PhD Candidate Monash University Clayton, Victoria, Australia
Body of Abstract: Cyanogenic glucosides are well-known for their role in defence, releasing toxic hydrogen cyanide upon tissue disruption. However, as nitrogen-containing compounds, they can be costly to produce. Recent research has suggested that cyanogenic glucosides may have multifunctional roles beyond defence. Sorghum bicolor, a widely produced grain and forage crop, contains high amounts of the cyanogenic glucoside dhurrin and also accumulates nitrate, which can be toxic at high levels.
In this study, we investigated the metabolism of dhurrin in Sorghum under nitrogen starvation and re-supply conditions. Plants were grown under nitrogen-limiting conditions until they reached maturity and were then treated with a high nitrogen surge or a control solution. We collected samples from leaf, stem, and roots for analysis of dhurrin and nitrate content, and gene expression using RNAseq. Our results showed that significant increases in nitrate content were observed in root and sheath tissue from as early as 12-hours post surge, but no increase was detected in leaf nitrate over the sampling period in treated plants. Differences in dhurrin content were not detected until 24-hours post treatment, and only in leaf and sheath tissues. We also found that the dhurrin biosynthesis genes CYP79A1 and CYP71E1 were upregulated in treated plants in leaf 24-hours after the surge in comparison to control plants, while genes involved in dhurrin recycling were downregulated in stem tissue at 24-hours post-surge.
Our findings support the role of dhurrin as a nitrogen-storage compound, suggesting that its levels in the plant are dependent on the interplay of both synthesis and turnover rates. The data produced in this study could also contribute to the identification of regulatory genes controlling the pathway. Overall, this research sheds new light on the multifunctionality of cyanogenic glucosides and provides insights into the mechanisms underlying their role in plant growth and adaptation to nitrogen limitation.