A role for <it>BELLRINGER</it> in cell wall development is supported by loss-of-function phenotypes

• Main Authors: Etchells J, Moore Lucy, Jiang Wen, Prescott Helen, Capper Richard, Saunders Nigel J, Bhatt Anuj M, Dickinson Hugh G
• Format: Article
• Language: English
• Published: BMC 2012-11-01
• Series: BMC Plant Biology
• Online Access: http://www.biomedcentral.com/1471-2229/12/212

<p>Abstract</p> <p>Background</p> <p>Homeodomain transcription factors play critical roles in metazoan development. <it>BELLRINGER</it> (<it>BLR</it>), one such transcription factor, is involved in diverse developmental processes in <it>Arabidopsis</it>, acting in vascular differentiation, phyllotaxy, flower and fruit development. <it>BLR</it> also has a redundant role in meristem maintenance. Cell wall remodelling underpins many of these processes, and <it>BLR</it> has recently been shown to regulate expression of <it>PECTIN METHYL-ESTERASE 5 (PME5)</it>, a cell wall modifying enzyme in control of phyllotaxy. We have further explored the role of <it>BLR</it> in plant development by analysing phenotypes and gene expression in a series of plants over-expressing <it>BLR</it>, and generating combinatorial mutants with <it>blr</it>, <it>brevipedicellus</it> (<it>bp),</it> a member of the <it>KNOX1</it> family of transcription factors that has previously been shown to interact with <it>blr</it>, and the homeodomain transcription factor <it>revoluta</it> (<it>rev</it>), required for radial patterning of the stem.</p> <p>Results</p> <p>Plants over-expressing BLR exhibited a wide range of phenotypes. Some were defective in cell size and demonstrated misregulation of genes predominantly affecting cell wall development. Other lines with more extreme phenotypes failed to generate lateral organs, consistent with BLR repressing transcription in the shoot apex. Cell wall dynamics are also affected in <it>blr</it> mutant plants, and <it>BLR</it> has previously been shown to regulate vascular development in conjunction with <it>BP</it>. We found that when <it>bp</it> and <it>blr</it> were combined with <it>rev</it>, a set of defects was observed that were distinct from those of <it>bp blr</it> lines. In these triple mutants xylem development was most strikingly affected, resulting in an almost complete lack of vessels and xylem parenchyma with secondary thickening.</p> <p>Conclusions</p> <p>Our data support a role for <it>BLR</it> in ordering the shoot apex and, in conjunction with <it>BP</it> and <it>REV,</it> playing a part in determining the composition and organisation of the vascular system. Microarray analysis strongly indicates that the striking vascular phenotypes of <it>blr bp rev</it> triple mutants and plants over-expressing <it>BLR</it> result from the misregulation of a suite of genes, targets of BLR in wild type plants, that determine cell size and structure in the developing vasculature.</p>