Solanum tuberosum potato lines with high amylose content were generated by crossing with the wild potato species Solanum sandemanii followed by repeated backcrossing to Solanum tuberosum lines. The trait, termed increased amylose (IAm), was recessive and present after three generations of backcrossing into S. tuberosum lines (6.25% S. sandemanii genes). The tubers of these lines were small, elongated and irregular with small and misshaped starch granules and high sugar content. Additional backcrossing resulted in less irregular tuber morphology, increased starch content (4.3%–9.5%) and increased amylose content (29%–37.9%) but indifferent sugar content. The amylose in the IAm starch granules was mainly located in peripheral spots, and large cavities were found in the granules. Starch pasting was suppressed, and the digestion‐resistant starch (RS) content was increased. Comprehensive microarray polymer profiling (CoMPP) analysis revealed specific alterations of major pectic and glycoprotein cell wall components. This complex phenotype led us to search for candidate IAm genes exploiting its recessive trait. Hence, we sequenced genomic DNA of a pool of IAm lines, identified SNPs genome wide against the draft genome sequence of potato and searched for regions of decreased heterozygosity. Three regions, located on chromosomes 3, 7 and 10, respectively, displayed markedly less heterozygosity than average. The only credible starch metabolism‐related gene found in these regions encoded the isoamylase‐type debranching enzyme Stisa1. Decreased expression of mRNA (>500 fold) and reduced enzyme activity (virtually absent from IAm lines) supported Stisa1 as a candidate gene for IAm.

中文翻译：

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非转基因马铃薯品系合成的直链淀粉和抗性淀粉增加，主要缺乏异淀粉酶脱支酶

通过与野生马铃薯品种Solanum sandemanii杂交，然后与马铃薯品系反复回交，产生了具有高直链淀粉含量的马铃薯品系。该性状称为直链淀粉增加 (IAm)，是隐性的，在与马铃薯品系（6.25% S. sandemanii基因）回交三代后出现。这些品系的块茎小、拉长且不规则，淀粉粒小且形状不规则，含糖量高。额外的回交导致块茎形态不规则性减少，淀粉含量增加（4.3%–9.5%），直链淀粉含量增加（29%–37.9%），但糖含量无差异。IAm淀粉颗粒中的直链淀粉主要位于外围斑点，颗粒中存在较大的空洞。淀粉糊化受到抑制，抗消化淀粉（RS）含量增加。综合微阵列聚合物分析（CoMPP）分析揭示了主要果胶和糖蛋白细胞壁成分的特定变化。这种复杂的表型促使我们利用其隐性特征来寻找候选 IAm 基因。因此，我们对一组 IAm 品系的基因组 DNA 进行了测序，根据马铃薯基因组草图序列鉴定了全基因组 SNP，并寻找杂合性降低的区域。分别位于 3、7 和 10 号染色体上的三个区域的杂合性明显低于平均水平。在这些区域中发现的唯一可信的淀粉代谢相关基因编码异淀粉酶型脱支酶 Stisa1。mRNA 表达降低（>500 倍）和酶活性降低（IAm 系中几乎不存在）支持Stisa1作为 IAm 的候选基因。