Genome-wide analysis of NAC gene family in Brassica campestris ssp. chinensis and characterization of BcNAC134.

Key message: 204 BcNAC genes were identified and 98 BcNACs were differentially expressed in leaves at four developmental stages. BcNAC134 directly activates BcSAG12 expression and silencing of BcNAC134 delayed leaf senescence. Leaf senescence is a key factor restricting the development of non-heading Chinese cabbage (NHCC, Brassica campestris (syn. Brassica rapa) ssp. chinensis), which resulted in decreased product quality and shortened harvest period. The NAC (NAM, ATAF1/2, and CUC2) family is plant-specific and involved in multiple developmental processes. In this study, a total of 204 BcNACs were identified based on the NHCC genome. These genes were unevenly distributed on 10 chromosomes and classified into 13 groups. A total of 10 conserved motifs were identified by gene structure and motif analysis, among which motifs 1-6 were highly conserved, while motifs 7-10 existed in only a few groups. RNA-seq and RT-qPCR results both indicated that 10 BcNACs were influenced by age-dependent leaf senescence. Further validation showed that silencing of BcNAC134 in NHCC resulted in delayed leaf senescence and was accompanied by down-regulation of senescence-associated genes (SAGs). BcNAC134 localized in the nucleus and had transcription activation activity. BcNAC134 could directly bind to and activate BcSAG12, indicating that BcNAC134 promotes leaf senescence by activating BcSAG12. These results provide a foundation for further understanding the role of BcNACs in leaf senescence.