

The tomato (Lycopersicon esculentum) chloroplast small heat shock protein (sHSP), HSP21, is induced by heat treatment in leaves, but also under normal growth conditions in developing fruits during the transition of chloroplasts to chromoplasts.
We used transgenic tomato plants constitutively expressing HSP21 to study the role of the protein under stress conditions and during fruit maturation. Although we did not find any effect for the transgene on photosystem II (PSII) thermotolerance, our results show that the protein protects PSII from temperature-dependent oxidative stress. In addition, we found direct evidence of the protein’s role in fruit reddening and the conversion of chloroplasts to chromoplasts. When plants were grown under normal growth temperature, transgenic fruits accumulated carotenoids earlier than controls. Furthermore, when detached mature green fruits were stored for 2 weeks at 28C and then transferred to room temperature, the natural accumulation of carotenoids was blocked. In a previous study, we showed that preheat treatment, which induces HSP21, allowed fruit color change at room temperature, after a cold treatment. Here, we show that mature green transgenic fruits constitutively expressing HSP21 do not require the heat treatment to

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