Brassica evolution of essential BnaFtsH1 genes involved in the PSII repair cycle and loss of FtsH5.

The PSII repair cycle is an important part of photosynthesis and is essential for high photosynthetic efficiency. The study of essential genes in Brassica napus provides significant potential for the improvement of gene editing technology and molecular breeding design. Previously, we identified a B. napus lethal mutant (7-521Y), which was controlled by two recessive genes (cyd1 and cyd2). BnaC06.FtsH1 was identified as a CYD1 target gene through functional verification. In the present study, we employed fine-mapping, genetic complementation, and CRISPR/Cas9 experiments to identify BnaA07.FtsH1 as the target gene of CYD2, functioning similarly to BnaC06.FtsH1. By analyzing CRISPR/Cas9 T generation plants of the Westar variety, we found that the copy number of FtsH1 was positively correlated with its biomass accumulation. Transcriptome analysis of cotyledons revealed differences in the expression of photosynthesis antenna and structural proteins between the mutant and complementary seedlings. Phylogenetic and chromosome linear analyses, based on 15 sequenced cruciferous species, revealed that Brassica alone had lost FtsH5 during evolution. This may be related to the fact that FtsH5 was located at the end of chromosome ABK8 in the ancestor species. Cloning and identification of BnaFtsH1s provide a deeper understanding of PSII repair cycle mechanisms and offer new insights for the improvement of photosynthetic efficiency and molecular breeding design in B. napus.