Apple ALMT9 Requires a Conserved C-Terminal Domain for Malate Transport Underlying Fruit Acidity.,Plant Physiology

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Apple ALMT9 Requires a Conserved C-Terminal Domain for Malate Transport Underlying Fruit Acidity.
Plant Physiology ( IF 6.5 ) Pub Date : 2019-11-26 , DOI: 10.1104/pp.19.01300
Chunlong Li ₁ , Laura Dougherty ₂ , Alison E Coluccio ₃ , Dong Meng ₁ , Islam El-Sharkawy ₂ , Ewa Borejsza-Wysocka _{1,

2} , Dong Liang ₂ , Miguel A Piñeros _{3,

4} , Kenong Xu ₂ , Lailiang Cheng ₅

Affiliation

Malate accumulation in the vacuole largely determines apple (Malus domestica) fruit acidity, and low fruit acidity is strongly associated with truncation of Ma1, an ortholog of ALUMINUM-ACTIVATED MALATE TRANSPORTER9 (ALMT9) in Arabidopsis (Arabidopsis thaliana). A mutation at base 1,455 in the open reading frame of Ma1 leads to a premature stop codon that truncates the protein by 84 amino acids at its C-terminal end. Here, we report that both the full-length protein, Ma1, and its naturally occurring truncated protein, ma1, localize to the tonoplast; when expressed in Xenopus laevis oocytes and Nicotiana benthamiana cells, Ma1 mediates a malate-dependent inward-rectifying current, whereas the ma1-mediated transmembrane current is much weaker, indicating that ma1 has significantly lower malate transport activity than Ma1. RNA interference suppression of Ma1 expression in 'McIntosh' apple leaves, 'Empire' apple fruit, and 'Orin' apple calli results in a significant decrease in malate level. Genotyping and phenotyping of 186 apple accessions from a diverse genetic background of 17 Malus species combined with the functional analyses described above indicate that Ma1 plays a key role in determining fruit acidity and that the truncation of Ma1 to ma1 is genetically responsible for low fruit acidity in apple. Furthermore, we identified a C-terminal domain conserved in all tonoplast-localized ALMTs essential for Ma1 function; protein truncations into this conserved domain significantly lower Ma1 transport activity. We conclude that the truncation of Ma1 to ma1 reduces its malate transport function by removing a conserved C-terminal domain, leading to low fruit acidity in apple.

中文翻译：

Apple ALMT9 需要一个保守的 C 末端结构域来传输果酸的苹果酸。

液泡中苹果酸的积累很大程度上决定了苹果 (Malus Domestica) 果实的酸度，而低果实酸度与 Ma1 的截短密切相关，Ma1 是拟南芥 (Arabidopsis thaliana) 中铝激活苹果酸转运蛋白 9 (ALMT9) 的直系同源物。 Ma1 开放阅读框中第 1,455 位碱基的突变导致提前终止密码子，从而在 C 末端截断蛋白质 84 个氨基酸。在这里，我们报告全长蛋白 Ma1 及其天然存在的截短蛋白 ma1 都定位于液泡膜；当在非洲爪蟾卵母细胞和本塞姆氏烟草细胞中表达时，Ma1介导苹果酸依赖性内向整流电流，而ma1介导的跨膜电流要弱得多，表明ma1的苹果酸转运活性显着低于Ma1。 RNA 干扰抑制“McIntosh”苹果叶、“Empire”苹果果实和“Orin”苹果愈伤组织中 Ma1 的表达，导致苹果酸水平显着下降。对来自 17 个苹果属物种的不同遗传背景的 186 个苹果种质进行基因分型和表型分析，结合上述功能分析表明，Ma1 在确定果实酸度中起着关键作用，并且 Ma1 截短为 ma1 在遗传上是导致苹果果酸度低的原因。苹果。此外，我们还发现了一个在所有液泡膜定位的 ALMT 中保守的 C 端结构域，该结构域对 Ma1 功能至关重要；将蛋白质截断到这个保守结构域会显着降低 Ma1 转运活性。我们得出的结论是，Ma1 截短为 ma1 通过去除保守的 C 末端结构域降低了其苹果酸转运功能，导致苹果的果实酸度较低。

更新日期：2020-01-31

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