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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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ORE14 is auxin response factor 2 (ARF2). (A) Map-based cloning of ORE14. The number of recombination events between CAPS markers and the ORE14 locus (r) is shown; BAC, bacterial artificial chromosome; cM, centimorgan. (B) Schematic representation of ORE14 with positions of the ore14-1 and 14-2 mutations; B3, DNA binding domain; ARF, auxin response region; AUX/IAA, domain involved in dimerization with other ARFs or Aux/IAA.
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fig2: ORE14 is auxin response factor 2 (ARF2). (A) Map-based cloning of ORE14. The number of recombination events between CAPS markers and the ORE14 locus (r) is shown; BAC, bacterial artificial chromosome; cM, centimorgan. (B) Schematic representation of ORE14 with positions of the ore14-1 and 14-2 mutations; B3, DNA binding domain; ARF, auxin response region; AUX/IAA, domain involved in dimerization with other ARFs or Aux/IAA.

Mentions: The gene responsible for the ore14-1 mutation was identified by map-based cloning (Fig. 2A). An initial genetic mapping, with CAPS markers, located ORE14 close to the LFY locus on Chromosome 5. CAPS markers were also generated using the genomic sequences of bacterial artificial chromosome clones (Fig. 2A). Among 1391 F2 progeny, one and two recombinant chromosomes were observed for the markers MTG10-M and K22G18-A, respectively. These mapping data located ORE14 at approximately 0.03 cM and 0.07 cM from these respective markers (Fig. 2A). The wild-type and mutant nucleotide sequences for the region around the map location of ORE14 were then compared. A single base change in the ore14-1 mutant—a G to A substitution—was identified at position 1673 from the translational start of the gene At5g62000 (Fig. 2B), which encodes auxin response factor 2 (ARF2). This mutation was expected to result in a premature stop codon at position 558 (Trp→stop) in the ARF2 protein. The same region was then sequenced from the ore14-2 mutant and it was found that a mutation here led to an early termination of translation at position 115 (Arg→stop) (Fig. 2B). Although the levels of ARF2 transcript of both mutants were comparable to that of wild-type plants (data not shown), these mutations probably cause a complete loss of function through premature translation termination. We simultaneously investigated a T-DNA insertion line in the At5g62000 gene, Salk_041472 line (arf2-5). The arf2-5 plants also exhibited phenotypes similar to those with the ore14 mutation, including delayed leaf senescence (data not shown). Several arf2 alleles were previously identified and designated as arf2-1 to arf2-9 (Ellis et al., 2005; Schruff et al., 2006); the ore14-1 and ore14-2 alleles are arf2-10 and arf2-11, respectively.


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)

ORE14 is auxin response factor 2 (ARF2). (A) Map-based cloning of ORE14. The number of recombination events between CAPS markers and the ORE14 locus (r) is shown; BAC, bacterial artificial chromosome; cM, centimorgan. (B) Schematic representation of ORE14 with positions of the ore14-1 and 14-2 mutations; B3, DNA binding domain; ARF, auxin response region; AUX/IAA, domain involved in dimerization with other ARFs or Aux/IAA.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2: ORE14 is auxin response factor 2 (ARF2). (A) Map-based cloning of ORE14. The number of recombination events between CAPS markers and the ORE14 locus (r) is shown; BAC, bacterial artificial chromosome; cM, centimorgan. (B) Schematic representation of ORE14 with positions of the ore14-1 and 14-2 mutations; B3, DNA binding domain; ARF, auxin response region; AUX/IAA, domain involved in dimerization with other ARFs or Aux/IAA.
Mentions: The gene responsible for the ore14-1 mutation was identified by map-based cloning (Fig. 2A). An initial genetic mapping, with CAPS markers, located ORE14 close to the LFY locus on Chromosome 5. CAPS markers were also generated using the genomic sequences of bacterial artificial chromosome clones (Fig. 2A). Among 1391 F2 progeny, one and two recombinant chromosomes were observed for the markers MTG10-M and K22G18-A, respectively. These mapping data located ORE14 at approximately 0.03 cM and 0.07 cM from these respective markers (Fig. 2A). The wild-type and mutant nucleotide sequences for the region around the map location of ORE14 were then compared. A single base change in the ore14-1 mutant—a G to A substitution—was identified at position 1673 from the translational start of the gene At5g62000 (Fig. 2B), which encodes auxin response factor 2 (ARF2). This mutation was expected to result in a premature stop codon at position 558 (Trp→stop) in the ARF2 protein. The same region was then sequenced from the ore14-2 mutant and it was found that a mutation here led to an early termination of translation at position 115 (Arg→stop) (Fig. 2B). Although the levels of ARF2 transcript of both mutants were comparable to that of wild-type plants (data not shown), these mutations probably cause a complete loss of function through premature translation termination. We simultaneously investigated a T-DNA insertion line in the At5g62000 gene, Salk_041472 line (arf2-5). The arf2-5 plants also exhibited phenotypes similar to those with the ore14 mutation, including delayed leaf senescence (data not shown). Several arf2 alleles were previously identified and designated as arf2-1 to arf2-9 (Ellis et al., 2005; Schruff et al., 2006); the ore14-1 and ore14-2 alleles are arf2-10 and arf2-11, respectively.

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