Molecular mapping and characterization of BLMC, a locus for profuse wax (bloom) and enhanced cuticular features of Sorghum (Sorghum bicolor (L.) Moench.)

Authors: Burow, Gloria; Franks, Cleve; Xin, Zhanguo; Acosta-Martinez, Veronica

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2008
Publication Date: 1/1/2009
Citation: Burow, G.B., Franks, C.D., Xin, Z., Acosta Martinez, V. 2009. Molecular mapping and characterization of BLMC, a locus for profuse wax (bloom) and enhanced cuticular features of sorghum (Sorghum bicolor (L.) Moench.). Theoretical and Applied Genetics. 118:423-431.

Interpretive Summary: Among cereal crops, Sorghum (Sorghum bicolor Moench. L.) is considered one of the most drought tolerant and water efficient species. It is a highly valuable and sustainable crop that maintains commercial productivity under limiting water conditions. Sorghum has the C4 type of photosynthetic apparatus which serves as a mechanism in making the crop more physiologically efficient under high temperature and water deficit conditions. However, there exist prominent and distinctive morphological and physiological features that also contribute significantly to the overall drought tolerance of sorghum. One such feature is its low permeability cuticle with heavy deposit of visible bloom or epicuticular wax (EW) in the form of large wax flakes coupled with thick cuticle on the aerial organs of the plants. To date, there is no information available at the molecular level on bloom and cuticular function of sorghum. In this manuscript, we report the characterization and genetic mapping of a sorghum locus controlling cuticle with profuse bloom, BMC (Bloom-cuticle gene) using a mutant mapping population. Mutation in BMC locus (resulting in bloomless phenotype) reduced leaf and sheath wax load by 80-85%, and also leaf cuticle by 65-80 %. Bloomless bmc plants exhibit significant increase in cuticular permeability and plant death rating at anthesis. To map BMC, 100 F2 progenies from mutant mapping population were genotyped using microsattelite markers. BMC mapped to a 6cM interval in the terminal end of sorghum chromosome10 flanked by Xcup42 and Xsbarslbk7027. High resolution mapping showed that Xcup 49 and Xsbarslbk 7023 closedly delineate the locus to approximately 0.5cM interval. These findings demonstrate that sorghum has a unique cuticle-EW system which functions in a correlated manner. Genetic mapping of BMC will open avenues for dissection of genes in the cuticle- EW pathway and their application in enhancing abiotic stress tolerance in other crops.

Technical Abstract: Sorghum exhibits a distinct cuticle which produces profuse amount of epicuticular wax (EW) flakes (or bloom) on sheaths and leaves which is considered as a key morphological trait contributing to abiotic and biotic stress tolerance. However, information on the molecular nature of the trait is lacking. Here, we report the characterization and genetic mapping of a sorghum locus controlling cuticle with profuse bloom, BMC (Bloom-cuticle gene) using a mutant mapping population. Mutation in BMC locus (resulting in bloomless phenotype) reduced leaf and sheath wax load by 80-85%, and also leaf cuticle by 65-80 %. Bloomless bmc plants exhibit significant increase in cuticular permeability and plant death rating at anthesis. To map BMC, 100 F2 progenies from mutant mapping population were genotyped using microsattelite markers. BMC mapped to a 6cM interval in the terminal end of sorghum chromosome10 flanked by Xcup42 and Xsbarslbk7027. High resolution mapping showed that Xcup 49 and Xsbarslbk 7023 closedly delineate the locus to approximately 0.5cM interval. These findings demonstrate that sorghum has a unique cuticle-EW system which functions in a correlated manner. Genetic mapping of BMC will open avenues for dissection of genes in the cuticle- EW pathway and their application in enhancing abiotic stress tolerance in other crops.