MYB and HD-ZIP IV homologs related to trichome formation are involved in epidermal bladder cell development in the halophyte <i>Mesembryanthemum crystallinum</i> L.

<p>The common ice plant, <i>Mesembryanthemum crystallinum L</i>., a halophytic new functional leafy vegetable crop, develops epidermal bladder cells (EBCs) on the surfaces of its aerial organs. Our previous studies of the physiological characteristics of the wild-type and the EBC-less mutant indicated that EBCs sequester salt and maintain ion homeostasis within photosynthetically active tissues. The EBC has been thought to be a modified trichome; however, molecular mechanisms governing EBC development in the common ice plant have not been fully understood. Here, we have analyzed the steady-state mRNA abundance of nineteen cotton fiber-related gene homologs and eight <i>Arabidopsis</i> trichome development-related genes, and found that a MYB transcription factor homolog (<i>McMYB2</i>) and a <i>GLABRA2</i>-like gene (<i>McC4HDZ</i>) were preferentially expressed in wild-type plants, whereas a putative <i>TRIPTYCHON</i> (<i>McTRY</i>)- and <i>CAPRICE</i>-like gene (<i>McCPC</i>) were preferentially expressed in the EBC-mutant. The full-length cDNA sequences of these homologs were determined, and constructs containing <i>McC4HDZ</i> and <i>McMYB2</i> were introduced into an <i>Arabidopsis</i> trichome-less mutant and wild-type plants. Overexpression of <i>McMYB2</i> in wild-type <i>Arabidopsis</i> increased trichome number, associated with activation of the trichome development-related gene, <i>GLABRA2</i> (<i>GL2</i>). Moreover, overexpression of <i>McC4HDZ</i> partially complemented trichome development in the trichome-less mutant of <i>gl2</i>-<i>1</i>, and resulted in increased trichome number in wild-type <i>Arabidopsis</i>, associated with the upregulation of key trichome-positive regulators <i>GLABRA1</i> (<i>GL1</i>) and <i>TRANSPARENT TESTA GLABRA1</i> (<i>TTG1</i>). These results suggest that <i>McMYB2</i> and <i>McC4HDZ</i> could be functional in <i>Arabidopsis</i> trichome formation, implying that EBCs of the common ice plant and trichomes of <i>Arabidopsis</i> may share some molecular mechanisms in their development.</p>