Citrus is one of the most important fruit crop genera in the world, but many Citrus species are vulnerable to cold stress. Ichang papeda (Citrus ichangensis), a cold-hardy citrus species, holds great potential for identifying valuable metabolites that are critical for cold tolerance in Citrus. However, the metabolic changes and underlying mechanisms that regulate Ichang papeda cold tolerance remain largely unknown. In this study, we compared the metabolomes and transcriptomes of Ichang papeda and HB pummelo (Citrus grandis ‘Hirado Buntan’, a cold-sensitive species) to explore the critical metabolites and genes responsible for cold tolerance. Metabolomic analyses led to the identification of common and genotype-specific metabolites, consistent with transcriptomic alterations. Compared to HB pummelo under cold stress, Ichang papeda accumulated more sugars, flavonoids, and unsaturated fatty acids, which are well-characterized metabolites involved in stress responses. Interestingly, sphingosine and chlorogenic acid substantially accumulated only in Ichang papeda. Knockdown of CiSPT (C. ichangensis serine palmitoyltransferase) and CiHCT2 (C. ichangensis hydroxycinnamoyl-CoA: shikimate hydroxycinnamoyltransferase2), two genes involved in sphingosine and chlorogenic acid biosynthesis, dramatically decreased endogenous sphingosine and chlorogenic acid levels, respectively. This reduction in sphingosine and chlorogenic acid notably compromised the cold tolerance of Ichang papeda, whereas exogenous application of these metabolites increased plant cold tolerance. Taken together, our findings indicate that greater accumulation of a spectrum of metabolites, particularly sphingosine and chlorogenic acid, promotes cold tolerance in cold-tolerant citrus species. These findings broaden our understanding of plant metabolic alterations in response to cold stress and provide valuable targets that can be manipulated to improve Citrus cold tolerance.

中文翻译：

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转录组和代谢组图谱揭示了鞘氨醇和绿原酸对柑橘耐冷性的贡献


柑橘是世界上最重要的水果作物属之一，但许多柑橘品种容易受到冷胁迫的影响。 Ichang papeda (Citrus ichangensis) 是一种耐寒柑橘品种，在鉴定对柑橘耐寒性至关重要的有价值的代谢物方面具有巨大潜力。然而，调节 Ichang papeda 耐寒性的代谢变化和潜在机制仍然很大程度上未知。在本研究中，我们比较了 Ichang papeda 和 HB pummelo（Citrus grandis 'Hirado Buntan'，一种冷敏感物种）的代谢组和转录组，以探索负责耐冷性的关键代谢物和基因。代谢组学分析导致​​了常见和基因型特异性代谢物的鉴定，与转录组学的改变一致。与冷胁迫下的HB柚相比，Ichang papeda积累了更多的糖、类黄酮和不饱和脂肪酸，这些都是参与应激反应的明确代谢物。有趣的是，鞘氨醇和绿原酸仅在Ichang papeda 中大量积累。 CiSPT（伊坎西斯丝氨酸棕榈酰转移酶）和 CiHCT2（伊坎西斯羟基肉桂酰辅酶 A：莽草酸羟基肉桂酰转移酶 2）这两个参与鞘氨醇和绿原酸生物合成的基因的敲除，分别显着降低了内源性鞘氨醇和绿原酸水平。鞘氨醇和绿原酸的减少显着损害了 Ichang papeda 的耐冷性，而外源施用这些代谢物则增强了植物的耐冷性。综上所述，我们的研究结果表明，一系列代谢物（特别是鞘氨醇和绿原酸）的更多积累可以促进耐冷柑橘品种的耐冷性。 这些发现拓宽了我们对植物响应冷胁迫的代谢变化的理解，并提供了可用于提高柑橘耐寒性的有价值的目标。