Constructed Rice Tracers Identify the Major Virulent Transcription Activator-Like Effectors of the Bacterial Leaf Blight Pathogen

Abstract

Xanthomonas oryzae pv. oryzae (Xoo) injects major transcription activator-like effectors (TALEs) into plant cells to activate susceptibility (S) genes for promoting bacterial leaf blight in rice. Numerous resistance (R) genes have been used to construct differential cultivars of rice to identify races of Xoo, but the S genes were rarely considered. Different edited lines of rice cv. Kitaake were constructed using CRISPR/Cas9 gene-editing, including single, double and triple edits in the effector-binding elements (EBEs) located in the promoters of rice S genes OsSWEET11a, OsSWEET13 and OsSWEET14. The near-isogenic lines (NILs) were used as tracers to detect major TALEs (PthXo1, PthXo2, PthXo3 and their variants) in 50 Xoo strains. The pathotypes produced on the tracers determined six major TALE types in the 50 Xoo strains. The presence of the major TALEs in Xoo strains was consistent with the expression of S genes in the tracers, and it was also by known genome sequences. The EBE editing had little effect on agronomic traits, which was conducive to balancing yield and resistance. The rice-tracers generated here provide a valuable tool to track major TALEs of Xoo in Asia which then shows what rice cultivars are needed to combat Xoo in the field.