Sucrose-Induced Transcription Factor IjSUSIBA2 Fine-Tunes Growth Transition Through the IjSVL2-IjFLCL1 Module in Evergreen Irises.

Sugar metabolism is commonly implicated as crucial in the transition between growth and cessation during winter; however, its exact role remains elusive. The evergreen iris (Iris japonica) ceases growth in winter without entering endodormancy, yet it continues to sustain sugar metabolism and transport throughout the season. Here, we elucidate the mechanisms underlying the sugar-mediated growth transition-the shift between growth and cessation-in I. japonica through integrative physiological and transcriptional analyses. We investigated the function and transcriptional regulation of FLOWERING LOCUS C-LIKE 1 (IjFLCL1) and demonstrated that IjFLCL1 promotes growth resumption. Additionally, ALPHA-AMYLASE-LIKE 3 (IjAMY3), a starch degradation gene downstream of IjFLCL1, inhibits growth in I. japonica, potentially by modulating endogenous starch granule dynamics. Moreover, sugar-induced transcription factor SUGAR SIGNALING IN BARLEY 2 (IjSUSIBA2) activates IjFLCL1 expression. Conversely, IjSUSIBA2 directly represses the well-known dormancy mediator SHORT VEGETATIVE PHASE-LIKE 2 (IjSVL2), which in turn inhibits IjFLCL1 expression. IjSUSIBA2 may be induced by both exogenous and endogenous sugar signals, subsequently regulating downstream genes. Overall, our results suggest sugar molecules might serve as both signals and energy to regulate growth transition through IjFLCL1-mediated novel pathways. These insights carry valuable implications for the cultivation and breeding of perennials to withstand the challenges posed by climate change.