PeTB1/2 and PeSLR1 mediate the mechanism of PePIN1b involved in axillary bud dormancy in Phalaenopsis

The complex architecture of plants, which has a profound impact on their productivity, is shaped by multiple factors, among which branching patterns play an important role. Phalaenopsis, with its exquisite floral beauty and abundant blooms, heavily depends on axillary buds for the development of its blossoms. This study involved the decapitation of Phalaenopsis, followed by a 14-day phase during which axillary buds at various developmental stages—pre-dormancy (S0), dormancy (S1), and dormancy release (S2)—selected for microscopic observation and RNA sequencing. The research revealed PeTB1 and PeTB2, members of the TCP class II CYC/TB1 clade, as a key regulator of axillary bud dormancy. The functional validation of these genes, achieved through Virus-Induced Gene Silencing (VIGS), highlighted their essential and overlapping roles in the dormancy process. Intriguingly, during the dormancy release phase, a decrease in auxin levels within the axillary buds was observed, which could be attributed to the auxin efflux transporter PePIN1b. Furthermore, the application of exogenous gibberellic acid (GA) expedited dormancy release, and transcriptome analysis identified PeSLR1, a key DELLA protein gene in the GA signaling pathway, as a key player. The silencing of PeSLR1 induced premature dormancy release in the axillary buds, reinforcing its regulatory importance. Notably, PeTB1, PeTB2, and PeSLR1 demonstrated complex interactions both in vivo and in vitro. Particularly, PeTB1 and PeTB2 suppressed the expression of PePIN1b, an auxin transporter gene, and PeSLR1 amplified this inhibitory effect of PeTB1. The mechanism of axillary bud dormancy in Phalaenopsis offers a theoretical basis for enhancing traits in Phalaenopsis production.