Mendel's green cotyledon gene encodes a positive regulator of the chlorophyll-degrading pathway.
Mutants that retain greenness of leaves during senescence are known as "stay-green" mutants. The most famous stay-green mutant is Mendel's green cotyledon pea, one of the mutants used in determining the law of genetics. Pea plants homozygous for this recessive mutation (known as i at present) retain greenness of the cotyledon during seed maturation and of leaves during senescence. We found tight linkage between the I locus and stay-green gene originally found in rice, SGR. Molecular analysis of three i alleles including one with no SGR expression confirmed that the I gene encodes SGR in pea. Functional analysis of sgr mutants in pea and rice further revealed that leaf functionality is lowered despite a high chlorophyll a (Chl a) and chlorophyll b (Chl b) content in the late stage of senescence, suggesting that SGR is primarily involved in Chl degradation. Consistent with this observation, a wide range of Chl-protein complexes, but not the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit, were shown to be more stable in sgr than wild-type plants. The expression of OsCHL and NYC1, which encode the first enzymes in the degrading pathways of Chl a and Chl b, respectively, was not affected by sgr in rice. The results suggest that SGR might be involved in activation of the Chl-degrading pathway during leaf senescence through translational or posttranslational regulation of Chl-degrading enzymes.
Sato
Yutaka
Y
Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan.
Morita
Ryouhei
R
Nishimura
Minoru
M
Yamaguchi
Hiroyasu
H
Kusaba
Makoto
M
D002734:Chlorophyll / Q000378:metabolism*; D018548:Cotyledon / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D006706:Homeostasis; D008564:Membrane Potentials / Q000502:physiology; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D018532:Pisum sativum / Q000235:genetics; D010788:Photosynthesis; D018515:Plant Leaves / Q000235:genetics
D002734:Chlorophyll
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