Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 104, Issue 35, Pages 14169-14174Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0705521104
Keywords
locus; pea; rice; senescence; stay green
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Funding
- NCIRD CDC HHS [H23 IP001011] Funding Source: Medline
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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 (Chi a) and chlorophyll b (Chi b) content in the late stage of senescence, suggesting that SGR is primarily involved in Chi 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 Chi a and Chi b, respectively, was not affected by sgr in rice. The results suggest that SGR might be involved in activation of the Chi-degrading pathway during leaf senescence through translational or posttranslational regulation of Chl-degrading enzymes.
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