Effect ofphyBandphyCloss-of-function mutations on the wheat transcriptome under short and long day photoperiods

Abstract

25Background: Photoperiod signals provide important cues by which plants regulate their growth 26 and development in response to predictable seasonal changes. Phytochromes, a family of red and 27 far-red light receptors, play critical roles in regulating flowering time in response to changing 28 photoperiods. A previous study showed that loss-of-function mutations in either PHYB or PHYC 29 result in large delays in heading time and in the differential regulation of a large number of genes 30 in wheat plants grown in an inductive long day (LD) photoperiod. 31 Results:We found that under non-inductive short-day (SD) photoperiods, phyB-null and phyC-32 null mutants were taller, had a reduced number of tillers, longer and wider leaves, and headed 33 later than wild-type plants. Unexpectedly, both mutants flowered earlier in SD than LD, the 34 inverse response to that of wild-type plants. We observed a larger number of differentially 35 expressed genes between mutants and wild-type under SD than under LD, and in both cases, the 36 number was larger for phyB than for phyC. We identified subsets of differentially expressed and 37 alternatively spliced genes that were specifically regulated by PHYB and PHYC in either SD or 38 LD photoperiods, and a smaller set of genes that were regulated in both photoperiods. We 39 observed significantly higher transcript levels of the flowering promoting genes VRN-A1, PPD-40 B1 and GIGANTEA in the phy-null mutants in SD than in LD, which suggests that they could 41 contribute to the earlier flowering of the phy-null mutants in SD than in LD. 42 Conclusions: Our study revealed an unexpected reversion of the wheat LD plants into SD plants 43in the phyB-null and phyC-null mutants and identified candidate genes potentially involved in 44 this phenomenon. Our RNA-seq data provides insight into light signaling pathways in inductive 45 and non-inductive photoperiods and a set of candidate genes to dissect the underlying 46 developmental regulatory networks in wheat. 47 Keywords: Wheat, heading date, phytochrome, FT1, FT2, FT3, PPD1, VRN1. 48 Background 49As sessile organisms, plants must be able to respond to fluctuations in their environment to 50 maximize their reproductive success. To achieve this, plants have evolved a series of regulatory 51 mechanisms to ensure that critical stages of their development coincide with optimal 52 environmental conditions. One important determinant of reproductive success is flowering time, 53 which is strongly influenced by seasonal changes in photoperiod and temperature [1]. In cereal 54 crops, these cues are fundamental to ensure the plant does not flower too early, to prevent 55 exposure of sensitive reproductive tissues to late-spring frosts, or too late, so as to minimize 56 exposure to damaging high temperatures during grain filling [2]. There is a direct link between 57 reproductive success and grain production, so characterizing the regulatory networks underlying 58 flowering time is critical to support the development of resilient crop varieties, ...

Epistatic interactions betweenPHOTOPERIOD-1, CONSTANS 1andCONSTANS 2modulate the photoperiodic response in wheat

“…The upregulation of VRN1 in the ppd1 mutant under SD ( Fig 5E) suggests the possibility that PPD1 may be involved in this SD repression mechanism. A strong SD upregulation of VRN1 has also been reported in phyC and phyB mutants of Kronos-PI, which also showed a significant down-regulation of PPD1 [32].…”

“…Since phytochromes PHYC [15] and PHYB [31] are both required for the LD transcriptional activation of PPD1, we explored the effect of mutations in these two phytochromes on the expression profiles of CO1 and CO2. To do this, we used recently published RNAseq studies for leaf samples (4 th leaf, ZT 4h) from loss-of-function mutants phyB and phyC in Kronos-PI under both LD [31] and SD conditions [32].…”

Light spectra trigger divergent gene expression in barley cultivars

“…Both PhyC and PhyB are required for the photoperiodic induction of flowering in wheat (Pearce et al ., 2016; Kippes et al ., 2020). Null wheat mutants of either PhyC or PhyB produced late-flowering plants, with altered vegetative development.…”

“…The connection between photoreceptor and photoperiod pathways has been attributed to PhyC, which activates the long-day photoperiod response gene, PPD-1 in LD (Nishida et al ., 2013; Chen et al ., 2014; Pankin et al ., 2014; Woods et al ., 2014). Both PhyC and PhyB promote flowering under LD, although PhyB regulates more genes than PhyC (Kippes et al ., 2020), particularly those involved in vegetative development, hormone biosynthesis, and signaling, shade avoidance response, abiotic stress tolerance (Pearce et al ., 2016), and cold tolerance (Franklin and Quail, 2010; Novák et al ., 2016).…”