Identification and characterization of rice mutants that suppress XA21-mediated immunity by combining forward genetics and genomics approaches
F. LIU (1), M. Chern (1), W. Zhang (1), R. Jain (1), P. Ronald (1) (1) UC Davis, U.S.A.

The XA21 gene encodes a pattern recognition receptor, representative of a large group of receptor kinases in both plants and animals that are presumed to perceive signals through the extracellular domain and transduce the signal through the intracellular kinase. XA21 confers robust resistance to pathogen Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of rice bacterial blight. To identify components critical for XA21-mediated immunity, we carried out a forward genetic screen for rice mutants that suppress the XA21-mediated immunity by inoculating individual plants of a fast neutron-induced rice mutant population established in a Kitaake rice line carrying the Ubi-XA21 gene. We have obtained 10 suppressors of XA21-mediated immunity (sxi) after screening approximately 21,000 M2 (about 3,000 M1) plants. I have confirmed and characterized two of these mutants by backcrossing to the Ubi-XA21 parent and inoculating the F1 plants and F2 progeny with Xoo. One mutant appeared as recessive and the other behaved as a dominant mutation. To identify the locus that is responsible for the mutant phenotype, I have used a whole genome re-sequencing approach to reveal candidate mutations. A translocation was found associated with the recessive mutant (sxi3) phenotype and another insertion associated with the dominant mutant (sxi4) after analysis of a segregating F2 progeny population for co-segregation of the phenotype with the mutation. The translocation in mutant sxi3 knocked out a single candidate gene; sxi3 also severely affected plant growth, which co-segregated with the sxi3 phenotype. Furthermore, I was able to restore the sxi4 mutant to the parental resistant phenotype by silencing a candidate gene in sxi4, suggesting that this gene is responsible for sxi4. Neither gene has been reported to be involved in plant immunity to bacterial pathogen.

Abstract Number: P17-564
Session Type: Poster