EARLY FLOWERING 3 and Photoperiod Sensing in Brachypodium distachyon.

Frédéric Bouché,Julie Linden,Daniel P Woods,Kevin S Mayer,Richard M Amasino,Claire Périlleux,Weiya Li

doi:10.3389/fpls.2021.769194

Abstract

The proper timing of flowering, which is key to maximize reproductive success and yield, relies in many plant species on the coordination between environmental cues and endogenous developmental programs. The perception of changes in day length is one of the most reliable cues of seasonal change, and this involves the interplay between the sensing of light signals and the circadian clock. Here, we describe a Brachypodium distachyon mutant allele of the evening complex protein EARLY FLOWERING 3 (ELF3). We show that the elf3 mutant flowers more rapidly than wild type plants in short days as well as under longer photoperiods but, in very long (20 h) days, flowering is equally rapid in elf3 and wild type. Furthermore, flowering in the elf3 mutant is still sensitive to vernalization, but not to ambient temperature changes. Molecular analyses revealed that the expression of a short-day marker gene is suppressed in elf3 grown in short days, and the expression patterns of clock genes and flowering time regulators are altered. We also explored the mechanisms of photoperiodic perception in temperate grasses by exposing B. distachyon plants grown under a 12 h photoperiod to a daily night break consisting of a mixture of red and far-red light. We showed that 2 h breaks are sufficient to accelerate flowering in B. distachyon under non-inductive photoperiods and that this acceleration of flowering is mediated by red light. Finally, we discuss advances and perspectives for research on the perception of photoperiod in temperate grasses.

Highlights

In many flowering plant species, photoperiod sensing is key to the synchronization of reproduction with seasonal changes in order to maximize reproductive success
Much is known about the many genes whose mutations affect flowering in Arabidopsis (Bouché et al, 2016), substantially fewer flowering control genes have been identified to date in temperate grasses, and many of these genes do not have homologs involved in flowering in Arabidopsis (Higgins et al, 2010; Ream et al, 2012)
EARLY FLOWERING 3 (ELF3) has been described as a key hub between photoperiodic signals and the circadian clock in both eudicots and monocots (Huang and Nusinow, 2016) and the results presented in this paper strongly support this interpretation and extend the characterization of the role of ELF3 to B. distachyon

Summary

INTRODUCTION

In many flowering plant species, photoperiod sensing is key to the synchronization of reproduction with seasonal changes in order to maximize reproductive success. In long-day flowering temperate grasses, the photoperiodmediated floral transition starts with the perception of light signals by phyB and phyC, which can form heterodimers (Nishida et al, 2013; Chen et al, 2014; Woods et al, 2014; Kippes et al, 2020) Active alleles of these two phytochromes are required for the induction of the pseudo-response regulator PHOTOPERIOD1 (PPD1) under LD (Chen et al, 2014; Pearce et al, 2016). We describe a new mutant allele of elf that was identified in a mutagenized population grown under short days (SD), highlighting that the role of ELF3 in circadian clock function and mediating the photoperiodic induction of flowering genes is conserved

MATERIALS AND METHODS

RESULTS

DISCUSSION AND PERSPECTIVES

DATA AVAILABILITY STATEMENT