Phenotypical and gene co-expression network analyses of seed shattering in divergent sorghum (Sorghum spp.)

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.