LAUSR

Abstract Lilium × formolongi, a facultative long-day (LD) plant, has precocious flowering characteristics, as it can flower within one year from seeds without the need for vernalization. Under normal LD conditions, the seedlings entered the flowering induction phase and bolted with 9−10 rosette leaves at 6 months after sowing. High temperature, especially at the root zone, inhibited bolting of the seedlings in LDs, accompanied by changes in plant shape and rapid expansion of underground bulbs. Low temperature in the natural environment could rapidly reverse the inhibition caused by high temperature, and promote bolting even under non-induced short days. The circadian clock and photoperiod pathways were disturbed at the transcriptional level by high temperature in both leaves and bulbs, such as LfCCA1, LfCRY, LfCOP1, LfFKF1, LfCOLs and LfPIFs. Thus, the flowering integrators LfFT1 and LfSOC1 were suppressed by high temperature. To determine the flowering inhibitors induced by high temperature in the root zone, the metabolome was analyzed under different conditions. ABA and ACC accumulation in the leaves and bulbs respectively during high temperature, was crucial to flowering inhibition possibly via interaction with the circadian clock and photoperiod-dependent pathways. Additionally, under high temperature conditions, D-allose, pentose and glucuronate interconversions and glutathione metabolism in the leaves were significantly activated. After cold exposure, TCA cycle was suppressed and SA, JA and some sugar (D-mannose, D-fructose, D-arabinose and maltotriose) levels were upregulated in the leaves, simultaneously with the vigorous fatty acid metabolism in the bulbs. These metabolic regulations were crucial to the phase transition under different conditions.