Temperature-Regulated Flowering Locus T Like gene Coordinates the Spike Initiation in Phalaenopsis orchid.

Phalaenopsis aphrodite can be induced to initiate spike growth and flowering by exposure to low ambient temperatures. However, the factors and mechanisms responsible for spike initiation in P. aphrodite remain largely unknown. In this study, we show that a repressor FLOWERING LOCUS T-like gene, FTL, can act as a negative regulator of spike initiation in P. aphrodite. The mRNA transcripts of PaFTL are consistently high during high ambient temperature, thereby preventing premature spike initiation. However, during low ambient temperature, PaFTL expression falls while FLOWERING LOCUS T (FT) expression increases, allowing for spike initiation. Knock-down of PaFTL expression through virus-inducing gene silencing (VIGS) promoted spike initiation at 30/28°C. Moreover, PaFTL interacts with FLOWERING LOCUS D (FD) in a similar manner to FT, to regulate downstream flowering initiation genes. Transgenic P. aphrodite plants exhibiting high expression of PaFTL do not undergo spike initiation, even when exposed to low ambient temperatures. These findings shed light on the flowering mechanisms in Phalaenopsis and provide new insights into how perennial plants govern spike initiation in response to temperature cues.