Fruit firmness is an important trait for characterizing the quality and value of apple. It is also serves as an indicator of fruit maturity, as it is a complex trait regulated by multiple genes. Re-sequencing techniques can be employed to elucidate variations in such complex fruit traits. Here, the whole genomes of 294 F1 hybrids of ‘Fuji’ and ‘Cripp's Pink’ were re-sequenced, and a high-density bin-map was constructed using 5,014 bin markers with a total map distance of 2,213.23 cM and an average map distance of 0.44 cM. Quantitative trait loci (QTLs) of traits related to fruit were mapped, and an A-T allele variant identified in the coding region of MdNAC5 was found to potentially regulate fruit firmness and ripening. The overexpression of MdNAC5A resulted in higher production of methionine and 1-aminocyclopropanecarboxylic acid compared to MdNAC5T, leading to reduced fruit firmness and accelerated ripening in apples and tomatoes. Furthermore, the activities of MdNAC5A and MdNAC5T were enhanced through their differential binding to the promoter regions of MdACS1 and MdERF3. Spatial variations in MdNAC5A and MdNAC5T caused changes in MdACS1 expression following their interaction with MdERF3. Ultimately, utilizing different MdNAC5 alleles offers a strategy to manipulate fruit firmness in apple breeding.

中文翻译：

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MdNAC5 的自然变化有助于苹果果实的硬度和成熟分化


果实硬度是表征苹果品质和价值的重要特征。它也可以作为水果成熟的指标，因为它是由多个基因调节的复杂性状。可以采用重测序技术来阐明这种复杂水果性状的变化。在这里，对 'Fuji' 和 'Cripp's Pink' 的 294 个 F1 杂交种的全基因组进行了重新测序，并使用 5,014 个 bin 标记构建了高密度 bin-map，总图距为 2,213.23 cM，平均图距为 0.44 cM。绘制与果实相关性状的数量性状位点 （QTL），发现在 MdNAC5 编码区鉴定的 A-T 等位基因变体可能调节果实的硬度和成熟度。与 MdNAC5T 相比，MdNAC5A 的过表达导致蛋氨酸和 1-氨基环丙烷羧酸的产生增加，导致苹果和西红柿的果实硬度降低并加速成熟。此外，MdNAC5A 和 MdNAC5T 的活性通过与 MdACS1 和 MdERF3 的启动子区域的差异结合而增强。MdNAC5A 和 MdNAC5T 的空间变化导致 MdACS1 表达在与 MdERF3 相互作用后发生变化。最终，利用不同的 MdNAC5 等位基因提供了一种在苹果育种中操纵果实硬度的策略。