Abstract

DNA methylation controls many aspects of plant growth and development. Here, we report a novel annual growth potential change that may correlate with changes in levels of the major DNA demethylases and methyltransferases in cotton ovules harvested at different times of the year. The abundances of DNA demethylases, at both the mRNA and protein levels, increased significantly from February to August and decreased during the remainder of the 12-month period, with the opposite pattern observed for DNA methyltransferases. Over the course of one year, substantial changes in methylcytosine content was observed at certain CHH sites (H = A, C, or T) in the promoter regions of the ETHYLENE RESPONSIVE FACTOR 6 (ERF6), SUPPRESSION OF RVS 161 DELTA 4 (SUR4) and 3-KETOACYL-COA SYNTHASE 13 (KCS13), which regulate cotton fiber growth. Three independent techniques were used to confirm the annual fluctuations in DNA methylation. Furthermore, in homozygous RNAi lines specifically targeting REPRESSOR OF SILENCING 1 (ROS1, a conserved DNA demethylase domain), promotion of DNA methylation significantly reduced fiber growth during August.

Highlights

  • Most living organisms maintain an internal clock to estimate the passage of time and schedule physiological processes using a circadian clock of approximately 24 hours [1,2]

  • This shortterm time-keeping mechanism is precisely regulated by a network of transcriptional and posttranscriptional events [3,4], most of which involve the remodeling of chromatin through changes in histone acetylation [5,6,7]

  • In certain plants, increased dimethylation of lysine residue 9 and trimethylation of lysine 27 on histone H3 associated with the 59 regions of the FLOWERING LOCUS C (FLC) gene during the winter season may serve as an epigenetic memory system that represses FLC transcription and initiates flowering at the end of winter [9,10]

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Summary

Introduction

Most living organisms maintain an internal clock to estimate the passage of time and schedule physiological processes using a circadian clock of approximately 24 hours [1,2] This shortterm time-keeping mechanism is precisely regulated by a network of transcriptional and posttranscriptional events [3,4], most of which involve the remodeling of chromatin through changes in histone acetylation [5,6,7]. In certain plants, increased dimethylation of lysine residue 9 and trimethylation of lysine 27 on histone H3 associated with the 59 regions of the FLOWERING LOCUS C (FLC) gene during the winter season may serve as an epigenetic memory system that represses FLC transcription and initiates flowering at the end of winter [9,10] This ‘‘histone code’’, which specifies a silent chromatin state, appears to be conserved between animals and plants [5,6,10]. We constructed a large cDNA microarray containing all universal expressed sequence tags (UniESTs) obtained from sequencing of the upland cotton transcriptome, and used this to profile mRNA samples prepared from ovules harvested at different times of the year

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