Abstract
The starch properties of the storage root (SR) affect the quality of sweet potato (Ipomoea batatas (L.) Lam.). Although numerous studies have analyzed the accumulation and properties of starch in sweet potato SRs, the transcriptomic variation associated with starch properties in SR has not been quantified. In this study, we measured the starch and sugar contents and analyzed the transcriptome profiles of SRs harvested from sweet potatoes with high, medium, and extremely low starch contents, at five developmental stages [65, 80, 95, 110, and 125 days after transplanting (DAP)]. We found that differences in both water content and starch accumulation in the dry matter affect the starch content of SRs in different sweet potato genotypes. Based on transcriptome sequencing data, we assembled 112336 unigenes, and identified several differentially expressed genes (DEGs) involved in starch and sucrose metabolism, and revealed the transcriptional regulatory network controlling starch and sucrose metabolism in sweet potato SRs. Correlation analysis between expression patterns and starch and sugar contents suggested that the sugar–starch conversion steps catalyzed by sucrose synthase (SuSy) and UDP-glucose pyrophosphorylase (UGPase) may be essential for starch accumulation in the dry matter of SRs, and IbβFRUCT2, a vacuolar acid invertase, might also be a key regulator of starch content in the SRs. Our results provide valuable resources for future investigations aimed at deciphering the molecular mechanisms determining the starch properties of sweet potato SRs.
Highlights
Sweet potato (Ipomoea batatas (L.) Lam.) is an important food crop that is widely grown throughout the world due to its stable yield, rich nutrient content, low input requirement, multiple uses, high yield potential, and adaptability under a range of environmental conditions (Ahn et al, 2010; Cervantes-Flores et al, 2011; Wang et al, 2011)
We found that the storage root (SR) dry matter and starch content varied greatly among genotypes, but that for each genotype, these traits were relatively stable among different planting years or environments, and the genotype had a larger effect than did the environment on these traits (Lu et al, 2015; Zhang et al, 2016)
The dry matter of sweet potato SRs consists of sugar, starch, fat, and other minor components, but starch accounts for the largest portion (50–80%) of the dry matter in SRs (Rukundo et al, 2013; Zhou et al, 2015)
Summary
Sweet potato (Ipomoea batatas (L.) Lam.) is an important food crop that is widely grown throughout the world due to its stable yield, rich nutrient content, low input requirement, multiple uses, high yield potential, and adaptability under a range of environmental conditions (Ahn et al, 2010; Cervantes-Flores et al, 2011; Wang et al, 2011). Starch Metabolism in Storage Root economically important physiological process in sweet potato production. This process includes the adventitious roots arising from vegetative cuttings, fibrous roots (FRs) development and some of FRs subsequently developing into SRs, which accompanied with SRs swell up and weight increases through accumulating photosynthates and massive filling with starch (Ravi et al, 2009; Firon et al, 2013). Starch is the major component of the SR, accounting for 50– 80% of its dry matter (Rukundo et al, 2013; Zhou et al, 2015) This high level of starch renders sweet potato a good source of carbohydrates, and an excellent raw material for starch-based industries and biofuel production. As producing biofuel from biomass offers a renewable approach for reducing the consumption of crude oil, greenhouse gas emissions, and other environmental pollutants, and for offsetting climate change, global warming, and air pollution (Demirbas, 2009; Jacobson, 2009), methods to improve the quality of sweet potato as a feedstock for ethanol production should be investigated
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