The maize (Zea mays L.) roothairless3 gene encodes a putative GPI-anchored, monocot-specific, COBRA-like protein that significantly affects grain yield

Abstract

<p>The <em>rth3</em> (<em>roothairless 3</em>) mutant is specifically affected in root hair elongation. We report here the cloning of the <em>rth3</em> gene via a PCR-based strategy (amplification of insertion mutagenized sites) and demonstrate that it encodes a COBRA-like protein that displays all the structural features of a glycosylphosphatidylinositol anchor. Genes of the <em>COBRA</em> family are involved in various types of cell expansion and cell wall biosynthesis. The <em>rth3</em> gene belongs to a monocot-specific clade of the <em>COBRA</em> gene family comprising two maize and two rice genes. While the rice (<em>Oryza sativa</em>) gene <em>OsBC1L1</em> appears to be orthologous to <em>rth3</em> based on sequence similarity (86% identity at the protein level) and maize/rice synteny, the maize (<em>Zea mays</em> L.) <em>rth3-like</em> gene does not appear to be a functional homolog of <em>rth3</em>based on their distinct expression profiles. Massively parallel signature sequencing analysis detected <em>rth3</em> expression in all analyzed tissues, but at relatively low levels, with the most abundant expression in primary roots where the root hair phenotype is manifested.<em>In situ</em> hybridization experiments confine <em>rth3</em> expression to root hair-forming epidermal cells and lateral root primordia. Remarkably, in replicated field trials involving near-isogenic lines, the <em>rth3</em> mutant conferred significant losses in grain yield.</p>