Nitrogen fertilization plays a key role in the accumulation of soluble sugars and organic acids in blackberry (Rubus spp.). To understand the effects of different levels of nitrogen fertilization on the accumulation of soluble sugars and organic acids in floricane-fruiting blackberry cultivar ‘Shuo Feng’ ripe fruit and the underlying molecular mechanisms, a comprehensive analysis of physiological, metabolomic and transcriptomic data was carried out. The five nitrogen application levels for the blackberry plants were 0 g plant−1 (CK), 20 g plant−1 (T1), 40 g plant−1 (T2), 60 g plant−1 (T3) and 80 g plant−1 (T4). The appropriate nitrogen application level (20–40 g plant−1) increased the accumulation of soluble sugars and decreased the content of organic acids in the fruit; the opposite was true under nitrogen deficiency (0 g plant−1) and excessive nitrogen application (80 g plant−1). Transcriptomic and metabolomic analyses of the CK, T2 and T4 treatments revealed candidate genes regulating soluble sugar and organic acid accumulation. Appropriate nitrogen fertilization upregulated the expression of sucrose synthase (SuS1, SuS2), endoglucanase (EGase1) and beta-glucosidase (BG4, BG5 and BG7) genes to increase soluble sugar accumulation and upregulated the expression of NAD-malate dehydrogenase (NAD-ME) and NADP-dependent malic enzyme (NADP-ME) genes to increase organic acid catabolism. While nitrogen deficiency and excessive nitrogen application upregulated the expression of sucrose-phosphate synthase (SPS1) and alpha-amylase (AMY1, AMY2) genes, as well as AP2/ERF, WRKY, bHLH and MYB1 transcription factors, to increase starch catabolism and inhibit organic acid degradation, which improved blackberry resistance to nitrogen stress. This study provides an accurate scientific basis for promoting the effective accumulation of sugars in blackberry fruit via fertilization.

中文翻译：

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不同施氮水平对黑莓果实可溶性糖和有机酸积累影响的转录组学和代谢组学联合分析


氮肥在黑莓 （Rubus spp.） 中可溶性糖和有机酸的积累中起着关键作用。为了解不同施氮水平对花果黑莓品种'硕丰'成熟果实可溶性糖和有机酸积累的影响及其分子机制，对生理学、代谢组学和转录组学数据进行了综合分析。黑莓植株的 5 个施氮水平分别为 0 g 植株−1 （CK）、20 g 植株−1 （T1）、40 g 植株−1 （T2）、60 g 植株−1 （T3） 和 80 g 植株−1 （T4）。适当的氮肥施用水平（20-40 g 植物-1）增加了果实中可溶性糖的积累并降低了有机酸的含量;在缺氮 （0 g 植物-1） 和过量施氮 （80 g 植物-1） 下，情况正好相反。CK 、 T2 和 T4 处理的转录组学和代谢组学分析揭示了调节可溶性糖和有机酸积累的候选基因。适当的氮肥上调蔗糖合酶 （SuS1， SuS2） 、内切葡聚糖酶 （EGase1） 和 β-葡萄糖苷酶 （BG4， BG5 和 BG7） 基因的表达，增加可溶性糖积累，上调 NAD-苹果酸脱氢酶 （NAD-ME） 和 NADP 依赖性苹果酸酶 （NADP-ME） 基因的表达，增加有机酸分解代谢。而缺氮和过量施氮上调蔗糖磷酸合酶 （SPS1） 和 α-淀粉酶 （AMY1， AMY2） 基因的表达，以及 AP2/ERF、WRKY、bHLH 和 MYB1 转录因子的表达，增加淀粉分解代谢并抑制有机酸降解，从而提高黑莓对氮胁迫的抵抗力。 本研究为通过施肥促进黑莓果实中糖分的有效积累提供了准确的科学依据。