Identification of Cer-Zv, a Gene Responsible for Cutin Formation in the Barley Leaf Cuticle

The recessive mutation cer-zv induces drought hypersensitivity in barley. Its presence is associated with a decreased deposition of cutin and a significant reduction in the thickness of the leaf cuticle. The mutation was initially mapped to a 1.7 cM interval in the pericentromeric region of chromosome 4H, a location which was later narrowed, using a fine mapping procedure with a progeny equivalent to 7490 gametes, to a 0.02 cM interval on the short arm. Although genetically small, this interval still represents more than half of the chromosome arm, as shown by an analysis of a set of markers positioned in a barley cytological map based on chromosome dissection lines. As a result, a map-based cloning approach to isolate the gene is unlikely to be feasible. As an alternative, we have compared the RNA-seq based transcriptome of the mutant with its wild type, and have been able to identify 16 genes located in the expected genomic region which feature mis-sense mutations (SNPs or indels). Two of these genes are likely to be functionally related with cutin formation, so these were targeted for re-sequencing among wild type lines and eight carriers of cer-zv. The procedure has led to the identification of cer-zv, which encodes a member of the Gly-Asp-Ser-Leu (GDSL) esterase/lipase family of plant proteins possibly involved in the polymerization of cutin monomers. The gene is heavily transcribed in the leaf elongation zone where cutin deposition occurs most strongly. The indication is that cer-zv is involved in the formation of cutin in the barley leaf cuticle.