Overexpression of the bamboo sucrose synthase gene (BeSUS5) improves cellulose production, cell wall thickness and fiber quality in transgenic poplar

Abstract

In plants, sucrose synthase (SUS, EC 2.4.1.13) is widely considered a multifunctional protein involved in modulating sink strength, cellulose biosynthesis, and carbon partitioning. However, supporting genetic evidence regarding the role of SUS from bamboo in fiber development is lacking. Here, we obtained transgenic poplar lines overexpressing the bamboo BeSUS5 gene and conducted functional analysis. We found that overexpression of BeSUS5 enhanced the activity of SUS and significantly promoted the growth of the plants, especially xylem growth. In BeSUS5 overexpressed poplar plants, the total soluble sugar (TSS) and starch contents were decreased in leaves, while the cellulose content was increased in stems, indicating that overexpression of BeSUS5 might enhance the partitioning of carbon to cellulose in poplar. Consistent with these results, the expression of cellulose biosynthesis and phloem loading–related genes, such as cellulose synthase (CesA7), KORRIGAN (KOR), and sucrose transporter (SUT1), was upregulated in transgenic plants. As a result, transgenic poplars displayed not only an increase in cell wall thickness and cell wall crystallinity but also an altered stem fiber phenotype. Taken together, our results imply the vast potential of BeSUS5 for the genetic improvement of wood cellulose production and fiber quality.