Development, characteristics, and gene expression profiles of a chromosomal deletion line of Brassica juncea (AABB, 2n=36) with apetalous feature derived from interspecific hybridization

Interspecific hybridization has been a crucial technique in improving genetic diversity and developing novel traits in cultivated plants. The apetalous Brassica juncea (AABB, 2n = 36) represents a valuable germplasm resource with highly desirable characteristics for breeding purposes. Nevertheless, apetalous germplasm resources in B. juncea are currently scarce. In this study, we successfully established a stable apetalous B. juncea (ABJ) line by crossing B. juncea “YLC” with B. carinata “Bc216” (BBCC, 2n = 34). Cytological analysis indicates that ABJ exhibited normal chromosome behavior, with 18 bivalents in diakinesis and an equal number of chromosome segregations at anaphase I in the pollen mother cells during meiosis. Fluorescence in situ hybridization (FISH) confirmed that the chromosome configuration of ABJ is similar to that of its parental line B. juncea, containing 20 chromosomes from A-subgenome and 16 chromosomes from B-subgenome constituting the chromosome number of 36. However, a 15.8 Mb deletion in chromosome A03 of ABJ was uncovered by RNA-seq and molecular markers. Twenty-four differentially expressed genes which may be associated with the regulation of ABJ's apetalous traits were identified by gene expression profiling. To our knowledge, there have been no other documented instances of producing apetalous mustard with missing chromosome segments through interspecific hybridization. Consequently, this study not only verifies the feasibility of generating apetalous mustard with missing chromosome segments through interspecific hybridization but also provides a new insight into the mechanisms underlying the formation of apetalous trait.