The two mutants were albino lethal at high temperatures and showed decreased chlorophyll accumulation, abnormal chloroplast ultrastructure, and attenuated photosynthetic activity. 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. RNA sequencing data suggests 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 not only regulates transcription of the PEP-encoded genes but also maintains the redox balance in chloroplasts under heat stress. Furthermore, the wlp2w mutant gene represents a potential advantage in enhancing seed purity and high-throughput breeding.
These results strongly indicate that WLP2 protects chloroplast development from heat stress via a TRX-FLN regulatory module in rice.
(A–C) Expression levels of PEP-dependent genes (A), NEP-dependent genes (B) and photosynthesis-associated genes (C) in 3-week-old seedlings of wild-type (WT), wlp2s, and wlp2w grown at 28 °C. (D) Heat map of gene expression in plants grown at 22 °C and 32 °C; the gene expression of WT plants represents a relative standard (Log2(RPKM)=0) at 32 °C. Data are shown as means±SD from three individual replicates.