Genome-wide identification of the NPR1 -like gene family in Brassica napus and functional characterization of BnaNPR1 in resistance to Sclerotinia sclerotiorum

The BnaNPR1-like gene family was identified in B. napus, and it was revealed that repression of BnaNPR1 significantly reduces resistance to S. sclerotiorum, intensifies ROS accumulation, and changes the expression of genes associated with SA and JA/ET signaling in response to this pathogen. The NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1) and related NPR1-like genes play an important role in regulating plant defense. Oilseed rape (Brassica napus L.) is an important oilseed crop; however, little is known about the B. napus (Bna) NPR1-like gene family. Here, a total of 19 BnaNPR1-like genes were identified in the B. napus genome, and then named according to their respective best match in Arabidopsis thaliana (At), which led to the determination of B. napus homologs of every AtNPR1-like gene. Analysis of important protein domains and functional motifs indicated the conservation and variation among these homologs. Phylogenetic analysis of these BnaNPR1-like proteins and their Arabidopsis homologs revealed six distinct sub-clades, consequently indicating that their name classification totally conformed to their phylogenetic relationships. Further, B. napus transcriptomic data showed that the expression of three BnaNPR1s was significantly down-regulated in response to infection with Sclerotinia sclerotiorum, the most important pathogen of this crop, whereas BnaNPR2/3/4/5/6s did not show the expression differences in general. Further, we generated B. napus BnaNPR1-RNAi lines to interpret the effect of the down-regulated expression of BnaNPR1s on resistance to S. sclerotiorum. The results showed that BnaNPR1-RNAi significantly decreased this resistance. Further experiments revealed that BnaNPR1-RNAi intensified ROS production and changed defense responses in the interaction of plants with this pathogen. These results indicated that S. sclerotiorum might use BnaNPR1 to regulate specific physiological processes of B. napus, such as ROS production and SA defense response, for the infection.