Positional Cloning and Functional Analysis of Genes That Control Wax Production in Barley

Epicuticular waxes provide a primary water resistant barrier and protection against different environmental stresses like pests, radiation and disease pathogens. Association mapping in a barley advanced backcross NAM population identified QTL on chromosome 3HL and 1HS that were associated with glossy phenotypes. The QTL on chromosome 3HL and 1HS are coincident with a recessive mutant, glossy sheath 2 (gsh2), and a dominant mutant, Eceriferum-yy (Cer-yy), respectively. The objectives of this project were to characterize the phenotypes of both mutants and to isolate GSH2. Scanning electron microscopy (SEM) confirmed the dramatic reduction of wax on the flag leaf sheath on gsh2 mutants and the lemma and palea of Cer-yy mutants. To examine the transition of wax accumulation between the two mutants and wildtype, a developmental analysis was conducted. F₂ mapping populations segregating for the gsh2 mutant were developed and GSH2 was fine mapped. Over 1800 F₂ individuals were genotyped with markers that flank the GSH2 locus and 85 recombinants were identified reducing the interval to a <1 cM region. Candidate genes have been identified and resequencing gsh2 alleles is in progress. Preliminary data from vapor pressure deficit experiments, indicated higher transpiration rates for the ­­Bowman-Cer-yy and Bowman-gsh2 mutants than Bowman. To measure non-stomatal transpiration rates in the mutants during induced water deficit conditions, drought response experiments will be conducted.