Project description:Phytomonas are a large and diverse sub-group of plant-infecting trypanosomatids that are relatively poorly understood. Little is known of their biology or how they have adapted to life inside plants. This study sequenced the genome of the Cassava (Manihot esculenta) infecting species Phytomonas francai to provide additional genome resources and new insight into the biology of this poorly understood group of organisms.
Project description:Cassava (Manihot esculenta) is one of the most important staple food crops worldwide. Its starchy tuberous roots supply over 800 million people with carbohydrates. Yet, surprisingly little is known about the processes involved in filling of those vital storage organs. A better understanding of cassava carbohydrate allocation and starch storage is key to improve storage root yield. In this work, we studied cassava morphology and phloem sap flow from source to sink using transgenic pAtSUC2::GFP plants, the phloem tracers esculin and 5(6)-carboxyfluorescein diacetate (CFDA), as well as several staining techniques. We show that cassava performs apoplasmic phloem loading in source leaves and symplasmic unloading into phloem parenchyma cells of tuberous roots. We demonstrate that vascular rays play an important role in radial transport from the phloem to xylem parenchyma cells in tuberous roots. Furthermore, enzymatic and proteomic measurements of storage root tissues confirmed high abundance and activity of enzymes involved in the sucrose synthase-mediated pathway and indicated that starch is stored most efficiently in the outer xylem layers of tuberous roots. Our findings represent a first basis for biotechnological approaches aimed at improved phloem loading and enhanced carbohydrate allocation and storage in order to increase tuberous root yield of cassava.
Project description:<p>Cassava (Manihot esculenta Crantz) storage roots exhibit significant variation in starch content among cultivars, yet the metabolic and molecular mechanisms governing carbon allocation between storage and structural components remain poorly understood. Here, we investigated carbon partitioning in two cassava cultivars with distinct starch phenotypes: high-starch FX01 and low-starch SC16. Using 13C isotope labeling coupled with metabolomic analysis, we traced the pathway of carbohydrates through primary and secondary metabolism. The results revealed that SC16 exhibits enhanced photosynthetic capacity and elevated soluble sugar content in storage roots, whereas FX01 demonstrates superior starch synthesis due to its efficient glucose and fructose phosphorylation. Conversely, SC16 exhibits a faster conversion of 13C-labeled ferulic acid, directing carbon flow towards lignin biosynthesis via the phenylpropanoid pathway. Further, by silencing the MeCOMT8 gene, encoding a key enzyme in ferulic acid biosynthesis, we observed a reduction in lignin content and an increase in ADP-glucose levels in the MeCOMT8-silenced cassava plants, suggesting a regulatory link between these competing pathways. Our research elucidated that the variations in carbon allocation between starch and lignin biosynthesis among different cultivars are finely orchestrated though the specific-step alteration of metabolic flux. These findings provide potential candidate targeted points and valuable insights for high-starch breeding in cassava.</p>
