Abstract
Sucrose phosphate synthase (SPS) is a key enzyme in sucrose synthesis, which controls sucrose content in plants. This study was designed to examine the efficacy of the overexpression of SoSPS1 gene on sucrose accumulation and carbon partitioning in transgenic sugarcane. The overexpression of SoSPS1 gene increased SPS activity and sucrose content in transgenic sugarcane leaves. More importantly, the overexpression enhanced soluble acid invertase (SAI) activity concomitant with the increase of glucose and fructose levels in the leaves, whereas sucrose synthase activity exhibited almost no change. In the stalk, a similar correlation was observed, but a higher correlation was noted between SPS activity and sugar content. These results suggest that SPS overexpression has both direct and indirect effects on sugar concentration and SAI activity in sugarcane. In addition, SPS overexpression resulted in a significant increase in plant height and stalk number in some transgenic lines compared to those in non-transgenic control. Taken together, these results strongly suggest that enhancing SPS activity is a useful strategy for improving sugarcane yield.
Highlights
Sugarcane (Saccharum officinarum), a C4 plant, is a major crop for sucrose production in tropical and sub-tropical areas
To confirm the insertion of the transgene of pBI121-SoSPS1 construct, genome DNA was isolated from the leaves of one-month-old transgenic and non-transgenic (NT)
We confirmed a single hybridization band of the nptII transgene in a Southern blot analysis (Figure S3). These results show that the transgene was properly inserted into the sugarcane genome
Summary
Sugarcane (Saccharum officinarum), a C4 plant, is a major crop for sucrose production in tropical and sub-tropical areas. Sucrose is synthesized via photosynthesis in the leaf, after which it is transported to, and accumulates in, the stalk. Sucrose metabolism in plants involves several enzymes, such as sucrose phosphate synthase (SPS; EC 2.4.2.14), sucrose synthase (SuSy; EC 2.4.1.13), and invertase (EC 3.2.1.26). SPS is a key enzyme for sucrose synthesis from uridine diphosphate-glucose (UDPG) and fructose-6 phosphate (F6P). SuSy catalyzes reversible reactions: either synthesis or cleavage of sucrose with UDPG and fructose; it is mostly present in non-growing sink tissue and plays a role in the sucrose degradation pathway [1]. There are several isoforms of invertase, the major ones being the vacuolar and cell wall invertases that cleave sucrose to glucose and fructose under weak acidic conditions
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