Cassava starch is an important raw material for the production of food, starch-based chemical products, and bioethanol. Entering the 21st century, China's annual average imports of cassava raw materials reached 30 million tons of fresh cassava equivalent, and with the development of industry and product upgrading, the demand for waxy and high-amylose starch is becoming more and more urgent. Access to these new materials is no longer a dream, recently, SCCB team published a cover research paper in the Journal of Integrative Plant Biology to firstly report the production of cassava with high amylose content up to 50%.

Starch is a polysaccharide consisting of amylose and amylopectin to be accumulated in plant storage organs in the form of semicrystalline starch grains. Its composition affects the physicochemical properties and application potential of starch; therefore, genetic improvement of cassava starch quality has always been the goal of breeders. Previously, the team reported the creation of waxy cassava (Zhao et al. Biotechnology and Bioengineering, 2011) by interfering with the expression of the GBSSI gene, and obtained new cassava lines with low phosphorus content through the regulation of GWD1, a key gene for starch phosphorylation (Zhou et al., Scientific Reports, 2017). The team further found that cassava starch branch enzyme BE1 and BE2 showed very different temporal and spatial expression patterns and perform different functions: in the storage roots, BE1 expression was high in the daytime while BE2 in the night. When their expression interfered in cassava, both affect the normal growth of the plant, but only reduced BE2 expression caused the storage root rich in high amylose, as a result, leading to the changes in chain length distribution, paste characteristics of starch granules, and crystal characteristics. Reduced expression of BE1 in cassava can only have changed starch granule size. These results suggest that BE1 may regulate the accumulation of starch by interacting with other starch biosynthetic enzymes while BE2 is mainly involved in the amylopectin synthesis in cassava storage roots. The study also provides high-amylose cassava to support cassava industrialization.

The co-authors of the article “Production of very-high-amylose cassava by post-transcriptional silencing of branching enzyme genes” are Drs. Wenzhi Zhou and Shanshan Zhao. Prof. Peng Zhang is the corresponding author. The research was supported by several grants from the Chinese government.

References:

Zhou W#, Zhao S#, He S, Ma Q, Lu X, Hao X, Wang H, Yang J, Zhang P* (2019) Production of very-high-amylose cassava by post transcriptional silencing of branching enzyme genes. Journal of Integrative Plant Biology 62(6): 832-846.

Zhou W, He S, Naconsie M, Ma Q, Zeeman SC, Gruissem W, Zhang P (2017) Alpha-glucan, water dikinase 1 affects starch metabolism and storage root growth in cassava (Manihot esculenta Crantz). Scientific Reports 7: 9863.

Zhao SS, Dufour S, Sánchez T, Ceballos H, Zhang P (2011) Development of waxy cassava with different biological and physico-chemical characteristics of starches for industrial applications. Biotechnology and Bioengineering 108(8):1925-35.