| Sorghum (Sorghum bicolor L. Moench) is one of the earliest domesticated and most important cereal crops, with advantage of multipurpose, high stress tolerance and wide cultivation areas. Sorghum is a kind of energy and food crop with broad application prospects. Given the increasing global population, shrinking arable land area, and scarcity of water resources, people are expected to face serious global food shortage problems in the next 50 years. Therefore, breeding of high-yielding crop varieties, including sorghum, will have a profound impact on food security of the world. Currently, the use of conventional breeding methods to increase the yield of sorghum has become very limited, and the molecular breeding methods based on biological technology or genetic engineering will be able to effectively increase the yield of sorghum. Grain weight is an important component of grain yield, understanding the genetic basis of its regulation is the premise for molecular breeding of high-yielding sorghum. Therefore, QTL analysis for grain weight in sorghum and fine mapping of major QTL will have important theoretical significance and application value. Transgenic breeding is an effective method for molecular breeding and genetic transformation is an important method for functional verification of genes. Therefore, it is of great significance to establish a highly efficient genetic transformation protocol for sorghum using mature embryos as the explant materials.In the present study, using the populations derived from a cross between the grain sorghum variety SA2313 and the Sudan-grass variety Hiro-1, the QTL for grain weight were analyzed and two major QTL were fine mapped. Meanwhile, using the mature seeds of Hiro-1 as the explant materials, a high-efficiency genetic transformation system for sorghum was developed. The main results are as follows:1. Using an F2 population derived from a cross between SA2313 and Hiro-1, seven QTL for 100-grain weight were detected, which contributed between 7 and 40% of the phenotypic variation. According to the sorghum physical maps, all QTL detected are in the same regions with previously reported QTL for kernel weight.2. Two major QTL, qGW1 and qGW2, were detected consistently over 2 years and contributed 22%～40% and 13%～27% of the phenotypic variation, respectively in the F2 population of SA2313×Hiro-1.3. The QTL qGW1 was detected consistently across two other F2 populations, K-385×SA2313 and ATx623×SA2313. This illustrated that qGW1 was stable across multiple genetic backgrounds.4. Using extreme recombinants from a fine-mapping F3 population, we delimited qGW1 to a 101-kb region on the short arm of chromosome 1, containing 13 predicted gene models. According to the results of sequencing, we initially identified Sobic.001G038300 gene as the candidate gene of qGW1, which still need to be further verified.5. Near isogenic line of qGW1 was constructed, it will provide a powerful mapping population for further fine mapping of qGW1.6. A highly efficient genetic transformation protocol for sorghum was developed using mature embryos as the explant materials with an average transformation frequency of 12.31%, which provides an important basis for functional verification of important genes and molecular breeding of sorghum.Our data provide useful information for understanding the molecular basis of grain weight in sorghum. The SSR markers linked to the qGW1 locus can be used for improving sorghum grain yield through marker-assisted selection. Fine mapping of the qGW1 locus creates a basis for cloning this grain weight-related gene and understanding its regulation. |
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