Rapid pollen tube growth requires uptake of Suc or its hydrolytic products, hexoses, from the apoplast of surrounding tissues in the style. Due to species-specific sugar requirements, reliance of pollen germination and tube growth on cell wall invertase and Suc or hexose transporters varies between species, but it is not known if plants have a sugar transporter that mediates the uptake of both hexose and Suc for pollen tube growth. Here, we show that a sugar transporter protein in apple (Malus domestica), MdSTP13a, takes up both hexose and Suc when expressed in yeast, and is essential for pollen tube growth on Glc and Suc but not on maltose. MdSTP13a-mediated direct uptake of Suc is primarily responsible for apple pollen tube growth on Suc medium. Sorbitol, a major photosynthate and transport carbohydrate in apple, modulates pollen tube growth via the MYB transcription factor MdMYB39L, which binds to the promoter of MdSTP13a to activate its expression. Antisense repression of MdSTP13a blocks sorbitol-modulated pollen tube growth. These findings demonstrate that MdSTP13a takes up both hexose and Suc for sorbitol-modulated pollen tube growth in apple, revealing a situation where acquisition of sugars for pollen tube growth is regulated by a sugar alcohol.

中文翻译：

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糖转运蛋白吸收己糖和蔗糖，用于山梨醇调节的苹果体外花粉管生长。

花粉管的快速生长需要从花粉管周围组织的质外体中摄取 Suc 或其水解产物己糖。由于物种特异性的糖需求，花粉萌发和管生长对细胞壁转化酶和 Suc 或己糖转运蛋白的依赖因物种而异，但尚不清楚植物是否具有介导花粉摄取己糖和 Suc 的糖转运蛋白管生长。在这里，我们发现苹果（Malus Domestica）中的糖转运蛋白 MdSTP13a 在酵母中表达时会吸收己糖和 Suc，并且对于花粉管在 Glc 和 Suc 上生长至关重要，但在麦芽糖上则不然。MdSTP13a 介导的 Suc 直接摄取主要负责苹果花粉管在 Suc 培养基上的生长。山梨醇是苹果中的主要光合产物和运输碳水化合物，通过 MYB 转录因子 MdMYB39L 调节花粉管生长，该因子与 MdSTP13a 的启动子结合以激活其表达。MdSTP13a 的反义抑制可阻断山梨醇调节的花粉管生长。这些发现表明，MdSTP13a 吸收己糖和 Suc 来调节苹果花粉管的生长，揭示了花粉管生长所需糖的获取受到糖醇调节的情况。