IBR5, a Dual-Specificity Phosphatase-Like Protein Modulating Auxin and Abscisic Acid Responsiveness in Arabidopsis

Abstract

Auxin is an important plant hormone that plays significant roles in plant growth and development. Although numerous auxin-response mutants have been identified, auxin signal transduction pathways remain to be fully elucidated. We isolated ibr5 as an Arabidopsis indole-3-butyric acid-response mutant, but it also is less responsive to indole-3-acetic acid, synthetic auxins, auxin transport inhibitors, and the phytohormone abscisic acid. Like certain other auxin-response mutants, ibr5 has a long root and a short hypocotyl when grown in the light. In addition, ibr5 displays aberrant vascular patterning, increased leaf serration, and reduced accumulation of an auxin-inducible reporter. We used positional information to determine that the gene defective in ibr5 encodes an apparent dual-specificity phosphatase. Using immunoblot and promoterreporter gene analyses, we found that IBR5 is expressed throughout the plant. The identification of IBR5 relatives in other flowering plants suggests that IBR5 function is conserved throughout angiosperms. Our results suggest that IBR5 is a phosphatase that modulates phytohormone signal transduction and support a link between auxin and abscisic acid signaling pathways.

DEXH Box RNA Helicase–Mediated Mitochondrial Reactive Oxygen Species Production in Arabidopsis Mediates Crosstalk between Abscisic Acid and Auxin Signaling

“…A study of ABA-potentiating auxin-mediated repression of embryonic axis elongation suggests that ABA enhances auxin signaling rather than increasing auxin flow or auxin levels (Belin et al, 2009). The auxin signaling-defective mutants axr1 and axr2 have reduced sensitivity to ABA during root elongation (Wilson et al, 1990;Tiryaki and Staswick, 2002;Monroe-Augustus et al, 2003). In another study, transgenic plants overexpressing the H 2 O 2 -inducible gene UGT74E2, which encodes an indole-3-butyric acid (IBA) glucosyltransferase, had elevated levels of both IBA-Glc and free IBA (IAA precursor) and Four-day-old seedlings were transferred to MS medium (Con) or MS medium containing 30 mM ABA, 600 mM GSH, 2.5 mM BSO, 30 mM ABA plus 600 mM GSH, or 30 mM ABA plus 2.5 mM BSO for 2 d before being photographed with a confocal microscope with the same settings.…”

MicroRNA-Directed Regulation of ArabidopsisAUXIN RESPONSE FACTOR17Is Essential for Proper Development and Modulates Expression of Early Auxin Response Genes

“…5mARF17 Plants Respond to Auxin Treatment 5mARF17 plants have fewer lateral roots and shorter hypocotyls than control plants ( Figure 4M), traits characteristic of auxinresistant mutants (Estelle and Somerville, 1987;Hobbie and Estelle, 1995;Monroe-Augustus et al, 2003). 5mARF17 plants also have shorter primary roots than control plants ( Figure 4M), whereas auxin-resistant mutants typically have increased root length (Estelle and Somerville, 1987;Hobbie and Estelle, 1995;Monroe-Augustus et al, 2003).…”

“…5mARF17 plants also have shorter primary roots than control plants ( Figure 4M), whereas auxin-resistant mutants typically have increased root length (Estelle and Somerville, 1987;Hobbie and Estelle, 1995;Monroe-Augustus et al, 2003). To determine if the response to exogenous auxin was altered in 5mARF17 plants, we measured root and hypocotyl length after exposing plants to the auxin IAA.…”

Signal processing by protein tyrosine phosphorylation in plants

“…The ibr5 Arabidopsis mutant which is impaired in a DsPTP gene, is less sensitive to auxin and exhibits the characteristics of some auxin mutants such as a long root and a short hypocotyl when grown in light, fewer lateral roots, aberrant vascular patterning and an increased leaf serration. 113 In a proteomic study, Tyr phosphorylation of the auxin receptor, TIR1, has been reported in reference 35. The double mutant ibr5/tir1 enhances auxin resistance compound compared to that of either parent.…”

“…Involvement of Tyr phosphorylation have been observed in ABA signaling as the DsPTP PHS1 is a negative regulator of ABA transduction pathway whereas IBR5, another DsPTP, has been shown to regulate positively this pathway. 109,113 Moreover, Tyr phosphorylation controls both oxidative stress tolerance and the response to genotoxic stress. Reactive oxygen species are produced during the normal operation of respiratory and photosynthetic electron transport.…”