AUXIN RESPONSE FACTOR1andAUXIN RESPONSE FACTOR2regulate senescence and floral organ abscission inArabidopsis thaliana

Abstract

In plants, both endogenous mechanisms and environmental signals regulate developmental transitions such as seed germination, induction of flowering,leaf senescence and shedding of senescent organs. Auxin response factors(ARFs) are transcription factors that mediate responses to the plant hormone auxin. We have examined Arabidopsis lines carrying T-DNA insertions in AUXIN RESPONSE FACTOR1 (ARF1) and ARF2 genes. We found that ARF2 promotes transitions between multiple stages of Arabidopsis development. arf2 mutant plants exhibited delays in several processes related to plant aging, including initiation of flowering, rosette leaf senescence, floral organ abscission and silique ripening. ARF2 expression was induced in senescing leaves. ARF2 regulated leaf senescence and floral organ abscission independently of the ethylene and cytokinin response pathways. arf1 mutations enhanced many arf2 phenotypes, indicating that ARF1 acts in a partially redundant manner with ARF2. However, unlike arf2mutations, an arf1 mutation increased transcription of Aux/IAA genes in Arabidopsis flowers, supporting previous biochemical studies that indicated that ARF1 is a transcriptional repressor. Two other ARF genes, NPH4/ARF7 and ARF19, were also induced by senescence,and mutations in these genes enhanced arf2 phenotypes. NPH4/ARF7 and ARF19 function as transcriptional activators, suggesting that auxin may control senescence in part by activating gene expression.

Transcription Analysis of Arabidopsis Membrane Transporters and Hormone Pathways during Developmental and Induced Leaf Senescence

“…AtARF5 has not been assigned a role in senescence yet. Recently, regulation of leaf senescence by AtARF1 and 2 and a weak transcriptional repression/induction of AtARF1/AtARF2 during senescence have been observed (Lin and Wu, 2004;Ellis et al, 2005). In our experiments also, a 2-to 3-fold decrease/increase in AtARF1/AtARF2 expression can be seen, albeit below the significance threshold.…”

“…However, auxin treatment leads to a transient decrease in SAG12 expression (Noh and Amasino, 1999). Recently, it was described that the AUXIN RESPONSE FACTORs 1 and 2 (AtARF1 and AtARF2) are involved in regulation of abscission and senescence (Ellis et al, 2005;Okushima et al, 2005). More than 110 proteins implicated in auxin biosynthesis, metabolism, transport, and signaling were compiled from Woodward and Bartel (2005), Remington et al (2004), The Arabidopsis Information Resource Gene Ontologies, and gene descriptions (Supplemental Table XIV).…”

Functional Genomic Analysis of theAUXIN/INDOLE-3-ACETIC ACIDGene Family Members inArabidopsis thaliana [W]

“…A number of single lossof-function mutants have been isolated during the past 10 years, such as arf2/hss, arf3/ettin, arf5/mp, and arf7/nonphototropic hypocotyl4/msg1, which result in distinct developmental defects (Sessions et al, 1997;Hardtke and Berleth, 1998;Harper et al, 2000;Okushima et al, 2005). In addition, ARF double mutants have strong and visible phenotypes (Hardtke et al, 2004;Ellis et al, 2005;Okushima et al, 2005;Wang et al, 2005;Weijers et al, 2005;Wilmoth et al, 2005;H. Quach and A. Theologis, unpublished data).…”

SAUR36, a SMALL AUXIN UP RNA Gene, Is Involved in the Promotion of Leaf Senescence in Arabidopsis

“…Furthermore, several auxin response factor genes, such as ARF1, ARF2, ARF7, and ARF19, are expressed in senescing leaves in Arabidopsis. The T-DNA knockout arf2 mutant exhibits a delay in leaf senescence, and the delay in senescence becomes more striking in the arf1arf2 double mutant plants (Ellis et al, 2005). Most recently, a SenescenceAssociated Receptor-Like Kinase (SARK) from soybean (Glycine max) and its ortholog in Arabidopsis have been shown to promote leaf senescence, and auxin (and ethylene) biosynthesis and signaling pathways are required for SARK to cause leaf senescence .…”