The main phloem loader in potato, sucrose transporter StSUT1, is co-expressed with two members of the SWEET gene family: StSWEET11b, a clade III member of SWEET carriers assumed to be involved in sucrose efflux, and StSWEET1g, a clade I member involved in glucose efflux into the apoplast that physically interacts with StSUT1. We investigated the functionality of SWEET carriers via uptake experiments with fluorescent glucose or sucrose analogs. Inhibition or overexpression of StSWEET1g/SlSWEET1e affected tuberization and flowering in transgenic potato plants. Isolation of the apoplasmic fluid by vacuum infiltration centrifugation revealed changes in the apoplasmic hexose composition and mono-to-disaccharide ratio, affecting sink strength. Down-regulation of StSWEET1g expression affected the expression of SP6A, a tuberigen, and miR172 under LD conditions, leading to early flowering and tuberization. A systematic screen for StSWEET1g-interacting protein partners revealed several proteins affecting cell wall integrity and strengthening. StSWEET1g and the main interaction partners were strongly down-regulated during tuber development. We discuss whether StSWEET1g activity might be linked to cell wall remodeling during tuber development and the switch from apoplasmic to symplasmic phloem unloading.

中文翻译：

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马铃薯糖转运蛋白 SWEET1g 影响质粒糖比例和韧皮部移动块茎和花诱导信号


马铃薯中的主要韧皮部加载体，蔗糖转运蛋白 StSUT1，与 SWEET 基因家族的两个成员共表达：StSWEET11b，假设参与蔗糖外排的 SWEET 载体的进化枝 III 成员，以及 StSWEET1g，参与葡萄糖外排到质外泌体的进化枝 I 成员，与 StSUT1 物理相互作用。我们通过荧光葡萄糖或蔗糖类似物的摄取实验研究了 SWEET 载体的功能。StSWEET1g/SlSWEET1e 的抑制或过表达影响转基因马铃薯植株的块茎化和开花。通过真空浸润离心分离质外质液揭示了质外质己糖组成和单糖与二糖比率的变化，从而影响了下沉强度。在 LD 条件下，StSWEET1g 表达的下调影响了 SP6A 、 一种块茎根和 miR172 的表达，导致早期开花和块茎化。对 StSWEET1g 相互作用蛋白伴侣的系统筛选揭示了几种影响细胞壁完整性和强化的蛋白质。StSWEET1g 和主要相互作用伴侣在块茎发育过程中强烈下调。我们讨论了 StSWEET1g 活性是否可能与块茎发育过程中的细胞壁重塑以及从质外质到共质韧皮部卸载的转变有关。