Abstract

Translocation and long-distance transport of phytohormones are considered important processes for phytohormone responses, as well as their synthesis and signaling. Here, we report on the dual function of OsSWEET3a, a bidirectional sugar transporter from clade I of the rice SWEET family of proteins, as both a gibberellin (GA) and a glucose transporter. OsSWEET3a efficiently transports GAs in the C13-hydroxylation pathway of GA biosynthesis. Both knockout and overexpression lines of OsSWEET3a showed defects in germination and early shoot development, which were partially restored by GA, especially GA₂₀. Quantitative reverse transcription PCR, GUS staining and in situ hybridization revealed that OsSWEET3a was expressed in vascular bundles in basal parts of the seedlings. OsSWEET3a expression was co-localized with OsGA20ox1 expression in the vascular bundles but not with OsGA3ox2, whose expression was restricted to leaf primordia and young leaves. These results suggest that OsSWEET3a is expressed in the vascular tissue of basal parts of seedlings and is involved in the transport of both GA₂₀ and glucose to young leaves, where GA₂₀ is possibly converted to the bioactive GA₁ form by OsGA3ox2, during early plant development. We also indicated that such GA transport activities of SWEET proteins have sporadically appeared in the evolution of plants: GA transporters in Arabidopsis have evolved from sucrose transporters, while those in rice and sorghum have evolved from glucose transporters.

中文翻译：

---

OsSWEET3a作为赤霉素和葡萄糖转运蛋白的双重功能对于水稻幼芽的发育很重要

摘要

植物激素的转运和长距离运输被认为是植物激素反应及其合成和信号传导的重要过程。在这里，我们报道了OsSWEET3a的双重功能，OsSWEET3a是来自水稻SWEET蛋白质家族的进化枝I的双向糖转运蛋白，既有赤霉素（GA）又有葡萄糖转运蛋白。OsSWEET3a在GA生物合成的C13-羟基化途径中有效转运GA。OsSWEET3a的敲除和过表达系均显示出发芽和早期芽发育中的缺陷，GA，尤其是GA _20可以部分修复这些缺陷。定量逆转录PCR，GUS染色和原位杂交表明，OsSWEET3a在幼苗基部的维管束中表达。OsSWEET3a表达与血管束中的OsGA20ox1表达共定位，但不与OsGA3ox2共定位，OsGA3ox2的表达限于叶片原基和幼叶。这些结果表明，OsSWEET3a在幼苗基部的维管组织中表达，并参与了GA ₂₀和葡萄糖向幼叶的转运，其中GA ₂₀可能转化为具有生物活性的GA ₁在植物早期发育中由OsGA3ox2形成。我们还表明，这种SWEET蛋白的GA转运活性偶发出现在植物的进化中：拟南芥中的GA转运蛋白是从蔗糖转运蛋白演变而来的，水稻和高粱中的GA转运蛋白是从葡萄糖转运蛋白演变而来的。