Integrating Sugar Metabolism With Transport: Elevation of Endogenous Cell Wall Invertase Activity Up-Regulates SlHT2 and SlSWEET12c Expression for Early Fruit Development in Tomato.

Lei Ru,John W Patrick,Zhujun Zhu,Yong He,Yong-Ling Ruan

doi:10.3389/fgene.2020.592596

Lei Ru, John W Patrick + Show 3 more

Open Access

https://doi.org/10.3389/fgene.2020.592596

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Abstract

Early fruit development is critical for determining crop yield. Cell wall invertase (CWIN) and sugar transporters both play important roles in carbon allocation and plant development. However, there is little information about the relationship between CWIN and those functionally related sugar transporters during fruit development. By using transgenic tomato with an elevated CWIN activity, we investigated how an increase in CWIN activity may regulate the expression of sugar transporter genes during fruit development. Our analyses indicate that CWIN activity may be under tight regulation by multiple regulators, including two invertase inhibitors (INVINHs) and one defective CWIN (deCWIN) in tomato ovaries prior to anthesis. Among the sugar transporters, expression of SlSWEET12c for sucrose efflux and SlHT2 for hexose uptake was enhanced by the elevated CWIN activity at 10 and 15 days after anthesis of tomato fruit development, respectively. The findings show that some specific sugars will eventually be exported transporters (SWEETs) and hexose transporters (HTs) respond to elevate CWIN activity probably to promote rapid fruit expansion when sucrose efflux from phloem and hexose uptake by parenchyma cell are in high demand. The analyses provide new leads for improving crop yield by manipulating CWIN-responsive sugar transporters, together with CWIN itself, to enhance fruit development and sugar accumulation.

Highlights

Tomato is one of the most important fleshy fruit crops globally (Schwarz et al, 2014)
Cell wall invertase activity may be regulated by invertase inhibitors (INVINHs) and defective CWIN together at the posttranslational level (Palmer et al, 2015)
SldeCWIN1 is another potential regulator for regulating CWIN activity at post-translational level (Palmer et al, 2015) with its expression was only detected in 2 dba ovaries and sink leaves (Figure 1A)

Summary

Introduction

Tomato is one of the most important fleshy fruit crops globally (Schwarz et al, 2014). Ovary and young fruits are typical carbon sinks, which require sugars transported from source leaves In these sinks, sucrose can be unloaded into sink cells through either symplasmic or apoplasmic unloading or both simultaneously (Patrick, 1997; Patrick et al, 2001). In tomato fruit, unloading shifts from an apoplasmic route in the ovary wall to a symplasmic pathway in the pericarp of young fruit (Jin et al, 2009; Palmer et al, 2015) before switching to an apoplasmic route in the pericarp at the onset of the rapid phase of hexose accumulation (Ruan and Patrick, 1995). The sugar transporters include sucrose transporters (SUTs), hexose transporters (HTs), as well as sugars will eventually be exported transporters (SWEETs)

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