Abstract
Starch is an important component in lotus. ABA is an important plant hormone, which plays a very crucial role in regulating plant starch synthesis. Using ‘MRH’ as experimental materials, the leaves were sprayed with exogenous ABA before the rhizome expansion. The results showed that stomatal conductance and transpiration rate decreased while net photosynthetic rate increased. The total starch content of the underground rhizome of lotus increased significantly. Meanwhile, qPCR results showed that the relative expression levels of NnSS1, NnSBE1 and NnABI4 were all upregulated after ABA treatment. Then, yeast one-hybrid and dual luciferase assay suggested that NnABI4 protein can promote the expression of NnSS1 by directly binding to its promoter. In addition, subcellular localization results showed that NnABI4 encodes a nuclear protein, and NnSS1 protein was located in the chloroplast. Finally, these results indicate that ABA induced the upregulated expression of NnABI4, and NnABI4 promoted the expression of NnSS1 and thus enhanced starch accumulation in lotus rhizomes. This will provide a theoretical basis for studying the molecular mechanism of ABA regulating starch synthesis in plant.
Highlights
Starch is the main storage form of carbohydrate in higher plants and occupies an important position in the human diet [1]
The biosynthesis of plant starch is a complex metabolic process, which requires the synergy of multiple enzymes, including ADP glucose pyrophosphorylase (AGPase), granule bound starch synthase (GBSS), soluble starch synthase (SSS) and starch branching enzyme (SBE) [9,10]
SSSII and SSSIII are mainly involved in the synthesis of longer chains [13], while SSSIV may be involved in the formation of starch granules [14]
Summary
Starch is the main storage form of carbohydrate in higher plants and occupies an important position in the human diet [1]. According to the different molecular structure, starch mainly includes two glucose polymers: amylose and amylopectin [8]. The biosynthesis of plant starch is a complex metabolic process, which requires the synergy of multiple enzymes, including ADP glucose pyrophosphorylase (AGPase), granule bound starch synthase (GBSS), soluble starch synthase (SSS) and starch branching enzyme (SBE) [9,10]. AGPase catalyzes glucose 1-phosphate and ATP to synthesize ADPG, the precursor substance of starch synthesis [11]. SSS and SBE are mainly involved in amylose synthesis. SSSII and SSSIII are mainly involved in the synthesis of longer chains [13], while SSSIV may be involved in the formation of starch granules [14]. SBE can branch starch chain and contribute to the synthesis of
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