Background: High temperature affects a broad spectrum of cellular components and metabolism in plants. The Deg/HtrA family of ATP-independent serine endopeptidases is present in nearly all organisms. Deg proteases are required for the survival of Escherichia coli at high temperatures. However, it is still unclear whether rice Deg proteases are required for chloroplast development under high temperatures.
Results: In this study, we reported the first rice deg mutant tcm5 (thermo-sensitive chlorophyll-deficient mutant 5) that has an albino phenotype, defective chloroplasts and could not survive after the 4-5 leaf seedling stage when grown at high temperature (32 °C). However, when grown at low temperatures (20 °C), tcm5 has a normal phenotype. Map-based cloning showed that TCM5 encoding a chloroplast-targeted Deg protease protein. The TCM5 transcripts were highly expressed in all green tissues and undetectable in other tissues, showing the tissue-specific expression. In tcm5 mutants grown at high temperatures, the transcript levels of certain genes associated with chloroplast development especially PSII-associated genes were severely affected, but recovered to normal levels at low temperatures. These results showed important role of TCM5 for chloroplast development under high temperatures.
Conclusions: The TCM5 encodes chloroplast-targeted Deg protease protein which is important for chloroplast development and the maintenance of PSII function and its disruption would lead to a defective chloroplast and affected expression levels of genes associated with chloroplast development and photosynthesis at early rice seedling stage under high temperatures.
Keywords: Chloroplast development; Deg protease; Photosystem; Rice.