Poster: Hormones

Abs # 633: IBR5, a novel phosphatase-like protein implicated in phytohormone signal transduction

Presenter:	Monroe-Augustus, Melanie , melaniem@bioc.rice.edu
Authors	Monroe-Augustus, Melanie  (A)   Zolman, Bethany K. (A)   Bartel, Bonnie  (A)
Affiliations:	(A): Rice University

Auxin is an important hormone that plays significant roles in plant growth and development, influencing apical dominance, vascularization, hypocotyl elongation, lateral root initiation, and tropisms. We are screening for mutants resistant to the inhibitory effects of auxin on root elongation to help elucidate the molecular mechanisms underpinning auxin signaling. ibr5was isolated as an indole-3-butyric acid (IBA)-response mutant but is resistant to the entire family of auxins, including indole-3-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D), and 1-naphthaleneacetic acid. Like certain other auxin-response mutants, ibr5has a long root and a short hypocotyl. In addition, ibr5displays aberrant leaf structure and reduced accumulation of an auxin-inducible reporter. ibr5also is resistant to the inhibitory effects of certain other phytohormones, including abscisic acid. Using positional information, we cloned the gene defective in ibr5,which encodes an apparent dual-specificity phosphatase. An IBR5promoter-GUS fusion is expressed in shoot and root meristems, cotyledons, true leaves, filaments, sepals, and pollen. IBR5 protein accumulates in leaves, flowers, stems, and siliques, and an IBR5 antibody does not detect IBR5 protein in the mutant. Our results suggest that IBR5 is a phosphatase acting in phytohormone signal transduction. Ongoing identification of proteins that genetically or physically interact with IBR5 will help decipher the roles of IBR5 in plant growth and development.