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Auxin response factor 2 (ARF2) plays a major role in regulating auxin-mediated leaf longevity.

Lim PO, Lee IC, Kim J, Kim HJ, Ryu JS, Woo HR, Nam HG - J. Exp. Bot. (2010)

Bottom Line: It was found here that ARF2 functions in the auxin-mediated control of Arabidopsis leaf longevity, as discovered by screening EMS mutant pools for a delayed leaf senescence phenotype.Therefore, the ore14/arf2 lesion appears to cause reduced repression of auxin signalling with increased auxin sensitivity, leading to delayed senescence.Altogether, our data suggest that ARF2 positively regulates leaf senescence in Arabidopsis.

View Article: PubMed Central - PubMed

Affiliation: Department of Science Education, Jeju National University, 66 Jejudaehakno, Jeju, 690-756, Korea.

ABSTRACT
Auxin regulates a variety of physiological and developmental processes in plants. Although auxin acts as a suppressor of leaf senescence, its exact role in this respect has not been clearly defined, aside from circumstantial evidence. It was found here that ARF2 functions in the auxin-mediated control of Arabidopsis leaf longevity, as discovered by screening EMS mutant pools for a delayed leaf senescence phenotype. Two allelic mutations, ore14-1 and 14-2, caused a highly significant delay in all senescence parameters examined, including chlorophyll content, the photochemical efficiency of photosystem II, membrane ion leakage, and the expression of senescence-associated genes. A delay of senescence symptoms was also observed under various senescence-accelerating conditions, where detached leaves were treated with darkness, phytohormones, or oxidative stress. These results indicate that the gene defined by these mutations might be a key regulatory genetic component controlling functional leaf senescence. Map-based cloning of ORE14 revealed that it encodes ARF2, a member of the auxin response factor (ARF) protein family, which modulates early auxin-induced gene expression in plants. The ore14/arf2 mutation also conferred an increased sensitivity to exogenous auxin in hypocotyl growth inhibition, thereby demonstrating that ARF2 is a repressor of auxin signalling. Therefore, the ore14/arf2 lesion appears to cause reduced repression of auxin signalling with increased auxin sensitivity, leading to delayed senescence. Altogether, our data suggest that ARF2 positively regulates leaf senescence in Arabidopsis.

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Related in: MedlinePlus

Whole-plant phenotypes of Arabidopsis wild-type (‘Col’, left) and ore14-1 mutant (right) plants at 35, 46, and 65 d after germination (DAG).
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fig1: Whole-plant phenotypes of Arabidopsis wild-type (‘Col’, left) and ore14-1 mutant (right) plants at 35, 46, and 65 d after germination (DAG).

Mentions: Arabidopsis, a representative monocarpic plant, is a favoured model for molecular and genetic studies of leaf senescence because its leaves readily undergo easily distinguishable developmental stages and show a well-defined and reproducible senescence programme (Hensel et al., 1993). Arabidopsis populations mutagenized with EMS for delayed leaf senescence mutants were screened, which allowed us to identify positive elements of senescence. Initial screening was carried out by visual evaluation of the degree of yellowing caused by chlorophyll loss when detached leaves were incubated in the dark. This technique is widely used for the consistent acceleration of leaf senescence (Oh et al., 1997). One of the mutants, ore14-1, which exhibited a delayed leaf senescence phenotype, was selected for further study. This mutation has a pleiotropic effect on vegetative and reproductive development, including the increased growth of aerial organs, inhibited floral bud opening, late flowering, and a delay in stem senescence (Fig. 1). These traits co-segregated with the delayed leaf senescence phenotype (data not shown). Genetic segregation analysis of the senescence phenotype was performed in F1 and F2 progeny derived from crosses between wild-type plants and the ore14-1 mutant. All F1 plants had normal phenotypes, including senescence symptoms, demonstrating that the ore14-1 mutation is recessive. In the F2 generation, 99 plants exhibiting wild-type phenotypes and 29 mutant plants were scored, indicative of 3:1 segregation (χ2=0.37, P >0.05). This showed that the mutation is inherited as a monogenic recessive trait.


Auxin response factor 2 (ARF2) plays a major role in regulating auxin-mediated leaf longevity.

Lim PO, Lee IC, Kim J, Kim HJ, Ryu JS, Woo HR, Nam HG - J. Exp. Bot. (2010)

Whole-plant phenotypes of Arabidopsis wild-type (‘Col’, left) and ore14-1 mutant (right) plants at 35, 46, and 65 d after germination (DAG).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2837260&req=5

fig1: Whole-plant phenotypes of Arabidopsis wild-type (‘Col’, left) and ore14-1 mutant (right) plants at 35, 46, and 65 d after germination (DAG).
Mentions: Arabidopsis, a representative monocarpic plant, is a favoured model for molecular and genetic studies of leaf senescence because its leaves readily undergo easily distinguishable developmental stages and show a well-defined and reproducible senescence programme (Hensel et al., 1993). Arabidopsis populations mutagenized with EMS for delayed leaf senescence mutants were screened, which allowed us to identify positive elements of senescence. Initial screening was carried out by visual evaluation of the degree of yellowing caused by chlorophyll loss when detached leaves were incubated in the dark. This technique is widely used for the consistent acceleration of leaf senescence (Oh et al., 1997). One of the mutants, ore14-1, which exhibited a delayed leaf senescence phenotype, was selected for further study. This mutation has a pleiotropic effect on vegetative and reproductive development, including the increased growth of aerial organs, inhibited floral bud opening, late flowering, and a delay in stem senescence (Fig. 1). These traits co-segregated with the delayed leaf senescence phenotype (data not shown). Genetic segregation analysis of the senescence phenotype was performed in F1 and F2 progeny derived from crosses between wild-type plants and the ore14-1 mutant. All F1 plants had normal phenotypes, including senescence symptoms, demonstrating that the ore14-1 mutation is recessive. In the F2 generation, 99 plants exhibiting wild-type phenotypes and 29 mutant plants were scored, indicative of 3:1 segregation (χ2=0.37, P >0.05). This showed that the mutation is inherited as a monogenic recessive trait.

Bottom Line: It was found here that ARF2 functions in the auxin-mediated control of Arabidopsis leaf longevity, as discovered by screening EMS mutant pools for a delayed leaf senescence phenotype.Therefore, the ore14/arf2 lesion appears to cause reduced repression of auxin signalling with increased auxin sensitivity, leading to delayed senescence.Altogether, our data suggest that ARF2 positively regulates leaf senescence in Arabidopsis.

View Article: PubMed Central - PubMed

Affiliation: Department of Science Education, Jeju National University, 66 Jejudaehakno, Jeju, 690-756, Korea.

ABSTRACT
Auxin regulates a variety of physiological and developmental processes in plants. Although auxin acts as a suppressor of leaf senescence, its exact role in this respect has not been clearly defined, aside from circumstantial evidence. It was found here that ARF2 functions in the auxin-mediated control of Arabidopsis leaf longevity, as discovered by screening EMS mutant pools for a delayed leaf senescence phenotype. Two allelic mutations, ore14-1 and 14-2, caused a highly significant delay in all senescence parameters examined, including chlorophyll content, the photochemical efficiency of photosystem II, membrane ion leakage, and the expression of senescence-associated genes. A delay of senescence symptoms was also observed under various senescence-accelerating conditions, where detached leaves were treated with darkness, phytohormones, or oxidative stress. These results indicate that the gene defined by these mutations might be a key regulatory genetic component controlling functional leaf senescence. Map-based cloning of ORE14 revealed that it encodes ARF2, a member of the auxin response factor (ARF) protein family, which modulates early auxin-induced gene expression in plants. The ore14/arf2 mutation also conferred an increased sensitivity to exogenous auxin in hypocotyl growth inhibition, thereby demonstrating that ARF2 is a repressor of auxin signalling. Therefore, the ore14/arf2 lesion appears to cause reduced repression of auxin signalling with increased auxin sensitivity, leading to delayed senescence. Altogether, our data suggest that ARF2 positively regulates leaf senescence in Arabidopsis.

Show MeSH
Related in: MedlinePlus