Temperature-mediated shifts in chlorophyll biosynthesis in leaves of chlorophyll b-lacking rice (Oryza sativa L.)

Extreme temperatures have become a threat to crop yields. To maintain plant growth and yield, chlorophyll (Chl) biosynthesis plays a crucial role in adaptation to temperature stress. This study investigated the influence of temperature on the biosynthesis and characteristics of pigments (Chl a, Chl b, and carotenoids) in the leaves of Chl b-lacking mutant rice (Chlorina 1, ch1) and wild-type rice (Norin No.8, wt). The ch1 showed thinner stacked grana caused by a decrease in thylakoid membranes per granum at 15 °C, whereas the destacked grana were observed at 35 °C after 12 h incubation. However, the grana are stacked normally, along with the absence of Chl b, and a significantly decreased amount of Chl a in both wt and ch1 were observed after heat stress exposure, demonstrating that light-harvesting complex II proteins are involved in grana stacking. Ch1 was sensitive to 15 °C during the first 4 h of incubation but it subsequently adapted to the cold environment. In addition, there were no significant differences in the photosynthesis between wt and ch1 after 12 h incubation at 35 °C. Differentially expressed gene (DEGs) analysis revealed that GluRS expression decreased, which resulted in a decline in Chl biosynthesis in wt and ch1 at 35 °C. At 8 h and 12 h, there were no significant differences in the expression of DEGs involved in Chl biosynthesis and degradation between wt and ch1 at 15 °C. ALAD expression in wt and ch1 at 15 °C decreased until it was undetectable. These findings suggested that ch1 may adapt to temperatures ranging from 15 °C to 35 °C.