Regulation of dhurrin pathway gene expression during Sorghum bicolor development

Abstract

Main conclusion Developmental and organ-specific expression of genes in dhurrin biosynthesis, bio-activation, and recycling offers dynamic metabolic responses optimizing growth and defence responses in Sorghum. Abstract Plant defence models evaluate the costs and benefits of resource investments at different stages in the life cycle. Poor understanding of the molecular regulation of defence deployment and remobilization hampers accuracy of the predictions. Cyanogenic glucosides, such as dhurrin are phytoanticipins that release hydrogen cyanide upon bio-activation. In this study, RNA-seq was used to investigate the expression of genes involved in the biosynthesis, bio-activation and recycling of dhurrin in Sorghum bicolor. Genes involved in dhurrin biosynthesis were highly expressed in all young developing vegetative tissues (leaves, leaf sheath, roots, stems), tiller buds and imbibing seeds and showed gene specific peaks of expression in leaves during diel cycles. Genes involved in dhurrin bio-activation were expressed early in organ development with organ-specific expression patterns. Genes involved in recycling were expressed at similar levels in the different organ during development, although post-floral initiation when nutrients are remobilized for grain filling, expression of GSTL1 decreased > tenfold in leaves and NITB2 increased > tenfold in stems. Results are consistent with the establishment of a pre-emptive defence in young tissues and regulated recycling related to organ senescence and increased demand for nitrogen during grain filling. This detailed characterization of the transcriptional regulation of dhurrin biosynthesis, bioactivation and remobilization genes during organ and plant development will aid elucidation of gene regulatory networks and signalling pathways that modulate gene expression and dhurrin levels. In-depth knowledge of dhurrin metabolism could improve the yield, nitrogen use efficiency and stress resilience of Sorghum.

Cyanogenesis in the Sorghum Genus: From Genotype to Phenotype

“…Unless cyanogenesis is specifically induced by insect or pest attacks, this suggests that the wild, undomesticated Sorghum species do not utilize cyanogenic glucosides as part of their chemical defense, particularly as leaves are considered the plant organ most vulnerable to predation. Production of dhurrin in S. bicolor is developmentally regulated, with concentrations often found to be highest in young, developing tissues, such as newly formed leaves [ 52 , 65 , 66 , 67 , 68 , 69 ]. In terms of cyanogenesis, this pattern is consistent with the optimal resource allocation theory, in that leaves are generally the most heavily defended organ as they house the photosynthetic apparatus [ 70 , 71 ].…”

Wounding and methyl jasmonate increase cyanogenic glucoside concentrations in Sorghum bicolor via upregulation of biosynthesis

“…2018; Gleadow et al . 2021). Kiani & Szczepaniec (2018) similarly observed a relatively low expression of SbCYP79A1 and SbUGT85B1 in their studies of defence pathways in sorghum.…”

Comparative analysis of sorghum (C4) and rice (C3) plant headspace volatiles induced by artificial herbivory

“… 50 Finally, volatiles in sorghum could be functionally tuned down for a lower activity, possibly due to “redundancy” in defense implied from the evolution and use of the potent cyanogenic glycoside dhurrin in sorghum species. 51 …”