Identification of Thermo-Sensitive Chloroplast Development Gene TSCD5 Required for Rice Chloroplast Development under High Temperature

Chloroplasts are critical organelles for photosynthesis and play significant roles in plant growth and metabolism. High temperature is one of abiotic stresses affecting the growth and development of plants, involving chlorophyll biosynthesis and chloroplast development. It is well known that the methyl erythritol 4-phosphate (MEP) pathway is vital to photosynthesis and plant growth, and 1-deoxy-D-xylulose-5-phosphate synthase (DXS) is the enzyme that catalyze the first step of the MEP pathway. Although DXS has been widely studied in microbes and plants, no DXS gene has been identified in rice. Here, a novel thermo-sensitive chlorophyll-deficient 5 (tscd5) mutant was isolated in rice with decreased chlorophyll contents, impaired chloroplasts, and albino leaves at high temperature (35 °C). Fine mapping and DNA sequencing of TSCD5 found a missense mutation (G to A) in the sixth exon of LOC_Os05g33840 in tscd5 . The TSCD5 gene encodes a 1-deoxy-D-xylulose-5-phosphate synthase 1 ( OsDXS1 ) localized in chloroplast. Complementation tests and overexpression assay demonstrated that the mutation in LOC_Os05g33840 caused the tscd5 phenotype. qRT-PCR of TSCD5 showed it was constitutively expressed in all tissues, and its transcript amounts were reduced in tscd5 under high temperature. Here, TSCD5 is verified to be crucial to chloroplast development under high temperature in rice, which may facilitate the elucidation of the molecular mechanisms which underlie acclimation to high temperature stress in plants.