Fine Mapping and Identification of , a Lethal Gene That Regulates the PSII Repair Cycle in .

Photosystem II (PSII) is an important component of the chloroplast. The PSII repair cycle is crucial for the relief of photoinhibition and may be advantageous when improving stress resistance and photosynthetic efficiency. Lethal genes are widely used in the efficiency detection and method improvement of gene editing. In the present study, we identified the naturally occurring lethal mutant 7-521Y with etiolated cotyledons in , controlled by double-recessive genes (named and ). By combining whole-genome resequencing and map-based cloning, was fine-mapped to a 29 kb genomic region using 15,167 etiolated individuals. Through cosegregation analysis and functional verification of the transgene, was determined to be the target gene; it encodes an filamentation temperature sensitive protein H 1 (FtsH1) hydrolase that degrades damaged PSII D1 in . The expression of was high in the cotyledons, leaves, and flowers of , and localized in the chloroplasts. In addition, the expression of (upstream regulation gene of FtsH) increased and D1 decreased in 7-521Y. Double mutants of and were lethal in . Through phylogenetic analysis, the loss of was identified in , and the remaining was required for PSII repair cycle. may be a homologous gene of on chromosome A07 of . Our study provides new insights into lethal mutants, the findings may help improve the efficiency of the PSII repair cycle and biomass accumulation in oilseed rape.