Deciphering the molecular architecture of a candidate r-gene (bjuWRRI) product mediating white rust resistance in Brassica juncea

In this investigation, a three-dimensional model of a R-gene encoded product Bju WRRl which is known to play a role in white rust resistance in Brassicajuncea was developed to synthesize innovative ways for evolving white rust resistant cultivars. The model was built from the amino acid sequence of BjuWRR1 using structural template information of a disease resistance protein (RPP13-like protein 4 of Arabidopsis thaliana) with the help of homology-based modelling approach. Built models were validated for their stereochemical parameters and structural descriptors using Ramachandran plot analysis, protein structure analysis and ERRAT analysis. Structural analysis of BjuWRR1 model revealed that it is composed of three distinct domains namely a coiled-coil domain, a central NB-ARC nucleotide binding domain and a hypervariable leucine-rich repeat domain. Further, canonical conserved motifs such as P-loop, Kinase2-motif and HD-motif were found in the NB-ARC domain. The built model would help in understanding the molecular basis of plant-immunity against white rust pathogen by understanding the significance of inter-domain interactions in BuWRR1 in triggering the activation of downstream defense response against the white rust pathogen by promoting oligomerization of coiled-coil domains through stabilized hydrophobic interactions and interaction with NB-ARC domain. Presence of patches of charged residues in each domain of BjuWRR1 indicated their possible role in intra-molecular interaction with other domains. Therefore, this model can help in designing functional genomic studies to understand the role of intra-molecular interaction in BjuWRR1 to mediate resistance against white rust pathogen.