Morphological and genetic characterization of a new cytoplasmic male sterility system (oxa CMS) in stem mustard (Brassica juncea)
oxa CMS is a new cytoplasmic male sterility type in Brassica juncea.
oxa CMS is a cytoplasmic male sterility (CMS) line that has been widely used in the production and cultivation of stem mustard in the southwestern China. In this study, different CMS-type specific mitochondrial markers were used to confirm that oxa CMS is distinct from the pol CMS, ogu CMS, nap CMS, hau CMS, tour CMS, Moricandia arvensis CMS, orf220-type CMS, etc., that have been previously reported in Brassica crops. Pollen grains of the oxa CMS line are sterile with a self-fertility rate of almost 0% and the sterility strain rate and sterility degree of oxa CMS is 100% due to a specific flower structure and flowering habit. Scanning electron microscopy revealed that most pollen grains in mature anthers of the oxa CMS line are empty, flat and deflated. Semi-thin section further showed that the abortive stage of anther development in oxa CMS is initiated at the late uninucleate stage. Abnormally vacuolated microspores caused male sterility in the oxa CMS line. This cytological study combined with marker-assisted selection showed that oxa CMS is a novel CMS type in stem mustard (Brassica juncea). Interestingly, the abortive stage of oxa CMS is later than those in other CMS types reported in Brassica crops, and there is no negative effect on the oxa CMS line growth period. This study demonstrated that this novel oxa CMS has a unique flower structure with sterile pollen grains at the late uninucleate stage. Our results may help to uncover the mechanism of oxa CMS in Brassica juncea.
We sincerely thank researcher Yonghong Fan for his kindly provide the seeds of the stem mustard “Fuza 2”. This research was supported by China Agriculture Research System (CARS-24-A-06); the Fundamental Research Funds for the Central Universities (2662016PY106); the project of modern agricultural industry technology system of national characteristic vegetables and Nanhu Scholars Program for Young Scholars of XYNU. The authors are grateful to the anonymous reviewers for their constructive comments for revisions.
Compliance with ethical standards
Sequence data from this article can be found in the GenBank/EMBL data libraries under the following accession numbers: atp6 (BAC98864), orf224 (AAA32982), orf222 (NC_008285), orf138 (CAA78273), orf220 (AY208898), orf263 (X83692), and orf108 (EF483941). orf288 can be found in the supplemental data of reference Jing et al. (2012).
Conflict of interest
The authors declare that they have no conflict of interest.
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