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White Leaf and Panicle 2, Encoding a PEP-associated Protein, is Required for Chloroplast Biogenesis under Heat Stress in Rice

Source: China National Rice Research Institute

Recently, an important progress on new regulatory mechanism of chloroplast biogenesis under higher temperature stress was achieved by a research team led by Professor Hu Peisong from China National Rice Research Institute of Chinese Academy of Agricultural Sciences (CAAS).

The plastid-encoded RNA polymerase (PEP) plays an important role in the transcription machinery of mature chloroplasts, which is coated by additional proteins such as PEP-associated protein (PAPs) to build a larger chloroplast-specific PEP complex. Previous investigations in Arabidopsis suggested that PAPs displayed potential functions in DNA/RNA metabolism, PEP complex protection and redox regulation; PAPs also affect the activity and integrity of the PEP complex to further regulate the chloroplast transcriptional machinery. However, details of its function remain elusive in rice.

In this study, a novel PAP (WLP2) in rice was identified by a map-based cloning strategy. Two mutants wlp2w and wlp2s were albino lethal at high temperatures. Map-based cloning suggested that WLP2 encodes a putative pfkB-type carbohydrate kinase family protein, which is homologous to fructokinase-like 1 (AtFLN1) in Arabidopsis. WLP2 is mainly expressed in green tissues and its protein localizes in chloroplasts. Expression levels of PEP-encoded genes, chloroplast development genes and photosynthesis-related genes were compromised in wlp2 mutants, indicating that WLP2 is essential for normal chloroplast biogenesis. Moreover, WLP2 and its paralog OsFLN2 can physically interact with thioredoxin OsTRXz to form a TRX-FLN regulatory module, which regulates transcription of the PEP-encoded genes and maintains the redox balance in chloroplasts under heat stress. Furthermore, the wlp2w mutant gene has a potential advantage in enhancing seed purity and high-throughput breeding. The results strongly indicate that WLP2 protects chloroplast development from heat stress via a TRX-FLN regulatory module in rice.

PhD. student Lv Yusong and Dr. Shao Gaoneng are co-first authors of this study, which is supported by the National Key Research and Development Program of China (Grant No.: 2016YFD0101801), the National Natural Science Foundation of China (Grant No.: 31501285, 31521064), the Science Foundation of Zhejiang province (Grant No.: LY14C130009) and the National S&T Major Project (Grant No.: 2016ZX08001006). The study findings have been published online in Journal of Experimental Botany (DOI: 10.1093/jxb/erx332). More details can be accessed on the link below:

By Wei Xiangjin