Dissection of the Complex Phenotype in Cuticular Mutants of Arabidopsis Reveals a Role of SERRATE as a Mediator

Abstract

Mutations in LACERATA (LCR), FIDDLEHEAD (FDH), and BODYGUARD (BDG) cause a complex developmental syndrome that is consistent with an important role for these Arabidopsis genes in cuticle biogenesis. The genesis of their pleiotropic phenotypes is, however, poorly understood. We provide evidence that neither distorted depositions of cutin, nor deficiencies in the chemical composition of cuticular lipids, account for these features, instead suggesting that the mutants alleviate the functional disorder of the cuticle by reinforcing their defenses. To better understand how plants adapt to these mutations, we performed a genome-wide gene expression analysis. We found that apparent compensatory transcriptional responses in these mutants involve the induction of wax, cutin, cell wall, and defense genes. To gain greater insight into the mechanism by which cuticular mutations trigger this response in the plants, we performed an overlap meta-analysis, which is termed MASTA (MicroArray overlap Search Tool and Analysis), of differentially expressed genes. This suggested that different cell integrity pathways are recruited in cesA cellulose synthase and cuticular mutants. Using MASTA for an in silico suppressor/enhancer screen, we identified SERRATE (SE), which encodes a protein of RNA–processing multi-protein complexes, as a likely enhancer. In confirmation of this notion, the se lcr and se bdg double mutants eradicate severe leaf deformations as well as the organ fusions that are typical of lcr and bdg and other cuticular mutants. Also, lcr does not confer resistance to Botrytis cinerea in a se mutant background. We propose that there is a role for SERRATE-mediated RNA signaling in the cuticle integrity pathway.

Genome-Wide Analysis Uncovers Regulation of Long Intergenic Noncoding RNAs in Arabidopsis

“…The SEmediated splicing event is believed to prevent generation of related siRNAs to trigger posttranscriptional gene silencing . In addition, SE may also act as a transcription mediator (Voisin et al, 2009). By analysis of public tiling array data sets, we found that se-1, se-3, cbp20-1, and cbp80-285 indeed accumulated higher levels of pri-miRNAs compared with the wild type (see Supplemental Figure 14 online), confirming previous results (Laubinger et al, 2008).…”

The Formation and Function of Plant Cuticles

“…The fusion zones are often marked by two adjacent polysaccharide cell walls with no visible cuticle separating the two organs, although the fused epidermal layers maintain their identity, as indicated by the differentiation of internal nonfunctional stomata within fusion zones (Sieber et al, 2000). In each of three Arabidopsis mutants exhibiting organ fusions, lacerata, bodyguard, and fiddlehead, ectopic organ fusions and cuticular permeability defects could be partially suppressed by a second mutation in SERRATE (Voisin et al, 2009). SERRATE is a C 2 H 2 zinc finger protein that is required for microRNA biogenesis, and hypomorphic alleles exhibit numerous developmental defects, including serrated leaf margins (Dong et al, 2008).…”

Apoplastic Diffusion Barriers in Arabidopsis

“…In different accessions, the cuticle of the leaf blade is documented as a thin, electron-dense layer of 20-25 nm (Xiao et al, 2007;Voisin et al, 2009) (Figure 2A,D). A layered reticulate structure was observed at high magnification (Broun et al, 2004).…”

“…It has been speculated that these structures represent residual cutinization in the absence of a distinct cuticle layer on the surface of the cell wall (Bessire et al, 2007;Li et al, 2007b) (Figure 2B,2C). Arabidopsis mutants that exhibit alterations in the composition of cutin in the leaves, such as the lacerata (lcr) (At2g45970) and bodyguard (bdg) (At1g64670) mutants, typically display visible modifications to the ultrastructure of the leaf cuticle (Kurdyukov et al, 2006a;Voisin et al, 2009). In the aberrant induction of type three genes 1 (att1) (At4g00360) mutant, the cuticle is broader and more electron-translucent than that of wt Arabidopsis (Xiao et al, 2004) (Figure 2E), while WAX INDUCER1/ SHINE1 (win1/shn1) (At1g15360)-overexpressing plants accumulate electron-dense material beneath a broad electron-translucent cuticle proper (Broun et al, 2004).…”