NYC4 , the rice ortholog of Arabidopsis THF1 , is involved in the degradation of chlorophyll – protein complexes during leaf senescence

Summary Yellowing/chlorophyll breakdown is a prominent phenomenon in leaf senescence, and is associated with the degradation of chlorophyll – protein complexes. From a rice mutant population generated by ionizing radiation, we isolated nyc4‐1 , a stay‐green mutant with a defect in chlorophyll breakdown during leaf senescence. Using gene mapping, nyc4‐1 was found to be linked to two chromosomal regions. We extracted Os07g0558500 as a candidate for NYC4 via gene expression microarray analysis, and concluded from further evidence that disruption of the gene by a translocation‐related event causes the nyc4 phenotype. Os07g0558500 is thought to be the ortholog of THF1 in Arabidopsis thaliana . The thf1 mutant leaves show variegation in a light intensity‐dependent manner. Surprisingly, the F v / F m value remained high in nyc4‐1 during the dark incubation, suggesting that photosystem II retained its function. Western blot analysis revealed that, in nyc4‐1 , the PSII core subunits D1 and D2 were significantly retained during leaf senescence in comparison with wild‐type and other non‐functional stay‐green mutants, including sgr‐2 , a mutant of the key regulator of chlorophyll degradation SGR. The role of NYC4 in degradation of chlorophyll and chlorophyll – protein complexes during leaf senescence is discussed.