PE-1, Encoding Heme Oxygenase 1, Impacts Heading Date and Chloroplast Development in Rice ( Oryza sativa L.)

The duration of the rice growth phase has always been an important target trait. The identification of mutations in rice that alter these processes and result in a shorter growth phase could have potential benefits for crop production. In this study, we isolated an early aging rice mutant, pe-1, with light green leaves, using γ-mutated indica rice cultivar and subsequent screening methods, which is known as the phytochrome synthesis factor Se5 that controls rice flowering. The pe-1 plant is accompanied by a decreased chlorophyll content, an enhanced photosynthesis, and a decreased pollen fertility. PE-1, a close homologue of HY1, is localized in the chloroplast. Expression pattern analysis indicated that PE-1 was mainly expressed in roots, stems, leaves, leaf sheaths, and young panicles. The knockout of PE-1 using the CRISPR/Cas9 system decreased the chlorophyll content and downregulated the expression of PE-1-related genes. Furthermore, the chloroplasts of pe-1 were filled with many large-sized starch grains, and the number of osmiophilic granules (a chloroplast lipid reservoir) was significantly decreased. Altogether, our findings suggest that PE-1 functions as a master regulator to mediate in chlorophyll biosynthesis and photosynthetic pathways.