Mucilage secretion by aerial roots in sorghum (Sorghum bicolor): sugar profile, genetic diversity, GWAS and transcriptomic analysis

Key messageSorghum accessions showed considerable genotypic variation in mucilage secretion. Both GWAS and transcriptome analyses suggested the involvement of a UDP-glycosyltransferase gene (Sobic.010G120200) and the glucuronidation pathway in mucilage secretion in sorghum. Aerial root mucilage can enhance nitrogen fixation by providing sugar and low oxygen environment to the rhizosphere microbiome in Sierra Mixe maize. Aerial root mucilage has long been documented in sorghum (Sorghum bicolor), but little is known about the biological significance, genotypic variation, and genetic regulation of this biological process. In the present study, we found that a large variation of mucilage secretion capacity existed in a sorghum panel consisting of 146 accessions. Mucilage secretion occurred primarily in young aerial roots under adequately humid conditions but decreased or stopped in mature long aerial roots or under dry conditions. The main components of the mucilage-soluble were glucose and fructose, as revealed by sugar profiling of cultivated and wild sorghum. The mucilage secretion capacity of landrace grain sorghum was significantly higher than that of wild sorghum. Transcriptome analysis revealed that 1844 genes were upregulated and 2617 genes were downregulated in mucilage secreting roots. Amongst these 4461 differentially expressed genes, 82 genes belonged to glycosyltransferases and glucuronidation pathways. Sobic.010G120200, encoding a UDP-glycosyltransferase, was identified by both GWAS and transcriptome analysis as a candidate gene, which may be involved in the regulation of mucilage secretion in sorghum through a negative regulatory mechanism.

Automated summary

Sorghum accessions showed significant genotypic variation in mucilage secretion. The involvement of a UDP-glycosyltransferase gene (Sobic.010G120200) and the glucuronidation pathway in mucilage secretion in sorghum was suggested by GWAS and transcriptome analyses. Aerial root mucilage in Sierra Mixe maize can enhance nitrogen fixation by providing sugar and low oxygen environment to the rhizosphere microbiome. However, the biological significance, genotypic variation, and genetic regulation of aerial root mucilage in sorghum are poorly understood. This study found a large variation in mucilage secretion capacity among 146 sorghum accessions, with secretion occurring primarily in young aerial roots under humid conditions and decreasing or stopping in mature long aerial roots or dry conditions. The main components of the mucilage were glucose and fructose, and landrace grain sorghum had higher mucilage secretion capacity than wild sorghum. Transcriptome analysis identified 4461 differentially expressed genes, including 82 genes belonging to glycosyltransferases and glucuronidation pathways. Sobic.010G120200, encoding a UDP-glycosyltransferase, was identified as a candidate gene involved in the regulation of mucilage secretion in sorghum.