Seed development and yield depend on the transport and supply of sugar. However, an insufficient supply of nutrients from maternal tissues to embryos results in seed abortion and yield reduction in Camellia oleifera. In this study, we systematically examined the route and regulatory mechanisms of sugar import into developing C. oleifera seeds using a combination of histological observations, transcriptome profiling and functional analysis. Labelling with the tracer carboxyfluorescein revealed a symplasmic route in the integument and an apoplasmic route for post-phloem transport at the maternal-filial interface. Enzymatic activity and histological observation showed that at early stages (180-220 DAP) of embryo differentiation, the high hexose/sucrose ratio was primarily mediated by acid invertases and the micropylar endosperm/suspensor provides a channel for sugar import. Through Camellia genomic profiling, we identified three plasma membrane-localized proteins including CoSWEET1b, CoSWEET15 and CoSUT2 and one tonoplast-localized protein CoSWEET2a in seeds and verified their ability to transport various sugars via transformation in yeast mutants and calli. In situ hybridization and profiling of glycometabolism-related enzymes further demonstrated that CoSWEET15 functions as a micropylar endosperm-specific gene, together with the cell wall acid invertase CoCWIN9, to support early embryo development, while CoSWEET1b, CoSWEET2a and CoSUT2 function at transfer cells and chalazal nucellus coupled with CoCWIN9 and CoCWIN11 responsible for sugar entry in bulk into the filial tissue. Collectively, our findings provide the first comprehensive evidence of the molecular regulation of sugar import into and within C. oleifera seeds and provide a new target for manipulating seed development.

中文翻译：

---

油茶种子发育中糖转运蛋白和细胞壁转化酶介导的糖输入


种子的发育和产量取决于糖的运输和供应。然而，母体组织向胚胎提供的营养不足，会导致油茶种子败育和产量降低。在这项研究中，我们结合组织学观察、转录组分析和功能分析，系统地研究了糖输入到正在发育的油茶种子中的途径和调控机制。用示踪剂羧基荧光素标记揭示了珠被中的共质途径和母子界面处韧皮部后运输的质外质途径。酶活性和组织学观察表明，在胚胎分化的早期阶段（180-220 DAP），高己糖/蔗糖比例主要由酸性转化酶介导，珠孔胚乳/胚柄提供了糖输入的通道。通过油茶基因组分析，我们在种子中鉴定了三种质膜定位蛋白，包括 CoSWEET1b、CoSWEET15 和 CoSUT2 以及一种液泡膜定位蛋白 CoSWEET2a，并验证了它们通过酵母突变体和愈伤组织中的转化转运各种糖的能力。原位杂交和糖代谢相关酶的分析进一步证明，CoSWEET15 作为珠孔胚乳特异性基因，与细胞壁酸性转化酶 CoCWIN9 一起支持早期胚胎发育，而 CoSWEET1b、CoSWEET2a 和 CoSUT2 在转移细胞和合点处发挥作用nucellus 与 CoCWIN9 和 CoCWIN11 结合负责糖大量进入子代组织。总的来说，我们的研究结果提供了第一个全面的证据，证明糖输入到C. 油茶种子并为操纵种子发育提供了新的目标。