Fine Mapping and Identification of <i>BnaC06.FtsH1</i>, a Lethal Gene That Regulates the PSII Repair Cycle in <i>Brassica napus</i>

• Main Authors: Kai Xu, Yujin Wu, Jurong Song, Kaining Hu, Zengxiang Wu, Jing Wen, Bin Yi, Chaozhi Ma, Jinxiong Shen, Tingdong Fu, Jinxing Tu
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: International Journal of Molecular Sciences
• Subjects: lethal mutant; map-based cloning; FtsH1 hydrolase; PSII repair cycle
• Online Access: https://www.mdpi.com/1422-0067/22/4/2087
• ISSN: 1661-6596; 1422-0067

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 <i>Brassica napus</i>, controlled by double-recessive genes (named<i> cyd1</i> and <i>cyd2</i>). By combining whole-genome resequencing and map-based cloning, <i>CYD1</i> was fine-mapped to a 29 kb genomic region using 15,167 etiolated individuals. Through cosegregation analysis and functional verification of the transgene, <i>BnaC06.FtsH1</i> was determined to be the target gene; it encodes an filamentation temperature sensitive protein H 1 (FtsH1) hydrolase that degrades damaged PSII D1 in <i>Arabidopsis thaliana</i>. The expression of <i>BnaC06.FtsH1</i> was high in the cotyledons, leaves, and flowers of <i>B. napus</i>, and localized in the chloroplasts. In addition, the expression of <i>EngA </i>(upstream regulation gene of FtsH) increased and D1 decreased in 7-521Y. Double mutants of <i>FtsH1</i> and <i>FtsH5 </i>were lethal in <i>A. thaliana</i>. Through phylogenetic analysis, the loss of <i>FtsH5</i> was identified in <i>Brassica</i>, and the remaining <i>FtsH1</i> was required for PSII repair cycle. <i>CYD2</i> may be a homologous gene of <i>FtsH1</i> on chromosome A07 of <i>B. napus</i>. 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.