Identifying the components in Spl11-mediated defense pathway and determining the relationship between Spl11 and other defense signaling genes in rice

Ubiquitination has recently been shown to be involved in programmed cell death (PCD) in plants. Spl11 encodes an E3 ubiquitin ligase with U-Box and ARM repeat domains which negatively regulates PCD and disease resistance in rice. To identify new components in Spl11-mediated cell death pathway, a suppressor screen was performed using the spl11 mutant GR5717 and EMS as a mutagen. The spontaneous lesion formation observed in GR5717 was found to be completely suppressed in one suppressor, whereas, two other suppressors showed partial suppression. Broad-spectrum resistance in GR5717 was found to be abolished in all the suppressors. To map the genes involved in this suppression phenomenon, three F2 mapping populations were generated using the suppressor lines and spl11 mutant line TP309spl11. All the three F2 populations show 3:1 ratio of segregation for suppression phenotype to lesion mimic phenotype, indicating a single-gene Mendelian inheritance. Simultaneously F2 populations are also being generated to test for diallelism among different suppressors. Further, genetic analysis to study the relationship between Spl11 and other defense signaling genes such as NPR1, SGT1, RAR1 and Rac1 has been undertaken. Crosses between spl11 knockdown or Spl11 overexpression lines and other defense mutants are being generated. Overall, ubiquitination mediated defense mechanisms will be elucidated through these studies in rice which is the world's most important food crop.