The larch DAL1 interacts with PEBP family genes to regulate the annual growth cycle.

Boreal and temperate perennial woody plants coordinate annual growth cycle with seasonal environmental changes with age-dependent phenological differences. However, the underlying molecular mechanisms remain limited. In this study, we demonstrated that the MADS-box transcription factor DAL1 in Larix kaempferi (Japanese larch) directly regulates the expression of PEBP family genes LkFT1 and LkMFT to govern the annual growth cycle. LkDAL1 binds to the LkFT1 promoter to repress its expression, and to the LkMFT promoter to activate its expression. LkFT1 is highly expressed in the dormant stage, with its expression increased by short day and decreased by winter low temperature and subsequent spring warm temperature, whereas LkMFT is highly expressed in the active stage, with its expression decreased by short day. Notably, when it comes to tree age, LkFT1 is highly expressed in dormant young trees, LkMFT is highly expressed in active adult trees, and LkDAL1 expression levels increase with age in both dormant and active trees. Further, transient over-expression of LkFT1 in dormant larch delays bud break, that of LkMFT promotes bud break, and that of LkDAL1 promotes bud break; in addition, stable over-expression of LkDAL1 in poplar also promotes bud break. Moreover, over-expression of LkFT1 or LkMFT promotes flowering in Arabidopsis thaliana. Together, these findings uncover a novel mechanism in which the LkDAL1-PEBP module regulates the annual growth cycle in larch, providing new insights into age-dependent phenological differences in conifers.