Effect of phyB and phyC loss-of-function mutations on the wheat transcriptome under short and long day photoperiods

Nestor Kippes,Carl Vangessel,Hikmet Budak,James Hamilton,Jorge Dubcovsky,Ani Akpinar,Stephen Pearce

doi:10.1186/s12870-020-02506-0

Abstract

BackgroundPhotoperiod signals provide important cues by which plants regulate their growth and development in response to predictable seasonal changes. Phytochromes, a family of red and far-red light receptors, play critical roles in regulating flowering time in response to changing photoperiods. A previous study showed that loss-of-function mutations in either PHYB or PHYC result in large delays in heading time and in the differential regulation of a large number of genes in wheat plants grown in an inductive long day (LD) photoperiod.ResultsWe found that under non-inductive short-day (SD) photoperiods, phyB-null and phyC-null mutants were taller, had a reduced number of tillers, longer and wider leaves, and headed later than wild-type (WT) plants. The delay in heading between WT and phy mutants was greater in LD than in SD, confirming the importance of PHYB and PHYC in accelerating heading date in LDs. Both mutants flowered earlier in SD than LD, the inverse response to that of WT plants. In both SD and LD photoperiods, PHYB regulated more genes than PHYC. We identified subsets of differentially expressed and alternatively spliced genes that were specifically regulated by PHYB and PHYC in either SD or LD photoperiods, and a smaller set of genes that were regulated in both photoperiods. We found that photoperiod had a contrasting effect on transcript levels of the flowering promoting genes VRN-A1 and PPD-B1 in phyB and phyC mutants compared to the WT.ConclusionsOur study confirms the major role of both PHYB and PHYC in flowering promotion in LD conditions. Transcriptome characterization revealed an unexpected reversion of the wheat LD plants into SD plants in the phyB-null and phyC-null mutants and identified flowering genes showing significant interactions between phytochromes and photoperiod that may be involved in this phenomenon. Our RNA-seq data provides insight into light signaling pathways in inductive and non-inductive photoperiods and a set of candidate genes to dissect the underlying developmental regulatory networks in wheat.

Highlights

Photoperiod signals provide important cues by which plants regulate their growth and development in response to predictable seasonal changes
We identified several other members of the Phosphatidylethanolamine-Binding Protein (PEBP) family that were upregulated in long day (LD) conditions (Additional file 5), for which it would be interesting to characterize their role in wheat heading date
The characterization of loss-of-function mutants for PHYTOCHROME B (PHYB) and PHYC in tetraploid wheat revealed that these genes regulate both vegetative development and heading time, with larger differences between the phy-null mutants and the WT under LD than under SD

Summary

Introduction

Photoperiod signals provide important cues by which plants regulate their growth and development in response to predictable seasonal changes. One important determinant of reproductive success is flowering time, which is strongly influenced by seasonal changes in photoperiod and temperature [1]. In cereal crops, these cues are fundamental to ensure the plant does not flower too early, to prevent exposure of sensitive reproductive tissues to late-spring frosts, or too late, so as to minimize exposure to damaging high temperatures during grain filling [2]. The temperate cereals, including common wheat (Triticum aestivum L.), are LD plants This ensures that plants remain in a vegetative phase during winter until the lengthening days of spring trigger the irreversible transition to reproductive development [1]. An additional requirement for a long period at low temperatures (vernalization) prevents flowering during the fall, when the days are still relatively long [3]

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