Novel receptor-like kinase ALE2 controls shoot development by specifying epidermis inArabidopsis

Abstract

The epidermis plays crucial roles in the development of various organs and in water retention in both animals and plants. In Arabidopsis thaliana, the subtilase ABNORMAL LEAF SHAPE 1 (ALE1) and the Arabidopsis homolog of the Crinkly4 (ACR4) receptorlike protein kinase (RLK) have been implicated in the intercellular communication that is required for surface functions of the epidermis. We have identified a novel mutant gene in Arabidopsis, ale2, which is associated with various epidermal defects, including disorganization of epidermis-related tissues, defects in the leaf cuticle and the fusion of organs. ALE2 encodes a previously uncharacterized RLK with a cluster of basic amino acid residues followed by a cysteine-containing sequence in the putative extracellular domain. Our genetic investigations suggest that ALE2 and ACR4 function in the same process, whereas ALE1 has a different mode of action, and that these three genes play partially overlapping roles in positively regulating protodermspecific gene expression and for the formation of leafy organs. We propose that at least two modes of intercellular communication facilitate the specification of epidermis, thereby promoting shoot organogenesis in Arabidopsis.

Arabidopsishomeodomain-leucine zipper IV proteins promote stomatal development and ectopically induce stomata beyond the epidermis

“…The HDG2 promoter also possesses L1 box (Nakamura et al, 2006), and its auto-activation may contribute to robust progression of stomatal development. Specification of the protoderm (L1 layer) in Arabidopsis involves cell-cell signaling mediated by receptor-like kinases ARABIDOPSIS CRINKLY4 (ACR4) and ABNORMAL LEAF SHAPE2 (ALE2), a putative cysteine peptidase DEFECTIVE KERNEL1 (AtDEK1) and a putative subtilase ALE1 (Becraft et al, 1996;Cao et al, 2005;Johnson et al, 2005;Tanaka et al, 2001;Tanaka et al, 2007). The signaling pathways appear to act upstream of AtML1 and PDF2, which in turn may promote expression of AtDEK1 and ALE2 as part of a positive-feedback loop (Javelle et al, 2011b).…”

The endosperm-specificZHOUPIgene ofArabidopsis thalianaregulates endosperm breakdown and embryonic epidermal development

“…The position of the T-DNA inserts was confirmed by PCR amplification and sequencing of genomic DNA flanking the inserts. The ale2-1 and ale1-1 mutations were provided by Hirokazu Tanaka (Tanaka et al, 2001;Tanaka et al, 2007). The acr4-2 mutation has been described previously (Gifford et al, 2003).…”

“…Mutations in either of two embryonically expressed genes encoding RLKs, ACR4 or ALE2, leads to a significant enhancement of the relatively mild ale1 phenotype. In double mutants, epidermal specification (as judged by the expression of the epidermal markers such as ATML1) is also partially lost (Tanaka et al, 2007;Watanabe et al, 2004). Neither acr4 nor ale2 mutants show a marked seedling phenotype, although both have cotyledon cuticle abnormalities, and the synergistic interactions of these genes may indicate that ACR4 and ALE2 are required to perceive a signal processed by ALE1.…”

Identification of genes specifically expressed in androgenesis-derived embryo in rapeseed (Brassica napus L.)

“…BnGemb-26 corresponded with an epidermis-specific gene FIDDLEHEAD (FDH), encoding a beta-ketoacyl-CoA synthase that mediates the addition of C2 unit to C16-C22 acyl-CoA to synthesize very long chain fatty acid (Yephremov et al 1999, Pruitt et al 2000. It is known that FDH is expressed in the protoderm in embryogenesis, ovule primodia and epidermis, and is essential for cuticle generation (Lolle et al 1992, Lolle and Cheung 1993, Tanaka et al 2007, and FDH is also expressed in the somatic embryo of white spruce (Stasolla et al 2003). Identification of such epidermis-specific genes suggests that epidermis differentiation is ongoing in globular embryos derived from micropores as well as zygotic embryogenesis.…”