FLOWERING LOCUS T3 Controls Spikelet Initiation But Not Floral Development

Abstract

In many angiosperm plants, ()-like genes have duplicated and functionally diverged to control different reproductive traits or stages. Barley () carries several -like genes, the functions of which are not well understood. We characterized the role of HvFT3 in the vegetative and reproductive development of barley. Overexpression of accelerated the initiation of spikelet primordia and the early reproductive development of spring barley independently of the photoperiod. However, overexpression did not accelerate floral development, and inflorescences aborted under short days, suggesting that HvFT3 controls spikelet initiation but not floral development. Analysis of a nonfunctional allele supported the specific effects of this gene on spikelet initiation independent of the photoperiod. HvFT3 caused the up-regulation of the winter and spring alleles of the vernalization gene () in nonvernalized plants and was therefore dominant over the repressive effects of the vernalization pathway. Global transcriptome analysis in developing main shoot apices of the transgenic lines showed that HvFT3 modified the expression of genes involved in hormone synthesis and response, of floral homeotic genes, and of barley row-type genes (), (), and Understanding the specific functions of individual-like genes will allow modification of individual phases of preanthesis development and thereby adaptation to different environments and improved yield.

FLOWERING LOCUS T4 (HvFT4)delays flowering and decreases floret fertility in barley

“…Generation of transgenic Ubi::HvFT4 lines 106 Transgenic Ubi::HvFT4 lines were generated as described for Ubi::HvCO1 (Campoli et al,107 2012a), Ubi::HvCO2 (Mulki et al, 2016) and Ubi::HvFT3 (Mulki et al, 2018). The HvFT4 108 fragment was cloned from cDNA (cv.…”

“…Hd3a is induced 60 under inductive short day (SD) conditions to promote flowering, in contrast to its closest 61 homolog RFT1 which acts as major floral activator under LD conditions (Kojima et al, 2002;62 Hayama et al, 2003, Tamaki et al, 2007Komiya et al, 2008). Similarly, in barley FT1 and 63 FT2 are expressed under LDs and promote floral development, while FT3 is expressed under 64 SDs and LDs and induces spikelet initiation (Digel et al, 2015;Mulki et al, 2018;Shaw et al, 65 2019). However, the multifaceted roles of FT-like genes after extensive gene duplication events 66 within most flowering species is not yet described.…”

“…of Ppd-H1 that is associated with a decreased HvFT1 expression level under LD conditions 85 and a delay in flowering (Turner et al, 2005;Hemming et al, 2008). While HvFT1 is only 86 expressed and induces flowering under LD conditions, the homolog HvFT3 is expressed and 87 promotes reproductive development under long and short-day conditions (Mulki et al, 2018). 88 Experiments in wheat, barley, Brachypodium and rice suggested that FT2 is a floral promoter, 89 downstream of FT1 and expressed in the leaf as well as in the inflorescence (Kikuchi et al, 90 2009;Lv et al, 2014;Digel et al, 2015;Shaw et al, 2019).…”

“…Overexpression of HvFT4 prolonged vegetative growth and delayed 343 spikelet initiation. The effects of HvFT4 were antagonistic to those of HvFT1, HvFT2 and 344HvFT3, which promote spikelet initiation and inflorescence development in barley(Digel et 345 al., 2015, Mulki et al, 2018Shaw et al 2019). Typically, a delay in reproductive development 346 and reduction in apical dominance are associated with an increase in the number of spikelets 347 and tillers in barley(Digel et al, 2015;Bi et al, 2019).…”

Moving on up – controlling internode growth

“…Subsequent floral development also is dependent on vernalization but requires the long photoperiods of spring (Fjellheim et al, ). Spikelet initiation is independent of photoperiod and advanced by FT3, long photoperiods elevate FT1 and GA to advance floral development, and the TFL1‐like CEN antagonizes both FT1 and FT3 (Boden et al , ; Digel et al , ; Mulki et al , ; Bi et al , ). Plasmodesmata constrict in wheat over winter (Jian & Wang, ), suggesting a seasonal regulation of symplastic continuity in cereals which could influence perception of florigen and CEN/TFL signals.…”