Effects of chrysolaminarin synthase knockdown in the diatom Thalassiosira pseudonana: Implications of reduced carbohydrate storage relative to green algae

In all organisms, the flux of carbon through the fundamental pathways of glycolysis, gluconeogenesis and the pyruvate hub is a core process related to growth and productivity. In unicellular microalgae, the complexity and intracellular location of specific steps of these pathways can vary substantially. In addition, the location and chemical nature of storage carbohydrate can be substantially different. The role of starch storage in green algae has been investigated, but thus far, only a minimal understanding of the role of carbohydrate storage in diatoms as the beta- 1,3-glucan chrysolaminarin has been achieved. In this report, we aimed to determine the effect of specifically reducing the ability of Thalassiosira pseudonana cells to accumulate chrysolaminarin by knocking down transcript levels of the chrysolaminarin synthase gene. We monitored changes in chrysolaminarin and triacylglycerol (TAG) levels during growth and silicon starvation. Transcript- level changes in genes encoding steps in chrysolaminarin metabolism, and cytoplasmic and chloroplast glycolysis/ gluconeogenesis, were monitored during silicon limitation, highlighting the carbon flux processes involved. We demonstrate that knockdown lines accumulate less chrysolaminarin and have a transiently increased TAG level, with minimal detriment to growth. The results provide insight into the role of chrysolaminarin storage in diatoms, and further discussion highlights differences between diatoms and green algae in carbohydrate storage processes and the effect of reducing carbohydrate stores on growth and productivity. (c) 2017 The Authors. Published by Elsevier B.V.