MiRNA Control of Vegetative Phase Change in Trees

Jia-Wei Wang,Detlef Weigel,R Scott Poethig,Xiao-Ya Chen,Mee Yeon Park,Yeonjong Koo,Ling-Jian Wang,Ronald R Sederoff

doi:10.1371/journal.pgen.1002012

Abstract

After germination, plants enter juvenile vegetative phase and then transition to an adult vegetative phase before producing reproductive structures. The character and timing of the juvenile-to-adult transition vary widely between species. In annual plants, this transition occurs soon after germination and usually involves relatively minor morphological changes, whereas in trees and other perennial woody plants it occurs after months or years and can involve major changes in shoot architecture. Whether this transition is controlled by the same mechanism in annual and perennial plants is unknown. In the annual forb Arabidopsis thaliana and in maize (Zea mays), vegetative phase change is controlled by the sequential activity of microRNAs miR156 and miR172. miR156 is highly abundant in seedlings and decreases during the juvenile-to-adult transition, while miR172 has an opposite expression pattern. We observed similar changes in the expression of these genes in woody species with highly differentiated, well-characterized juvenile and adult phases (Acacia confusa, Acacia colei, Eucalyptus globulus, Hedera helix, Quercus acutissima), as well as in the tree Populus x canadensis, where vegetative phase change is marked by relatively minor changes in leaf morphology and internode length. Overexpression of miR156 in transgenic P. x canadensis reduced the expression of miR156-targeted SPL genes and miR172, and it drastically prolonged the juvenile phase. Our results indicate that miR156 is an evolutionarily conserved regulator of vegetative phase change in both annual herbaceous plants and perennial trees.

Highlights

Plants produce different types of leaves, buds, and internodes at different times in their development
We show that the expression pattern of miR156—a master regulator of vegetative phase change in Arabidopsis and maize—is conserved in woody plants with well-defined juvenile and adult phases, and we show that over-expression of this microRNA prolongs the expression of the juvenile phase in the tree Populus x canadensis
Our results indicate that the mechanism of the juvenile-toadult transition is likely conserved throughout flowering plants

Summary

Introduction

Plants produce different types of leaves, buds, and internodes at different times in their development. Many traits vary continuously, other traits are expressed in discontinuous pattern that allows shoot development to be divided into discrete juvenile, adult, and reproductive phases [1,2,3,4,5]. These transitions involve changes in many different traits that must be temporally and spatially coordinated if the plant is to survive and reproduce. Juvenile leaves lack trichomes but possess epicuticular wax, whereas adult leaves have the opposite traits [4] These differences are mediated by two miRNAs, miR156 and miR172, both of which target DNA-binding transcription factors. Overexpression of the miR172-regulated genesTOE1 [13] and Glossy15 [15] delays the juvenile-to-adult vegetative transition

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Discussion

Conclusion