AUTHOR=Zhong Xionghui , Yue Xiangqing , Cui Jian , Han Rui , Gao Yi , Kang Jungen 

TITLE=Complete mitochondrial genome sequencing and identification of candidate genes responsible for C5-type cytoplasmic male sterility in cabbage (B. oleracea var. capitata)

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.1019513

DOI=10.3389/fpls.2022.1019513

ISSN=1664-462X

ABSTRACT=<p>Cytoplasmic male sterility (CMS) is widely used in cruciferous vegetables hybrid breeding. The C5-type CMS cabbage line exhibits stable male sterility and offers great value for cabbage breeding. However, the underlying CMS mechanism remains unclear. Here, the complete mitochondrial genome was sequenced and assembled for this line. The genome size was 221,862 bp. Mitochondrial genome comparison showed that the mitochondrial genome was likely generated by recombination with a <italic>nap</italic>-type CMS <italic>B. napus</italic> strain. Sixty-seven unknown-function open reading frames (ORFs) were identified. Seven <italic>orfs</italic>, <italic>orf114a</italic>, <italic>orf123a</italic>, <italic>orf188a</italic>, <italic>orf</italic>222a, <italic>orf</italic>261a, <italic>orf286a</italic>, and <italic>orf322a</italic>, were specifically identified in this genome. The presence of these candidate CMS genes decreased ATPase activity and ATP content by affecting the transcript levels of energy metabolism-related genes and F<sub>1</sub>F<sub>0</sub>-ATP synthase assembly. Among them, <italic>orf188a</italic>, <italic>orf222a</italic>, <italic>orf261a</italic>, <italic>orf286a</italic>, and <italic>orf322a</italic> possessed a transmembrane structure, and <italic>orf188a</italic> was cotranscribed with <italic>rps7</italic> and <italic>trnfM</italic>. <italic>orf222a</italic> was partially homologous to <italic>atp8</italic> and coexpressed with <italic>nad5</italic>. <italic>orf261a</italic> and <italic>orf322a</italic> were cotranscribed with <italic>cox1</italic> and <italic>atp9</italic>, respectively. Additionally, <italic>orf114a</italic> was cotranscribed with <italic>atp8</italic>. Yeast two-hybrid assays showed that the ORF222a protein interacts with a <italic>B. oleracea</italic> ATP17 homolog (<italic>Bo7g114140</italic>) during F<sub>0</sub>-type ATP synthase assembly, reducing the quantity and activity of assembled F<sub>1</sub>F<sub>0</sub>-ATP synthase. Cytological sections showed that premature separation of the tapetum from the connective tissue and delayed tapetal programmed cell death (PCD) might be the immediate causes of CMS in C5-type CMS cabbage lines. Our results may help uncover the molecular mechanism of C5-type CMS in <italic>B. oleracea</italic> from the perspectives of the whole mitochondrial genome and cytology of anther development.</p>