Genome-wide analysis of the JAZ subfamily and functional verification of BnC8.JAZ1-1 in Brassica napus

Abstract Background JAZ subfamily plays crucial roles in growth and development, stress, and hormone responses in various plant species. Despite its importance, the structural and functional analyses of the JAZ subfamily in Brassica napus are still limited. Results In relative to the 12 JAZ genes in Arabidopsis, there are 28, 31, and 56 JAZ orthologues in the genome of B. rapa, B. oleracea, and B. napus, respectively, in accordance with the proven triplication events during the evolution of Brassicaceae. The phylogenetic analysis showed that the 127 JAZ proteins from A. thaliana, B. rapa, B. oleracea, and B. napus could fall into 5 groups. The gene structure analysis of all 127 JAZs showed that these proteins have the common motifs of TIFY and Jas, indicating their conservation in Brassicaceae species. In addition, cis-element analysis showed that the main motif types are related to phytohormones, biotic and abiotic stresses. The qRT-PCR of the representative 11 JAZ genes in B. napus demonstrated that different groups of BnJAZ individuals have distinct patterns of expression in normal conditions or treatment with distinctive abiotic stresses and phytohormones. Specially, BnJAZ52 (BnC08.JAZ1-1) was significantly repressed by ABA, GA, IAA, PEG and NaCl treatments, while induced under MeJA, cold and waterlogging. Expression pattern analysis showed that BnC08.JAZ1-1 was expressed mainly in vascular bundle and young flower including petal, pistil, stamen and developing ovule, but not in stem, leaf and mature silique and seed. Subcellular localization showed that its protein was localized in the nucleus, in line with its orthologues in Arabidopsis. The further over-expression of BnC08.JAZ1-1 in Arabidopsis resulted in enhanced seed weight, likely through regulating the expression of the downstream response genes involved in the ubiquitin-proteasome pathway and phospholipid metabolism pathway. Conclusions The systematic identification, phylogenetic, syntenic, and expression analyses of the BnJAZs subfamily improve our understanding of their roles in responses to stress and phytohormone in B. napus. In addition, the preliminary functional validation of BnC08.JAZ1-1 in Arabidopsis demonstrated that this subfamily might also play a role in regulating seed weight.