The H+-pyrophosphatase IbVP1 regulates carbon flux to influence the starch metabolism and yield of sweet potato

Weijuan Fan,Jun Yang,Peng Zhang,Hongxia Wang,Yandi Zhang,Ling Yuan,Wenzhi Zhou,Yinliang Wu

doi:10.1038/s41438-020-00454-2

Abstract

Storage roots of sweet potato are important sink organs for photoassimilates and energy, and carbohydrate metabolism in storage roots affects yield and starch production. Our previous study showed that sweet potato H+-pyrophosphatase (IbVP1) plays a vital role in mitigating iron deficiency and positively controls fibrous root growth. However, its roles in regulating starch production in storage roots have not been investigated. In this study, we found that IbVP1 overexpression in sweet potato improved the photosynthesis ability of and sucrose content in source leaves and increased both the starch content in and total yield of sink tissues. Using 13C-labeled sucrose feeding, we determined that IbVP1 overexpression promotes phloem loading and sucrose long-distance transport and enhances Pi-use efficiency. In sweet potato plants overexpressing IbVP1, the expression levels of starch biosynthesis pathway genes, especially AGPase and GBSSI, were upregulated, leading to changes in the structure, composition, and physicochemical properties of stored starch. Our study shows that the IbVP1 gene plays an important role in regulating starch metabolism in sweet potato. Application of the VP1 gene in genetic engineering of sweet potato cultivars may allow the improvement of starch production and yield under stress or nutrient-limited conditions.

Highlights

Sweet potato (Ipomoea batatas (L.) Lam.) is a multifunctional starchy root crop species that is a primary resource for food, feed, and bioindustrial applications
The sucrose contents in the leaves of the IA lines were higher than those in the WT (Fig. 2d). Consistent with these findings, more 13C-labeled sucrose was detected in the fibrous roots of IA plants compared with the WT, indicating an increase in the rate of sucrose transport out of leaves of the IA lines (Fig. 2e). These results clearly demonstrate that the transgenic IA lines are more efficient at exporting carbohydrates, mainly sucrose, from photosynthetic leaves, promoting the yield of storage roots via upregulation of IbVP1 expression
We found that the expression levels of the AGPase, granule-bound starch synthase I (GBSSI), SSI, SBEI, and SBEII genes were upregulated in the transgenic lines (Fig. 4a)

Summary

Introduction

Sweet potato (Ipomoea batatas (L.) Lam.) is a multifunctional starchy root crop species that is a primary resource for food, feed, and bioindustrial applications. The annual global production of sweet potato is approximately 92 million tons of fresh storage roots (FAOSTAT 2018), which is crucial for food security, malnutrition and poverty alleviation, and bioindustrial development[1,2]. With increasing demand for sweet potato production, storage roots need to be improved, Sucrose transporters (SUTs) are responsible for sucrose loading into the complex comprising phloem sieve elements and companion cells. Overexpression of the H+-translocating inorganic pyrophosphatase (H+-PPase) gene IbVP1 increases plasma membrane H+-ATPase hydrolytic activities, SUT1 expression, and root growth[11]. How IbVP1 regulates starch metabolism in sweet potato storage roots has not yet been determined

Methods

Results

Conclusion