MYB and HD-ZIP IV homologs related to trichome formation are involved in epidermal bladder cell development in the halophyteMesembryanthemum crystallinumL.

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 trichomeless 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.Abbreviations: AGPC, acid guanidinium thiocyanate phenol chloroform; EBC, epidermal bladder cell; CAM, crassulacean acid metabolism; CaMV35S, cauliflower mosaic virus; CTAB, hecadecyltrimethylammonium bromide; RT-PCR, reverse transcription-PCR

Adaptive Mechanisms of Halophytes and Their Potential in Improving Salinity Tolerance in Plants

“…A positive correlation between the presence and/or the number of EBCs and salt tolerance was reported in Chenopodium quinoa [ 74 , 78 ]. Some candidate genes related to EBC formation were recently identified using transcriptome analysis in C. quinoa , Mesembryanthemum crystallinum, and Atriplex centralasiatica species [ 79 , 80 , 81 ] ( Table 1 ). More fundamentally, Imamura et al [ 82 ] first identified a gene, named reduced epidermal bladder cells ( REBC ), involved in the EBC development in C. quinoa , laying the foundation for elucidating the EBC-associated stress tolerance mechanism in halophytes.…”

A novel WD40-repeat protein involved in formation of epidermal bladder cells in the halophyte quinoa

“…Furthermore, 57 of 92 genes upregulated by at least 2-fold in the mutant were also expressed in EBCs (Supplementary Data 4). Next, we compared the genes with altered expression in rebc mutants were compared with those whose expression was altered in a mutant form of M. crystallinum that lacked EBCs 13,14 . A gene belonging to the jasmonate-induced protein family was downregulated in both M. crystallinum (WM28; NCBI Acc.…”

“…Although physiological analysis has elucidated some aspects of EBC function 9,10 , no studies to date have investigated how EBCs develop. Recently, some candidate genes related to EBC formation were selected in M. crystallinum 13,14 . However, because the key genes involved in EBC formation have not yet been isolated, the molecular mechanism underlying the formation of these important cells remains unknown.…”

The role of HD‐Zip class I transcription factors in plant response to abiotic stresses

“…Soil salinization is an increasingly significant factor affecting plant growth and crop productivity. It is reported that salinity decreases the average yields of major crops by more than 50% (Bray et al , Roeurn et al ). Numerous mechanisms that regulate the transcription of HD‐Zip I genes involved in response to salt stress have been studied (Shen et al 2003, Ariel et al , Li et al , , Bhattacharjee et al , Wu et al , Zhang et al ).…”