IDENTIFYING THE MOLECULAR MECHANISMS OF BACTERIAL EFFECTOR PROTEINS FROM Xanthomonas oryzae pv. oryzae CAUSING LEAF BLIGHT DISEASE IN RICE AND USE OF SMALL MOLECULES IN DISEASE RESISTANCE

SWATHI, S. PATIL

IDENTIFYING THE MOLECULAR MECHANISMS OF BACTERIAL EFFECTOR PROTEINS FROM Xanthomonas oryzae pv. oryzae CAUSING LEAF BLIGHT DISEASE IN RICE AND USE OF SMALL MOLECULES IN DISEASE RESISTANCE

Date

2023-05-05

Authors

SWATHI, S. PATIL

Publisher

University of Agricultural Sciences, Bangalore

Abstract

Rice (Oryza sativa L.) is the most important staple commodity, providing food for nearly half the global population. The bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive diseases afflicting rice fields. The morphological, biochemical and pathogenicity characteristics of ten Xoo isolates from various rice-growing regions in India were used to differentiate them. The pathogenicity assay determined that all isolates were virulent on the susceptible variety TN-1, with the KA isolate producing significantly more lesion length, in planta bacterial count, xanthomonadin, and exopolysaccharide. Through dual transcriptome analysis of contrasting rice cultivars (TN-1 and RP-Bio226), disease resistance genes such as ARK1AS, mla1, RPM1, RPS2 and RPP-13 protein 1 were found to be upregulated in RP-Bio226 in response to Xoo infection. In the susceptible variety, the production of the susceptibility gene OsSWEET11 was upregulated, whereas it was downregulated in the resistant cultivar RP-Bio226. Many type 3 secretion system proteins, including PthXo1, XopN, XopW, HrpB2, SctJ, and SctN were identified in Xoo infecting the susceptible variety, but none in the resistant variety. RP-Bio226 produced higher levels of hydrogen peroxide and superoxide anion than the susceptible variety TN-1. Using plants expressing OsSWEET11- gRNA, the OsSWEET11 gene was characterised using the CRISPR Cas9 gene editing technology. Gene editing was confirmed in the transgenic plant S21 with change in amino acid from isoleucine to leucine at position 263 and leucine to isoleucine at position 266. S21 also displayed a resistant reaction to Xoo. In addition, a novel small molecule 6-[(3- oxido-2,1,3-benzoxadiazol-3-ium-5-yl)oxy]2,1,3-benzoxadiazol-1-ium-1-olate was identified through a chemical genomics approach, targeting the effector protein PthXo1 to confer resistance against Xoo in the TN-1 variety. The plants sprayed with the small molecule immediately following Xoo inoculation exhibited a significant decrease in lesion length and in planta bacterial count compared to the control.