Phylogenetic Analyses of Citrus LRR-RLKs

Citrus is one of the most important commercial and nutritional fruit crops. Nonetheless, susceptibility to many pathogens has affected its productivity around the world. The advent of powerful genomic tools and the available citrus genome sequences allowed several studies focusing the molecular processes related with molecular citrus-pathogen interactions. Due to the importance of plant receptors in plant-pathogen perception and response, we proposed to study the Leucine-rich repeat receptor-like kinases (LRR-RLKs) in Citrus. The LRR-RLKs constitute the largest group of RLKs in plants and play important roles in a wide variety of processes related to development and defense. We used 48 representative RLK protein sequences from Arabidopsis to conduct batch BLASTp searches against the predicted proteins of Citrus clementina (clementine mandarin) and C. sinensis (sweet orange). Preliminary analysis revealed 319 and 315 LRR RLKs members from clementina and sweet orange, respectively. The kinase domain from citrus, Arabidopsis and rice were aligned using ClustalX. Phylogenetic tree was constructed in MEGA5 using neighbor-joining method, the Poisson correction model, pairwise deletion and bootstrap analysis performed with 500 replicates. The results showed that many sequences of LRR-RLKs from clementine and sweet orange were grouped with the Arabidopsis and rice counterparts, with well-supported clades, indicating a good correspondence between LRR-RLKs of these species. However, some sequences of citrus do not cluster with any of the LRR-RLK groups previously described for Arabidopsis and rice, and these clades could represent a species-specific divergence between sub-groups of LRR-RLKs of citrus.

Financial support: INCT-Citrus/ CNPq/Fapesp