Increased seed number per silique in Brassica juncea by deleting cis-regulatory region affecting BjCLV1 expression in carpel margin meristem

Mustard yield per plant is severely restricted by the seed number per silique. The seed number per silique in the Brassica juncea trilocular mutant J163-4 is significantly greater than that in normal bilocular plants. However, how the trilocular silique of J163-4 is formed remains unclear. Here, we studied the gene structure and function of mc2 in B. juncea and Arabidopsis using comparative morphology and molecular genetic experiments. We found that mc2 is a CLV1 ortholog, BjA7.CLV1. The deletion of cis-regulatory region in mc2 promoter, which affects Mc2 expression in carpel margin meristem (CMM), led to trilocular silique formation. The BjCLV1 sequence with its complete promoter containing the cis-regulatory region can restore the Bjclv1 and clv1 mutant phenotypes in B. juncea and Arabidopsis, respectively. Additionally, this cis-regulatory region had a collinear segment in the promoter of CLV1 homologous gene in most Brassicaceae species. Our results are consistent with the report that BjCLV1 represents a conserved pleiotropic role in shoot meristem and CMM development, which contains a cis-regulatory sequence specifically expressed BjCLV1 in CMM in its promoter, and this cis-regulatory region is conserved in Brassicaceae species. These results offer a reliable approach for fine-tuning the traits of seed yield in Brassicaceae crops.

Automated summary

Through comparative morphology and molecular genetic experiments, this study investigated the gene structure and function of mc2 in Brassica juncea and Arabidopsis. It was found that mc2 is a ortholog of CLV1, BjA7.CLV1, and its deletion in the cis-regulatory region in the promoter led to the formation of trilocular silique. The results suggest a conserved pleiotropic role of BjCLV1 in shoot meristem and CMM development, with a specific cis-regulatory region involved in its expression.