Characterization of a vacuolar sucrose transporter, HbSUT5, from Hevea brasiliensis: involvement in latex production through regulation of intracellular sucrose transport in the bark and laticifers
Characterization of a vacuolar sucrose transporter, HbSUT5, from Hevea brasiliensis: involvement in latex production through regulation of intracellular sucrose transport in the bark and laticifers
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DOI：
10.1186/s12870-019-2209-9
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发表时间：
2019-12-27
影响因子：
5.3
通讯作者：
Tang, Chaorong
中科院分区：
文献类型：
--
作者：
Long, Xiangyu;Li, Heping;Tang, Chaorong
背景蔗糖（Suc）作为巴西橡胶树中橡胶生物合成的前体分子，通过韧皮部介导的长距离运输从叶子运输到树干树皮中的乳管，其中乳胶（乳管的细胞质）被提取为橡胶。在我们之前的报告中，已经在橡胶树中克隆了六个Suc转运蛋白（SUT）基因，其中HbSUT3被证实在Suc装载到乳管中发挥积极作用。在本研究中，另一种乳胶丰富的 SUT 亚型 HbSUT5，其表达量仅次于 HbSUT3，特别是其在乳胶生产中的作用。结果系统发育分析和亚细胞定位均将 HbSUT5 鉴定为 SUT4 分支（= III 型）下的液泡膜定位 SUT 蛋白。面包酵母中的 Suc 摄取测定表明，HbSUT5 是典型的 Suc-H+ 同向转运蛋白，但其对 Suc 的高亲和力（Km=2.03mM，pH5.5）以及转运 Suc 和麦芽糖的相似效率使其成为 SUT4 分支下的特殊 SUT。在转录本水平上，HbSUT5 在橡胶树皮中大量且优先表达。通过割胶和乙烯利两种增产处理，橡胶树乳胶和树皮中的 HbSUT5 转录物均显着减少，其模式与 HbSUT3 相反。在乙烯利处理下，乳胶胞质溶胶中的 Suc 水平显着降低，但乳胶 luoids（多分散液泡）中的 Suc 水平变化很小，这表明 HbSUT5 表达降低在 luoids 中的 Suc 区室化中发挥作用，从而增强了乳胶管中的 Suc 库强度。结论我们的研究结果为液泡蔗糖转运蛋白 HbSUT5 在 Suc 交换中的作用提供了见解。产橡胶的乳管中的鲁类化合物和胞质溶胶。
BackgroundSucrose (Suc), as the precursor molecule for rubber biosynthesis in Hevea brasiliensis, is transported via phloem-mediated long-distance transport from leaves to laticifers in trunk bark, where latex (cytoplasm of laticifers) is tapped for rubber. In our previous report, six Suc transporter (SUT) genes have been cloned in Hevea tree, among which HbSUT3 is verified to play an active role in Suc loading to the laticifers. In this study, another latex-abundant SUT isoform, HbSUT5, with expressions only inferior to HbSUT3 was characterized especially for its roles in latex production.ResultsBoth phylogenetic analysis and subcellular localization identify HbSUT5 as a tonoplast-localized SUT protein under the SUT4-clade (=type III). Suc uptake assay in baker's yeast reveals HbSUT5 to be a typical Suc-H+ symporter, but its high affinity for Suc (Km=2.03mM at pH5.5) and the similar efficiency in transporting both Suc and maltose making it a peculiar SUT under the SUT4-clade. At the transcript level, HbSUT5 is abundantly and preferentially expressed in Hevea barks. The transcripts of HbSUT5 are conspicuously decreased both in Hevea latex and bark by two yield-stimulating treatments of tapping and ethephon, the patterns of which are contrary to HbSUT3. Under the ethephon treatment, the Suc level in latex cytosol decreases significantly, but that in latex lutoids (polydispersed vacuoles) changes little, suggesting a role of the decreased HbSUT5 expression in Suc compartmentalization in the lutoids and thus enhancing the Suc sink strength in laticifers.ConclusionsOur findings provide insights into the roles of a vacuolar sucrose transporter, HbSUT5, in Suc exchange between lutoids and cytosol in rubber-producing laticifers.