Specific and multiple-target gene silencing reveals function diversity of BnaA2.NIP5;1 and BnaA3.NIP5;1 in Brassica napus.

Rapeseed (Brassica napus) is an economically important oilseed crop in the world, but its production is strongly dependent on boron (B) supplies. Major intrinsic protein NIP5;1 is essential for B uptake and plant development under B limitation. In this study, phylogenetic and expression analyses identified two NIP5;1 orthologue genes, BnaA2.NIP5;1 and BnaA3.NIP5;1, which are mainly expressed in roots of B. napus. Specific and multiple-target RNAi was used to suppress BnaA3.NIP5;1 or both BnaA2.NIP5;1 and BnaA3.NIP5;1 expression in B-efficient rapeseed Qingyou 10 (QY10), respectively, for revealing the roles of BnaA2.NIP5;1 and BnaA3.NIP5;1 in low-B tolerance in B. napus. We found that both BnaA2.NIP5;1 and BnaA3.NIP5;1 are important for B. napus normal growth under low-B conditions, while these two genes have distinct roles. BnaA2.NIP5;1 is mainly expressed in the epidermis cells, which is required for efficient B uptake into roots, hence for B translocation to the shoots. BnaA3.NIP5;1 is specifically localized in the distal part of lateral root cap cells to promoter root elongation under low-B conditions, which is important for seed production in the maturity stage of B. napus. Taken together, our specific and multiple-target RNAi strategy provides novel insights into the gene function diversification between BnaA2.NIP5;1 and BnaA3.NIP5;1, such an approach can be potentially applicable to other polyploid crops.