Abstract
BackgroundHigh 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.ResultsIn 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-016-0086-5) contains supplementary material, which is available to authorized users.
Highlights
High temperature affects a broad spectrum of cellular components and metabolism in plants
photosystem II (PSII) activity of the 3-leaf-stage tcm5 and wild type (WT) seedlings at 20 and 32 °C was surveyed by measuring the ratio of variable fluorescence to maximum fluorescence as follows: Fv/Fm = (Fm-Fo)/Fm, where Fo and Fm are minimum and maximum chlorophyll a fluorescence of dark-adapted leaves, respectively
At 32 °C, the ΦPSII value was 0.624 ± 0.04 in WT plants and 0.361 ± 0.04 in tcm5 mutants, showing that the photosynthesis efficiency was significantly reduced in tcm5 mutants
Summary
High temperature affects a broad spectrum of cellular components and metabolism in plants. Deg proteases are required for the survival of Escherichia coli at high temperatures. It is still unclear whether rice Deg proteases are required for chloroplast development under high temperatures. The family of Deg proteases (for degradation of periplasmic proteins) (Strauch and Beckwith 1988), named as HtrA proteases (for high temperature requirement A) (Lipinska et al 1988), is one important group among proteolytic enzymes. A first E.coli DegP was identified based on the fact that it is required for the survival at high temperatures (Lipinska et al 1988, 1990; Strauch and Beckwith 1988). The Deg proteases were reported to chloroplast-located be involved in the degradation of damaged photosynthetic proteins, especially the photosystem II (PSII) reaction center D1 protein (Kato et al 2012). To our knowledge, any deg rice mutants have not been reported yet, still less the function
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