AtMYB2Regulates Whole Plant Senescence by Inhibiting Cytokinin-Mediated Branching at Late Stages of Development in Arabidopsis

Yongfeng Guo,Susheng Gan

doi:10.1104/pp.111.177022

Abstract

Whole plant senescence of monocarpic plants consists of three major processes: arrest of shoot apical meristem, organ senescence, and permanent suppression of axillary buds. At early stages of development, axillary buds are inhibited by shoot apex-produced auxin, a mechanism known as apical dominance. How the buds are suppressed as an essential part of whole plant senescence, especially when the shoot apexes are senescent, is not clear. Here, we report an AtMYB2-regulated post apical dominance mechanism by which Arabidopsis (Arabidopsis thaliana) inhibits the outgrowth of axillary buds as part of the whole plant senescence program. AtMYB2 is expressed in the compressed basal internode region of Arabidopsis at late stages of development to suppress the production of cytokinins, the group of hormones that are required for axillary bud outgrowth. atmyb2 T-DNA insertion lines have enhanced expression of cytokinin-synthesizing isopentenyltransferases genes, contain higher levels of cytokinins, and display a bushy phenotype at late stages of development. As a result of the continuous generation of new shoots, atmyb2 plants have a prolonged life span. The AtMYB2 promoter-directed cytokinin oxidase 1 gene in the T-DNA insertion lines reduces the endogenous cytokinin levels and restores the bushy phenotype to the wild type.

Highlights

Whole plant senescence of monocarpic plants consists of three major processes: arrest of shoot apical meristem, organ senescence, and permanent suppression of axillary buds
RNA gelblot and reverse transcription (RT)-PCR analyses confirmed the high expression of this gene during leaf senescence (Supplemental Fig. S1)
The T-DNA was inserted in the third exon of AtMYB2 (Fig. 1C) and resulted in no detectable AtMYB2 transcript (Fig. 1D; Supplemental Fig. S2)

Summary

Introduction

Whole plant senescence of monocarpic plants consists of three major processes: arrest of shoot apical meristem, organ senescence, and permanent suppression of axillary buds. At early stages of development, axillary buds are inhibited by shoot apex-produced auxin, a mechanism known as apical dominance. We report an AtMYB2-regulated post apical dominance mechanism by which Arabidopsis (Arabidopsis thaliana) inhibits the outgrowth of axillary buds as part of the whole plant senescence program. AtMYB2 is expressed in the compressed basal internode region of Arabidopsis at late stages of development to suppress the production of cytokinins, the group of hormones that are required for axillary bud outgrowth. The axillary buds are generally suppressed by shoot apex-produced auxin, a mechanism known as apical dominance (Thimann and Skoog, 1933; Napoli et al, 1999). IPT catalyzes the first and rate-limiting step in the biosynthesis of cytokinins This suggests that auxin could act by reducing the supply of cytokinins to axillary buds, thereby inhibiting their growth. It has been suggested that strigolactone may function by repressing the cytokinin pathway (Dun et al, 2009)

Methods

Results

Conclusion