Expression Analysis of Ossweet Genes Induced by xa13 Compatible Xanthomonas oryzae pv oryzae Isolates

Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv oryzae (Xoo) is a devastating disease responsible for major yield losses in irrigated rice growing regions of Asia. Xoo interacts with rice in a gene -for- gene manner dictated by virulence (vir)/avirulence (avr) genes in the pathogen and susceptibility(S)/ resistance(R) genes in the host. Members of the large transcription activator- like (TAL) effector family form the key virulence factors of Xoo, which reprogram host cells by mimicking eukaryotic transcription factors. In India, xa13, a recessive resistance gene, is predominantly deployed singly and in combination with xa5 and Xa21 to provide effective resistance to BLB. Owing to the race specific nature of the pathogens, even xa13 mediated resistance is getting defeated. It has been seen that Xoo isolates from Japan, Korea, Phillipines and Africa, carrying any one of the TAL effectors AvrXa7, PthXo2, PthXo3 or Tal5 induce expression of the S gene, Os11N3/SWEET14 to circumvent xa13 mediated resistance. We set to determine, which susceptibility genes facilitate BLB in response to infection by xa13 compatible Xoo isolates from India. RNA was extracted from artificially infected rice leaves with four different xa13 compatible Xoo isolates and used for cDNA synthesis. The expression of five SWEET/nodulin-3 genes predicted to be sugar transporters was analysed by reverse transcriptase PCR. We found that all the four Xoo isolates target one S gene, OsSWEET14. A comparative quantitative real time PCR between mock and infected rice cDNA further confirmed our results as an increase in OsSWEET14 expression was detected in the infected sample. Identification of the effector binding element regions in OsSWEET14 for the TALes from the four Xoo isolates is underway, which will be targeted for silencing.