Sorghum is the fifth largest grain crop in the world and can be used for food, feed, brewing and bioenergy. Sorghum genetic transformation technology is an essential and important tool in the research of sorghum functional genomics and can also serve as an important complement to traditional breeding methods. In this review, we summarize the research progress of sorghum transformation in recent years, analyze the problems in sorghum genetic transformation and propose strategic solutions to them in order to provide a reference for further improvement of sorghum genetic transformation technology. By summarizing more than 50 literatures on sorghum tissue culture and genetic transformation in recent years, we introduced the current research status of sorghum genotypes, explant sources, and regeneration system construction for genetic transformation, and compared the advantages and disadvantages of four commonly used methods for sorghum genetic transformation: electroporation, pollen-mediated transformation, particle bombardment and Agrobacterium-mediated transformation, summarized the effects of the main components of genetic transformation vectors, including promoters, target genes, selective marker genes and reporter genes, on transformation efficiency, explained the current application status of sorghum genetic transformation, analyzed the main bottleneck problemns in sorghum genetic transformation technology, and studied countermeasures. Sorghum genotypes have a significant influence on tissue culture and P898012 and Tx430 are the most widely used. Gene bombardment and Agrobacterium-mediated transformation are the most commonly used methods for sorghum genetic transformation, and the advantages of Agrobacterium-mediated transformation are gradually emerging. In vector construction, CaMV35S and ubi1 are the most commonly used promoters, and antibiotic resistance genes (nptII, hpt), herbicide resistance genes (bar), and nutrient assimilation genes are the three commonly used selection markers. With the development of sorghum genetic transformation technology and CRISPR/Cas9-mediated gene editing technology, some genes with important agronomic traits have been successfully transferred into sorghum. However, strong genotype dependence, long tissue culture cycle, and poor genetic transformation stability are the main bottlenecks that limit the genetic transformation of sorghum. By introducing morphogenesis regulatory factors, somatic cell generation can be directly performed, which shortens the tissue culture cycle, improves the transformation efficiency, and expands the source of explants. This has become a major breakthrough in sorghum genetic transformation technology. The use of morphogenesis regulatory factors and adoption of cut-dip-budding (CDB) delivery system can further improve the sorghum genetic transformation technology. Combined with the application of CRISPR/Cas9 gene editing technology, they will surely provide an important technical basis for the sorghum molecular breeding and gene function identification.

Sorghum [Sorghum bicolor (L.) Moench], a multipurpose C₄ crop, is also a model species of the Poaceae family for plant research. During the process of domestication, the modification of seed dispersal mode is considered a key event, as the loss of seed shattering caused a significant increase in yield. In order to understand the seed shattering process in sorghum, we further studied eight previously identified divergent sorghum germplasm with different shattering degrees. We described their phenotypes in great detail, analyzed the histology of abscission zone, and conducted a gene co-expression analysis. We observed that the abscission layer of the most strong-shattering varieties began to differentiate before the 5–10 cm panicles development stage and was completely formed at flag leaf unfolding. The protective cells on the pedicels were also fully lignified by flowering. Through the weighted gene correlation network analysis (WGCNA), we mined for candidate genes involved in the abscission process at the heading stage. We found that these genes were mainly associated with such biological processes as hormone signal transmission (SORBI_3003G361300, SORBI_3006G216500, SORBI_3009G027800, SORBI_3007G077200), cell wall modification and degradation (SORBI_3002G205500, SORBI_3004G013800, SORBI_3010G022400, SORBI_3003G251800, SORBI_3003G254700, SORBI_3003G410800, SORBI_3009G162700, SORBI_3001G406700, SORBI_3004G042700, SORBI_3004G244600, SORBI_3001G099100), and lignin synthesis (SORBI_3004G220700, SORBI_3004G062500, SORBI_3010G214900, SORBI_3009G181800). Our study has provided candidate genes required for shedding for further study. We believe that function characterization of these genes may provide insight into our understanding of seed shattering process.