Dissertation/Thesis Abstract

The evolution of <i>BARREN INFLORESCENCE1</i> and related AUX/IAA genes in angiosperms
by Child, Robert Joseph, M.S., California State University, Long Beach, 2013, 82; 1527538
Abstract (Summary)

The plant hormone auxin plays a major role in shaping plant morphology and development, but the gene networks regulating its synthesis and transport are incompletely known. The maize BARREN INFLORESCENCE 1 (BIF1) gene has recently been cloned and shown to play an important role in the early stages of polar auxin transport. Auxin is synthesized in shoot tips and transported basipetally through the plant shoot and acts as a morphogen by facilitating the degradation of transcriptional repressors in a concentration dependent manner. The AUX/IAA gene family encodes transcriptional repressors that regulate a subset of plant developmental responses governed by the transcription of early auxin inducible genes in plants. Although the maize BIF1 gene is a member of the AUX/IAA gene family, the co-ortholog(s) of BIF1 in Arabidopsis thaliana was not known prior to this research.

Bayesian phylogenetic reconstruction placed maize BIF1 in a clade sister to Arabidopsis thaliana AtIAA15. The BIF1 lineage has undergone two gene duplications since the divergence of the early grasses. Molecular evolutionary analyses by maximum likelihood suggest that the BIF1 alignment is under strong purifying selection with positive selection acting on a glutamine residue located in a functional region associated with AUX/IAA protein dimerization in one clade of BIF1 paralogs, the BIF1-Like2 (BIF1L2) clade. A character reconstruction analysis using maximum parsimony estimated an adenine to cytosine transversion at the base of the BIF1L2 clade changed a glutamine into an alanine residue in this functional region. Expression of BIF1 orthologs is conserved in floral meristems in the eudicot AtIAA15 clade containing the taxa Erianthe Guttata, Arabidopsis thaliana, Medicago truncatula, however grass BIF1L2 expression has diverged within the PACMAD – BEP clade, specifically in rice, where BIF1L2 expression is reported to have moved into root tissue. These results suggest that BIF1 paralogs has changed following a second round of gene duplication in the grasses. Taken together, a change in localized expression in these sequences, and positive selection acting on a glutamine-rich region of the protein-protein binding motif could imply that BARREN INFLORESCENCE1-like2 proteins are probably interacting with a new set or subset of AUXIN RESPONSE FACTOR (ARF) binding partners, and that neofunctionalization has occurred in the BARREN INFLORESCENCE1-like2 clade.

Indexing (document details)
Advisor: Malcomber, Simon
Commitee: Brusslan, Judith, Carter, Ashley
School: California State University, Long Beach
Department: Biological Sciences
School Location: United States -- California
Source: MAI 52/05M(E), Masters Abstracts International
Source Type: DISSERTATION
Subjects: Plant biology, Evolution and Development, Plant sciences
Keywords: Barren inflorescence, Inflorescence morphology, Plant phylogenetics, Polar auxin transport
Publication Number: 1527538
ISBN: 9781303795770
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