Towards positional cloning and functional analysis of genes that control wax production in barley

University of Minnesota M.S. thesis.September 2018. Major: Applied Plant Sciences. Advisor: Gary Muehlbauer. 1 computer file (PDF); viii, 102 pages.Epicuticular waxes are the first point of contact between plants and their external environment, and provide mechanical and physiological support to plants. The leaf sheath and spike waxes of barley are rich in beta-diketone and hydroxy-beta-diketones that gives barley waxes a pronounced thread-like and fibrous morphology. Two previously described mutants are the subjects of this study namely: glossy sheath 2 (gsh2) and Glossy spike (Cer-yy). Both mutants exhibit a glossy (lack of epicuticular waxes) phenotype on the spike, while the gsh2 mutant also exhibits a glossy phenotype on the leaf sheaths on upper leaves. In this study, the gsh2 and Cer-yy mutants were exploited (1) to gain an increased understanding of the developmental timing and tissue specificity of wax accumulation; (2) to determine if gsh2 and/or Cer-yy mutants impact water retention; and (3) to fine map and identify candidate genes for GSH2 and CER-YY. Compared to wildtype, both mutants exhibited an absence of thread-like and fibrous waxes in the upper leaf sheaths and spikes, but an increased presence of plate-like lobed waxes following the elongation of the third internode. No significant differences in whole plant transpiration rates were observed between Bowman-gsh2, Bowman-Cer-yy and cv. Bowman in either high and low vapor pressure deficit conditions. Fine mapping populations segregating for GSH2 and CER-YY reduced the regions containing GSH2 to ~600Kbp and CER-YY to ~1.2 Mbp. Each region contains multiple candidate genes based on their functional annotation that warrant further research to isolate the respective causative genes