Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2017
Publication Date: 1/12/2018
Citation: Jiao, Y., Burow, G.B., Gladman, N., Acosta Martinez, V., Chen, J., Burke, J.J., Ware, D., Xin, Z. 2018. Efficient identification of causal mutations through sequencing of bulked F2 from two allelic bloomless mutants. Frontiers in Plant Science. doi.org/10.3389/fpls.2017.02267.
Interpretive Summary: dentification of causal mutations underlying a mutant phenotype, the forward genetic method, is a powerful approach to elucidate gene function. Conventional forward genetic method, the map-based cloning, takes 3 to 5 years' meticulous research effort to identify a causal mutation. Through collaboration with Cold Spring Harbor laboratory, scientists from USDA-ARS at Lubbock, Texas developed a pipeline to identify causal mutations by sequencing the bulked F2s of two allelic bloomless mutants. The pipeline needs only one week of bioinformatic work to identify the causal gene. This method greatly increased the efficiency of gene discovery in sorghum and can be applied to other crops.
Technical Abstract: Sorghum (Sorghum bicolor Moench, L.) plant accumulates copious layers of epi-cuticular waxes (EW) on its aerial surfaces, more spectacular than most other crops. It provides a vapor barrier to reduce water loss and is considered as a major determinant of its superior drought tolerance. However, little is known about the genes responsible for wax accumulation in sorghum. We isolated two allelic mutants completely devoid of EW layer, named bloomless40-1 (bm40-1) and bm40-2, from two independent mutant lines. Each bm mutant was crossed to BTx623, the parent for the sorghum pedigreed mutant library, to generated F2 populations segregating for the bm phenotype. Genomic DNA from 20 bm F2 plants from each population were bulked for whole genome sequencing. Only one gene encoding a GDSL-like lipase/acylhydrolase was found to have unique homozygous mutations in each bulked F2 population. The mutant bm40-1 harbored a missense mutation in the gene, and in bm40-2 had a splice donor site mutation. Thus, we provided strong evidence that this GDSL-like lipase gene is the causal gene for the bm phenotype. Our result demonstrated that allelic MutMap was an efficient method to identify causal mutations and provided an opportunity to gain understanding how sorghum plant accumulate such abundant EW on its aerial surface and tools to engineer drought tolerant crops with reduced water loss.