Abstract
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.
Highlights
One distinctive character that distinguishes plants from animals is their remarkable capacity for regeneration
While pct1-2 and shr mutants differ from wild type (WT) in seedling phenotype, their cotyledons differ from WT primarily in size
Our study indicates that in the callus, and in regenerated shoot, other than zeatin and auxin that are present in culture media, the endogenous hormones play an important role in maintaining metabolomic homeostasis
Summary
One distinctive character that distinguishes plants from animals is their remarkable capacity for regeneration. The differentiated mature plant cells can undergo dedifferentiation followed by organogenesis and generation of fully fertile plant. Cells in the vicinity of the injury proliferate to form a mass of soft tissue consisting of pluripotent cells called as callus to seal the injured area. In vitro initiation of callus and organogenesis has been used for a plethora of biotechnological applications.
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