From Floral Induction to Blooming: The Molecular Mysteries of Flowering in Woody Plants

Abstract

Flowering is a pivotal developmental process in response to the environment and determines the start of a new life cycle in plants. Woody plants usually possess a long juvenile nonflowering phase followed by an adult phase with repeated flowering cycles. The molecular mechanism underlying flowering regulation in woody plants is believed to be much more complex than that in annual herbs. In this review, we briefly describe the successive but distinct flowering processes in perennial trees, namely the vegetative phase change, the floral transition, floral organogenesis, and final blooming, and summarize in detail the most recent advances in understanding how woody plants regulate flowering through dynamic gene expression. Notably, the florigen gene FLOWERING LOCUS T(FT) and its antagonistic gene TERMINAL FLOWER 1 (TFL1) seem to play a central role in various flowering transition events. Flower development in different taxa requires interactions between floral homeotic genes together with AGL6 conferring floral organ identity. Finally, we illustrate the issues and corresponding measures of flowering regulation investigation. It is of great benefit to the future study of flowering in perennial trees.

Keywords: floral organogenesis; flowering; regulatory mechanism; woody plants.

Figure 1

Schematic presentation of flowering phenology in woody trees. The juvenile-to-adult vegetative transition refers to a long period before woody trees first acquire flowering ability; the vegetative-to-reproductive transition commonly shows repeated cycling or rather seasonal periodicity, indicating flower formation follows the floral transition; “Direct flowering” refers to trees that finish their complete reproductive cycle during a single growing season without a dormancy period, while “indirect flowering” means the trees undergo winter dormancy before final blooming.

Figure 2

Diagram illustrating the molecular model underlying flowering regulation in perennial trees, which incorporates important/central genes and microRNAs as well as epigenetic modification. Black solid arrows indicate gene regulation; green dotted arrows indicate epigenetic modification participating in gene regulatory modules; brown dotted arrows represent responses to environmental cues.