On August 17, 2022, our team published an article in the Journal of Molecular Sciences entitled "Knockdown of p-Coumaroyl Shikimate/Quinate 3′-Hydroxylase Delays the Occurrence of Post-Harvest Physiological Deterioration in Cassava Storage Roots". The study reported the expressional repression of coumarate 3-hydroxylase gene (C3'H) results in the delayed occurrence of post-harvest physiological deterioration in cassava storage roots, confirming that C3'H is the key gene involved in coumarin synthesis and plays an important role in the phenotypic occurrence of PPD.

Cassava is rich in starch in storage roots, high yielding, and tolerant to drought and infertile soils. As a key component of food security and bioenergy development, is a pioneer crop for the major strategic deployment of the double carbon target. However, After harvest, cassava storage roots undergo browning or bluish browning discoloration, the so-called post-harvest physiologic deterioration (PPD). The occurrence of PPD involves a series of physiological and biochemical events such as gene expression, reactive oxygen species (ROS) scavenging, secondary metabolite synthesis, and signal transduction. Previous studies have shown that by synergistic expression of superoxide dismutase (MeCu/ZnSOD) and catalase (MeCAT1), cassava ROS scavenging ability can be enhanced to delay PPD occurs for up to 10 days (Xu et al., 2013), and melatonin is found to regulate the ROS clearance system to affect the process of PPD (Ma et al., 2016). The vascular bundle-specific expression of lysozyme inhibited the activity of polyphenol oxidase, reduced the degree of postharvest browning of cassava, and delayed the occurrence of PPD symptoms (Wu et al., 2022).

To further verify that coumarin synthesis is a major factor in the occurrence of PPD symptoms, our team generated transgenic cassava with repressed expression of p-coumaroyl shikimate/quinate 3′-hydroxylase by RNAi approach. The field growth phenotype of the transgenic plants was normal and the occurrence of PPD in the storage roots was significantly slower than that of the wild type. The content of scopoletin and scopolin, together with lignin, was also significantly reduced than that of the wild type. The study shows that C3'H is a key enzyme for the synthesis of secondary metabolites of coumarins, which is involved in the occurrence of PPD symptoms of cassava storage roots, and provides a target gene for subsequent gene editing to breed PPD-tolerant cassava germplasm.

The research was funded by the National Key Research and Development Program and the China Agriculture Research System.

Article link: https://www.mdpi.com/1422-0067/23/16/9231