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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Sucrose Transporter StSUT4 from Potato Affects Flowering, Tuberization, and Shade Avoidance Response^1,[W]

Institute of Biology, Plant Physiology, Humboldt University, 10115 Berlin, Germany (I.A.C., J.L., U.K., B.G., C.K.); and Max Planck Institut für Molekulare Pflanzenphysiologie, 14476 Potsdam-Golm, Germany (J.M., P.G.)

Sucrose (Suc) transporters belong to a large gene family. The physiological role of SUT1 proteins has been intensively investigated in higher plants, whereas that of SUT4 proteins is so far unknown. All three known Suc transporters from potato (Solanum tuberosum), SUT1, SUT2, and SUT4, are colocalized and their RNA levels not only follow a diurnal rhythm, but also oscillate in constant light. Here, we examined the physiological effects of transgenic potato plants on RNA interference (RNAi)-inactivated StSUT4 expression. The phenotype of StSUT4-RNAi plants includes early flowering, higher tuber production, and reduced sensitivity toward light enriched in far-red wavelength (i.e. in canopy shade). Inhibition of StSUT4 led to tuber production of the strict photoperiodic potato subsp. andigena even under noninductive long-day conditions. Accumulation of soluble sugars and Suc efflux from leaves of transgenic plants are modified in StSUT4-RNAi plants, leading to modified Suc levels in sink organs. StSUT4 expression of wild-type plants is induced by gibberellins and ethephon, and external supply of gibberellic acid leads to even more pronounced differences between wild-type and StSUT4-RNAi plants regarding tuber yield and internode elongation, indicating a reciprocal regulation of StSUT4 and gibberellins.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Christina Kühn (christina.kuehn{at}biologie.hu-berlin.de).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.112334

^* Corresponding author; e-mail christina.kuehn{at}biologie.hu-berlin.de.

Received November 2, 2007; accepted December 6, 2007; published December 14, 2007.

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