Abstract
The common ice plant, Mesembryanthemum crystallinum L., 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 Arabidopsis trichome development-related genes, and found that a MYB transcription factor homolog (McMYB2) and a GLABRA2-like gene (McC4HDZ) were preferentially expressed in wild-type plants, whereas a putative TRIPTYCHON (McTRY)- and CAPRICE-like gene (McCPC) were preferentially expressed in the EBC-mutant. The full-length cDNA sequences of these homologs were determined, and constructs containing McC4HDZ and McMYB2 were introduced into an Arabidopsis trichome-less mutant and wild-type plants. Overexpression of McMYB2 in wild-type Arabidopsis increased trichome number, associated with activation of the trichome development-related gene, GLABRA2 (GL2). Moreover, overexpression of McC4HDZ partially complemented trichome development in the trichome-less mutant of gl2-1, and resulted in increased trichome number in wild-type Arabidopsis, associated with the upregulation of key trichome-positive regulators GLABRA1 (GL1) and TRANSPARENT TESTA GLABRA1 (TTG1). These results suggest that McMYB2 and McC4HDZ could be functional in Arabidopsis trichome formation, implying that EBCs of the common ice plant and trichomes of Arabidopsis may share some molecular mechanisms in their development.
Highlights
Soil salinization is an increasingly important factor limiting plant growth and crop productivity
Several recent studies showed the contributions of epidermal bladder cell (EBC) to the adaptation of the common ice plant to salt stress including a mutational study on the role of EBCs in the salinity tolerance (Agarie et al, 2007), a proteomic analysis to identify the proteins expressed in response to salt stress (Cosentino et al, 2013), and a transcriptome analysis to detect the cell-type specific responses to salinity (Oh et al, 2015)
We isolated WM28, a putative jasmonate-induced gene, an EBC developmentrelated gene using a cDNA based-suppression subtractive hybridization (SSH) and we showed that WM28 positively regulated trichome in Arabidopsis by increase of the expression of genes for trichome development-acting complex, GL1 and GL3 (Roeurn et al, 2016)
Summary
Soil salinization is an increasingly important factor limiting plant growth and crop productivity. Estimates indicate that salinity decreases the average yields of major crops by more than 50% (Bray et al, 2000). Halophytes naturally inhabit saline environments and tolerate salt concentrations of 200 mM or more at which approximately 99% of other plant species would die (Flowers & Colmer, 2008; Shabala, 2013). Halophytes have developed numerous strategies to adapt to high salinity. These adaptive mechanisms include osmotic adjustment through compartmentation of ions into vacuoles, accumulation of compatible solutes, succulence, and secretion of salt into specialized epidermal cells
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