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Natural genetic variation for expression of a SWEET transporter among wild species of Solanum lycopersicum (tomato) determines the hexose composition of ripening tomato fruit
Author(s) -
Shammai Arik,
Petreikov Marina,
Yeselson Yelena,
Faigenboim Adi,
MoyKomemi Michal,
Cohen Shahar,
Cohen Dvir,
Besaulov Eduard,
Efrati Ari,
Houminer Naomi,
Bar Moshe,
Ast Tslil,
Schuldiner Maya,
Klemens P.A.W.,
Neuhaus Ekkehard,
Baxter Charles J.,
Rickett Dan,
Bonnet Julien,
White Ruth,
Giovani James J.,
Levin Ilan,
Schaffer Arthur
Publication year - 2018
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.14035
Subject(s) - fructose , sucrose , solanum , sugar , hexose , glucose transporter , biochemistry , biology , genetically modified tomato , ripening , gene , botany , food science , transgene , genetically modified crops , enzyme , microbiology and biotechnology , insulin
Summary The sugar content of Solanum lycopersicum (tomato) fruit is a primary determinant of taste and quality. Cultivated tomato fruit are characterized by near‐equimolar levels of the hexoses glucose and fructose, derived from the hydrolysis of translocated sucrose. As fructose is perceived as approximately twice as sweet as glucose, increasing its concentration at the expense of glucose can improve tomato fruit taste. Introgressions of the Fgr H allele from the wild species Solanum habrochaites ( LA 1777) into cultivated tomato increased the fructose‐to‐glucose ratio of the ripe fruit by reducing glucose levels and concomitantly increasing fructose levels. In order to identify the function of the Fgr gene, we combined a fine‐mapping strategy with RNA seq differential expression analysis of near‐isogenic tomato lines. The results indicated that a SWEET protein was strongly upregulated in the lines with a high fructose‐to‐glucose ratio. Overexpressing the SWEET protein in transgenic tomato plants dramatically reduced the glucose levels and increased the fructose : glucose ratio in the developing fruit, thereby proving the function of the protein. The SWEET protein was localized to the plasma membrane and expression of the SlFgr gene in a yeast line lacking native hexose transporters complemented growth with glucose, but not with fructose. These results indicate that the SlFgr gene encodes a plasma membrane‐localized glucose efflux transporter of the SWEET family, the overexpression of which reduces glucose levels and may allow for increased fructose levels. This article identifies the function of the tomato Fgr gene as a SWEET transporter, the upregulation of which leads to a modified sugar accumulation pattern in the fleshy fruit. The results point to the potential of the inedible wild species to improve fruit sugar accumulation via sugar transport mechanisms.