Os03g0654600

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Annotated Information

Function

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Mutation

• As seen in the screening of stay-green mutants, nol-1, nol-2 and nol-3 showed the stay-green phenotype 7 days after dark incubation (DAD), in comparison to the wild-type, which showed full yellowing at this stage (Figure 1b). The leaves of nol-1 retained more greenness relative to the wildtype and did not turn yellow even at the very late stage of natural senescence (Figure 1c).

Figure 1. Mutation positions and the stay-green phenotype of nol mutants. .

• The change in chlorophyll content during dark-induced senescence was analyzed in nol-1, which showed prominent inhibition of Chl b degradation until 8 DAD (Figure 2a). Inhibition of Chl a degradation in nol-1 was not obvious until 4 DAD, but became significant at 6 DAD and thereafter. The ratio of Chl a to Chl b was close to 1 at 8 DAD. These characteristics were also observed in nol-2 and nol-3. As other parameters of leaf senescence, we measured the change in the Fv/Fm value (the ratio of variable to maximum fluorescence; a parameter of PSII activity) and membrane ion leakage during dark-induced senescence. The Fv/Fm value for nol-1 during dark-induced senescence decreased in a similar manner to the wild-type (Figure 2b), and membrane ion leakage also increased similarly to the wild-type (Figure 2c). These results indicate that nol shows the stay-green phenotype due to the retention of chlorophyll, but leaf functionality decreases during senescence.

Figure 2. Physiological characterization of nol-1 during senescence. (a) Change in the chlorophyll content during dark incubation. Chlorophyll was extracted with 80% acetone and its content was measured spectrophotometrically. Solid line, nol-1; dotted line, wild-type; closed circles, Chl a; open circles, Chl b. Bars indicate standard errors (n = 3). (b) Change in Fv/Fm values during dark incubation. Solid line, nol-1; dotted line, wild-type. Bars indicate standard errors (n = 3). (c) Change in membrane ion leakage during dark incubation. Solid line, nol-1; dotted line, wild-type. Bars indicate standard errors (n = 3). .

• To examine the behavior of the chlorophyll–protein complexes in nol mutants, we performed a ‘green-gel’ analysis (Figure 3a). The amounts of chlorophyll–protein complexes, namely the PSI reaction center, LHCII trimer, CP43/47, LHCI dimer and LHCII monomer, were similar between the wildtype and nol-1 before dark treatment. During dark-induced senescence, all chlorophyll–protein complexes were degraded in the wild-type, and the LHCII monomer and LHCII trimer were selectively retained in nol-1 (Figure 3a). Immunoblot analysis revealed that all LHCI proteins

examined, namely Lhca1, Lhca3 and Lhca4, and PsaF, a component of the PSI core complex, were degraded at the late stage of senescence in both wild-type and nol-1 (Figure 3b).

Figure 3. Protein degradation during senescence in nol-1, nyc1-2 and nol-1 nyc1-2. .

Expression

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Evolution

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Labs working on this gene

• Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, 113-8657, Japan,
• Institute of Radiation Breeding, National Institute of Agrobiological Sciences, Hitachi-ohmiya, 219-2293, Japan,
• The Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan, and
• Graduate School of Science, Hiroshima University, Higashi-hiroshima, 739-8526, Japan