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

Abstract

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 Fv /Fm 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.

The De-Etiolated 1 Homolog of Arabidopsis Modulates the ABA Signaling Pathway and ABA Biosynthesis in Rice

“…Thus, it appears that ABA signaling is intensified in OsDET1 RNAi plants during dark-induced leaf senescence. However, while the increased dark-induced leaf senescence phenotype is usually closely linked with premature leaf senescence in rice (Morita et al, 2009;Rong et al, 2013;Yamatani et al, 2013;Liang et al, 2014), in this study, OsDET1 deficiency accelerated darkinduced leaf senescence, but no visible difference in leaf senescence was observed in OsDET1 RNAi plants compared with wild-type plants at the vegetative and late filling stages ( Fig. 2; Supplemental Fig.…”

“…2, F-H;Supplemental Fig. S1, A and B;Morita et al, 2009;Rong et al, 2013;Yamatani et al, 2013;Liang et al, 2014).…”

Chlorophyll b degradation by chlorophyll b reductase under high-light conditions

“…This interconversion of chlorophyll a and chlorophyll b is called the chlorophyll cycle, which is believed to facilitate the regulation of the chlorophyll composition in a fluctuating light environment and throughout developmental stages. Recently, the analysis of a stay-green mutant demonstrates that the destabilization of a chlorophyll-protein complex participates in chlorophyll degradation (Christ and Hörtensteiner 2013;Yamatani et al 2013;Huang et al 2013). Chlorophyll b degradation might be regulated by certain destabilizing components in addition to CBR.…”

The Chloroplastic Protein THF1 Interacts with the Coiled-Coil Domain of the Disease Resistance Protein N′ and Regulates Light-Dependent Cell Death

“…Recently, Arabidopsis and rice (Oryza sativa) homologs of THF1 have been reported to regulate leaf senescence, a developmentally controlled form of programmed cell death Yamatani et al, 2013). In addition, at least two pathogen toxins target THF1 to promote infection, namely the necrotizing toxin ToxA from the wheat (Triticum aestivum) fungal pathogen P. tritici-repentis (Manning et al, 2007(Manning et al, , 2010 and COR from the bacterial pathogen P. syringae (Wangdi et al, 2010).…”

“…THF1 is a chloroplastic protein, but it is encoded by a nuclear gene that is conserved in all oxygenic photoautotrophs, from cyanobacteria to flowering plants (Wang et al, 2004;Keren et al, 2005). The THF1 protein was first identified in photosystem II (PSII) preparations of the cyanobacterium Synechocystis sp PCC 6803 (Kashino et al, 2002) and appears to interact with and regulate PSII components Yamatani et al, 2013). THF1 has also been shown to be involved in plant-pathogen interactions, as it is a direct target of the phytotoxin ToxA, a cell death-inducing protein of the necrotroph Pyrenophora tritici-repentis (Manning et al, 2007(Manning et al, , 2010.…”