Organelle Comparative Genome Analysis Reveals Novel Alloplasmic Male Sterility with orf112 in Brassica oleracea L.

Abstract

B. oleracea Ogura CMS is an alloplasmic male-sterile line introduced from radish by interspecific hybridization and protoplast fusion. The introduction of alien cytoplasm resulted in many undesirable traits, which affected the yield of hybrids. Therefore, it is necessary to identify the composition and reduce the content of alien cytoplasm in B. oleracea Ogura CMS. In the present study, we sequenced, assembled, and compared the organelle genomes of Ogura CMS cabbage and its maintainer line. The chloroplast genome of Ogura-type cabbage was completely derived from normal-type cabbage, whereas the mitochondrial genome was recombined from normal-type cabbage and Ogura-type radish. Nine unique regions derived from radish were identified in the mitochondrial genome of Ogura-type cabbage, and the total length of these nine regions was 35,618 bp, accounting for 13.84% of the mitochondrial genome. Using 32 alloplasmic markers designed according to the sequences of these nine regions, one novel sterile source with less alien cytoplasm was discovered among 305 materials and named Bel CMS. The size of the alien cytoplasm in Bel CMS was 21,587 bp, accounting for 8.93% of its mtDNA, which was much less than that in Ogura CMS. Most importantly, the sterility gene orf138 was replaced by orf112, which had a 78-bp deletion, in Bel CMS. Interestingly, Bel CMS cabbage also maintained 100% sterility, although orf112 had 26 fewer amino acids than orf138. Field phenotypic observation showed that Bel CMS was an excellent sterile source with stable 100% sterility and no withered buds at the early flowering stage, which could replace Ogura CMS in cabbage heterosis utilization.

Comparative Transcriptome Analysis Reveals a Potential Regulatory Network for Ogura Cytoplasmic Male Sterility in Cabbage (Brassica oleracea L.)

“…At the full flowering stage, the newly opened flowers of the same day were removed, the petals and stamens were removed, the pollen was spread on a slide, and 2–3 drops of Alexander staining solution were added and mixed thoroughly. The slide was covered immediately, and the pollen was dyed for 3–6 h. Finally, the slides were observed under the microscope immediately after absorbing the excess liquid [ 67 ].…”

Mechanism and Utilization of Ogura Cytoplasmic Male Sterility in Cruciferae Crops

“…Apart from a 39-bp deletion and two single-nucleotide polymorphisms (SNPs), the o rf125 and orf138 genes share 100% sequence identity with each other, which means that these two genes are highly homologous. Kos CMS caused by orf125 and Ogura CMS caused by orf138 can both be fertility restored by the fertility restorer gene Rfo / Rfk [ 114 ]. Kazama et al (2019) knocked out the mitochondrial gene orf125 by mitoTALENs in rapeseed, and the hypothesis that orf125 is the driver of Kosena-type CMS was verified, which strongly suggested that the orf138 gene is the sterility gene of Ogura CMS [ 120 ].…”