Differential response of resistant gene analogues (RGAs) against Phytophthora colocasiae causing leaf blight in taro (Colocasia esculenta)

Abstract

Taro (Colocasia esculenta (L.) Schott.), an important tropical tuber crop with high nutritive, and medicinal potential, is ranked fourteen among the most consumed vegetable worldwide. Leaf blight caused by Phytophthora colocasiae, is one of the most destructive diseases of taro leads to severe yield loss up to 30-50%. The main objective of this study was the gene expression profiling of resistant gene analogues (RGAs) in resistant and susceptible taro cultivars upon leaf blight infection. For isolating the taro RGAs, PCR-based strategy with degenerate primers was used, and the obtained sequences showed similarity with other RGA sequences in the NCBI database, which categorised them into the NBS-LRR class of gene family. The conserved domain search has proved the presence of Nucleotide Binding-ARC domain in all the sequences. A phylogenetic tree constructed with the obtained taro RGAs and RGAs of other plant species in the database grouped them into the non-toll interleukin receptor (non-TIR) subclass of NBS sequences. RGA specific primer was designed based on sequence information, which is the first report in taro. The expression profiles of RGAs in Muktakeshi (resistant) and Sree Kiran (susceptible) genotypes in response to leaf blight infection determined by the SYBR green PCR assay demonstrated that, taro RGAs were up-regulated during the course of infection in both the resistant and susceptible cultivars. The normalized gene expression had shown a noticeable hike in the sample collected after 24 h of pathogen inoculation in the resistant variety, whereas in the susceptible variety it was observed at 36 h. Although, RGAs were expressed in both resistant and susceptible control plants, increased fold change was observed in the test plants following pathogen inoculation. The relative gene expression level of resistant and susceptible varieties was studied by using 2-ΔΔCT method and actin was used as the reference gene. These RGAs could be used as a good start point for further studies such as candidate gene mapping for taro leaf blight.