Sucrose transporter LeSUT1 and LeSUT2 inhibition affects tomato fruit development in different ways

Abstract

SummarySucrose transporters of higher plants belong to a large gene family. At least four different sucrose transporters are known in Solanaceous plants, although their function remains to be elucidated in detail. The isolation of LeSUT1 and LeSUT2 from Lycopersicon esculentum has been described earlier. Whereas SUT1 is supposed to be the main phloem loader of sucrose in Solanaceae, the role of SUT2 remains a matter of debate. A transgenic approach was taken to evaluate the potential functions of SUT2/SUC3 proteins in sucrose transport or sensing. Expression of LeSUT1 and LeSUT2 was inhibited independently in transgenic tomato plants, using the antisense technique, in order to analyse their specific functions. Although the phloem-specific inhibition of LeSUT1 antisense plants showed a phenotype consistent with an essential role in phloem loading, constitutive LeSUT2 antisense inhibition exclusively affected tomato fruit and seed development. Neither LeSUT1, nor the LeSUT2 antisense plants were able to produce normal tomato fruits; however, it is likely that independent mechanisms underlie these phenomena. While phloem loading was blocked in LeSUT1 antisense plants, the fertility of fruits was reduced in LeSUT2 antisense plants. A detailed physiological analysis of these plants established a role for SUT2 in pollen tube growth and thus assigned a physiological role for SUT2.

Expression of Sucrose Transporter cDNAs Specifically in Companion Cells Enhances Phloem Loading and Long-Distance Transport of Sucrose but Leads to an Inhibition of Growth and the Perception of a Phosphate Limitation

“…AtSUC9 has the highest affinity for Suc among the plant SUTs, and the encoding gene is expressed broadly in sink organs, whereas NtSUT3 and LeSUT1 are the major transporters for phloem loading in the Solanaceae species tobacco and tomato (Lemoine et al, 1999;Hackel et al, 2006;Weise et al, 2008). One possible explanation for the lack of complementation is that these constructs are not expressed at a high enough level.…”

An investigation of differences in fruit yield and components contributing to increased fruit yield in Japanese and Dutch tomato cultivars

“…This gene encodes the major isoform of the sucrose transporter in photosynthetic source leaves, which functions in phloem loading of sucrose in tomato plants (Kühn et al 1997;Hackel et al 2006;Yin et al 2010). No significant difference in LeSUT1 transcriptional level was observed between the cultivars at 10, 30, or 50 DAF.…”

Regulation of Sucrose Transporters and Phloem Loading in Response to Environmental Cues

“…To test how SUT gene expression corresponds to protein abundance, we performed western blots using protein extracts of the same leaf material as for qPCR and an antibody against tomato LeSUT1 with proven binding specificity (Hackel et al, 2006). Even though expression of LeSUT1 did not change significantly in response to exposure to high light, low light, or dark conditions, protein abundance showed strong differences.…”