A natural mutation-led truncation in one of the two aluminum-activated malate transporter-like genes at the Ma locus is associated with low fruit acidity in apple
A natural mutation-led truncation in one of the two aluminum-activated malate transporter-like genes at the Ma locus is associated with low fruit acidity in apple
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DOI：
10.1007/s00438-012-0707-7
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发表时间：
2012-08-01
影响因子：
3.1
通讯作者：
Xu, Kenong
中科院分区：
文献类型：
--
作者：
Bai, Yang;Dougherty, Laura;Xu, Kenong
酸度水平极大地影响水果的味道和风味，从而影响其市场价值。在成熟的苹果果实中，苹果酸是主要的有机酸。一些研究已经证实，主要数量性状位点Ma在很大程度上控制了果实酸度水平的变化。最近已被定义在一个150 kb的区域，包含44个预测的基因在16号染色体上的金冠基因组中的马位点。在这项研究中，我们确定了两个铝激活的苹果酸转运蛋白样基因，命名为Ma 1和Ma 2，作为马的强有力的候选人，通过缩小马位点到65-82 kb，包含12-19个预测的基因取决于单倍型。通过对来自G.41（基因型Mama的苹果砧木）的两个细菌人工染色体克隆进行测序来确定Ma单倍型，所述克隆覆盖Ma基因座处的两个不同单倍型。对18份苹果种质的基因表达谱分析表明，Ma 1是控制苹果酸度的主要基因，Ma 1的表达量远高于Ma 2，且Ma 1的表达量与苹果可滴定酸度呈显著正相关（R（2）= 0.4543，P = 0.0021）。在Ma 1和Ma 2的低酸度等位基因编码序列中，未检测到金冠与G.41之间在氨基酸水平上的序列变异。但高酸度的等位基因在两种基因型之间差异很大。Ma 1的低酸度等位基因Ma 1 - 1455 A的主要特征是开放阅读框中第1455位碱基的突变。该突变导致一个提前终止密码子，与Ma 1 - 1455 G相比，Ma 1 - 1455 A的羧基末端被截短了84个氨基酸。利用标记CAPS（1455）对29份苹果种质资源进行的调查表明，CAPS（1455 A）等位基因与高pH值完全相关，与低可滴定酸度高度相关，这表明自然突变导致的截短很可能是导致苹果中Ma对低pH或高酸度功能丧失的原因。
Acidity levels greatly affect the taste and flavor of fruit, and consequently its market value. In mature apple fruit, malic acid is the predominant organic acid. Several studies have confirmed that the major quantitative trait locus Ma largely controls the variation of fruit acidity levels. The Ma locus has recently been defined in a region of 150 kb that contains 44 predicted genes on chromosome 16 in the Golden Delicious genome. In this study, we identified two aluminum-activated malate transporter-like genes, designated Ma1 and Ma2, as strong candidates of Ma by narrowing down the Ma locus to 65-82 kb containing 12-19 predicted genes depending on the haplotypes. The Ma haplotypes were determined by sequencing two bacterial artificial chromosome clones from G.41 (an apple rootstock of genotype Mama) that cover the two distinct haplotypes at the Ma locus. Gene expression profiling in 18 apple germplasm accessions suggested that Ma1 is the major determinant at the Ma locus controlling fruit acidity as Ma1 is expressed at a much higher level than Ma2 and the Ma1 expression is significantly correlated with fruit titratable acidity (R (2) = 0.4543, P = 0.0021). In the coding sequences of low acidity alleles of Ma1 and Ma2, sequence variations at the amino acid level between Golden Delicious and G.41 were not detected. But the alleles for high acidity vary considerably between the two genotypes. The low acidity allele of Ma1, Ma1-1455A, is mainly characterized by a mutation at base 1455 in the open reading frame. The mutation leads to a premature stop codon that truncates the carboxyl terminus of Ma1-1455A by 84 amino acids compared with Ma1-1455G. A survey of 29 apple germplasm accessions using marker CAPS(1455) that targets the SNP1455 in Ma1 showed that the CAPS(1455A) allele was associated completely with high pH and highly with low titratable acidity, suggesting that the natural mutation-led truncation is most likely responsible for the abolished function of Ma for low pH or high acidity in apple.