Mapping-based Cloning And Functional Analysis Of COI1 Suppressor, COS1 Gene In Arabidopsis

The Arabidopsis COI1 gene encodes an F-box protein to assemble SCFCOI1 complexes that are essential for responses to jasmonate (JA). Null mutations in COI1 abolish all the JA responses and exhibit resistance to JA-inhibition of plant growth, defect in pollen fertility, retard in senescence and susceptibility to pathogen infection and insect attack. To better understand the molecular mechanism via which COI1 regulates JA responses, we screened for suppressors of coil and isolated a cosl (coil suppressor 1) mutant. In the coil background, the cosl mutation restores the coil-related mutant phenotypes including defects in JA sensitivity, senescence and plant defense responses. The COS1 gene was cloned and found to encode a lumazine synthase, a key component in riboflavin pathway that is essential for diverse yet critical cellular processes, and also serve a variety of other roles such as DNA photo-repair, light sensing and bioluminescence. At the same times, cosl mutant constitutively expresses the senescence marker genes SEN4 and SAG12, indicates that COS1 gene may have a novel role in plant senescence. The G238A point mutation in cosl mutant abolished the splicing recognition sequence (from TA/GG to TA/AG), the TA/GC sequence located 18 bp downstream of G238A mutation serves as a new RNA splicing recognition site resulting in a 18-nucleotide deletion in the mutant cosl cDNA. We demonstrated a novel function of the riboflavin pathway in JA signal transduction and speculate that the riboflavin pathway acts downstream of COI1 and is required for suppression of the COI1-mediated root growth, senescence and plant defense.