Metabolomic homeostasis shifts after callus formation and shoot regeneration in tomato

Plants can regenerate from a variety of tissues on culturing in appropriate media. However, the metabolic shifts involved in callus formation and shoot regeneration are largely unknown. The metabolic profiles of callus generated from tomato (Solanum lycopersicum) cotyledons and that of shoot regenerated from callus were compared with the pct1-2 mutant that exhibits enhanced polar auxin transport and the shr mutant that exhibits elevated nitric oxide levels. The transformation from cotyledon to callus involved a major shift in metabolite profiles with denser metabolic networks in the callus. In contrast, the transformation from callus to shoot involved minor changes in the networks. The metabolic networks in pct1-2 and shr mutants were distinct from wild type and were rewired with shifts in endogenous hormones and metabolite interactions. The callus formation was accompanied by a reduction in the levels of metabolites involved in cell wall lignification and cellular immunity. On the contrary, the levels of monoamines were upregulated in the callus and regenerated shoot. The callus formation and shoot regeneration were accompanied by an increase in salicylic acid in wild type and mutants. The transformation to the callus and also to the shoot downregulated LST8 and upregulated TOR transcript levels indicating a putative linkage between metabolic shift and TOR signalling pathway. The network analysis indicates that shift in metabolite profiles during callus formation and shoot regeneration is governed by a complex interaction between metabolites and endogenous hormones.

植物可在适宜培养基中通过多种组织实现再生。然而，愈伤组织（callus）形成与芽再生（shoot regeneration）过程中涉及的代谢重编程，目前大多尚未明确。本研究对番茄（Solanum lycopersicum）子叶来源的愈伤组织、愈伤组织再生芽的代谢谱，与生长素极性运输（polar auxin transport）增强的pct1-2突变体、一氧化氮（nitric oxide）水平升高的shr突变体的对应样品进行了比较分析。子叶向愈伤组织的转变伴随代谢谱的显著重编程，愈伤组织的代谢网络更为密集。与之相反，愈伤组织向芽的转变仅伴随代谢网络的小幅变化。pct1-2与shr突变体的代谢网络与野生型存在显著差异，且通过内源激素与代谢物互作的重编程得以重塑。愈伤组织形成过程中，参与细胞壁木质化与细胞免疫的代谢物水平显著下调。与之相反，愈伤组织与再生芽中的单胺类物质（monoamines）水平均显著上调。野生型与突变体在愈伤组织形成及芽再生过程中，水杨酸（salicylic acid）水平均有所升高。向愈伤组织及芽的转变过程中，LST8的转录水平下调，而TOR的转录水平上调，这表明代谢重编程与TOR信号通路之间存在潜在关联。网络分析结果表明，愈伤组织形成与芽再生过程中的代谢谱重编程，由代谢物与内源激素之间的复杂互作所调控。