title: Alternative splicing of Arabidopsis IBR5 pre-mRNA generates two IBR5 isoforms with distinct and overlapping functions.
abstract: The INDOLE-3-BUTYRIC ACID RESPONSE5 (IBR5) gene encodes a dual specificity phosphatase that regulates plant auxin responses. IBR5 has been predicted to generate two transcripts through alternative splicing, but alternative splicing of IBR5 has not been confirmed experimentally. The previously characterized ibr5-1 null mutant exhibits many auxin related defects such as auxin insensitive primary root growth, defective vascular development, short stature and reduced lateral root development. However, whether all these defects are caused by the lack of phosphatase activity is not clear. Here we describe two new auxin insensitive IBR5 alleles, ibr5-4, a catalytic site mutant, and ibr5-5, a splice site mutant. Characterization of these new mutants indicates that IBR5 is post-transcriptionally regulated to generate two transcripts, AT2G04550.1 and AT2G04550.3, and consequently two IBR5 isoforms, IBR5.1 and IBR5.3. The IBR5.1 isoform exhibits phosphatase catalytic activity that is required for both proper degradation of Aux/IAA proteins and auxin-induced gene expression. These two processes are independently regulated by IBR5.1. Comparison of new mutant alleles with ibr5-1 indicates that all three mutant alleles share many phenotypes. However, each allele also confers distinct defects implicating IBR5 isoform specific functions. Some of these functions are independent of IBR5.1 catalytic activity. Additionally, analysis of these new mutant alleles suggests that IBR5 may link ABP1 and SCF(TIR1/AFBs) auxin signaling pathways.
authors.affiliation: Department of Biology, Texas State University, San Marcos, Texas, United States of America.
authors.forename: Thilanka
authors.initials: T
authors.lastname: Jayaweera
authors.affiliation: Department of Biology, Texas State University, San Marcos, Texas, United States of America; Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma, United States of America.
authors.forename: Chamindika
authors.initials: C
authors.lastname: Siriwardana
authors.affiliation: Department of Biology, Texas State University, San Marcos, Texas, United States of America.
authors.forename: Sunethra
authors.initials: S
authors.lastname: Dharmasiri
authors.affiliation: Department of Plant Biology, University of Minnesota, St. Paul, Minnesota, United States of America; Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry, Halle (Saale), Germany.
authors.forename: Marcel
authors.initials: M
authors.lastname: Quint
authors.affiliation: Department of Plant Biology, University of Minnesota, St. Paul, Minnesota, United States of America.
authors.forename: William M
authors.initials: WM
authors.lastname: Gray
authors.affiliation: Department of Biology, Texas State University, San Marcos, Texas, United States of America.
authors.forename: Nihal
authors.initials: N
authors.lastname: Dharmasiri
mesh_terms: D000483:Alleles; D017398:Alternative Splicing / Q000235:genetics / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D054637:Dual-Specificity Phosphatases / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D020033:Protein Isoforms; D054637:Dual-Specificity Phosphatases; C483728:IBR5 protein, Arabidopsis