Ppd-H1integrates drought stress signals to control spike development and flowering time in barley

Abstract

Drought impairs growth and spike development, and is therefore a major cause of yield losses in the temperate cereals barley and wheat. Here, we show that the photoperiod response gene PHOTOPERIOD-H1 (Ppd-H1) interacts with drought stress signals to modulate spike development. We tested the effects of a continuous mild and a transient severe drought stress on developmental timing and spike development in spring barley cultivars with a natural mutation in ppd-H1 and derived introgression lines carrying the wild-type Ppd-H1 allele from wild barley. Mild drought reduced the spikelet number and delayed floral development in spring cultivars but not in the introgression lines with a wild-type Ppd-H1 allele. Similarly, drought-triggered reductions in plant height, and tiller and spike number were more pronounced in the parental lines compared with the introgression lines. Transient severe stress halted growth and floral development; upon rewatering, introgression lines, but not the spring cultivars, accelerated development so that control and stressed plants flowered almost simultaneously. These genetic differences in development were correlated with a differential down-regulation of the flowering promotors FLOWERING LOCUS T1 and the BARLEY MADS-box genes BM3 and BM8. Our findings therefore demonstrate that Ppd-H1 affects developmental plasticity in response to drought in barley.

Agronomic Performance and Flowering Behavior in Response to Photoperiod and Vernalization in Barley (Hordeum vulgare L.) Genotypes with Contrasting Drought Tolerance Behavior

“…This could explain the faster transition to the reproductive stage that occurred in Rum compared to Steptoe under LD and SD conditions and particularly in response to drought stress under SD conditions. Such differences in Vrn-H1 gene expression between genotypes were reported previously where higher expression levels were detected in S42-IL107 compared with Scarlett under LD conditions irrespective of drought treatment [21].…”

“…This could explain the faster transition to the reproductive stage that occurred in Rum compared to Steptoe under LD and SD conditions and particularly in response to drought stress under SD conditions. Such differences in Vrn-H1 gene expression between genotypes were reported previously where higher expression levels were detected in S42-IL107 compared with Scarlett under LD conditions irrespective of drought treatment [21]. In this study, both tested genotypes carried different Vrn-H1 alleles where Rum has an insertion (Vrn-H1-7) and Steptoe has a deletion (Vrn-H1-4) at Vrn-H1 rst intron [22], which might explain the differential gene expression in response to different treatments.…”

“…A similar trend was reported by [51] where the developmental stage of the apical meristem was similar in introgression lines carrying Ppd-H1 under control and stress conditions. In a recent study, [21] found that the expression of Ppd-H1 was not affected in response to drought under LD conditions in two tested genotypes. Still, the same study concluded that Ppd-H1 integrates photoperiod and drought stress signals to ne-tune reproductive development in barley.…”

“…Allelic differences and their combinations in vernalization-(VRN) and photoperiodrelated (PPD) genes seem to have a large effect on stress tolerance in temperate cereals [18,19]. For instance, the PHOTOPERIOD-H1 (Ppd-H1) gene was found to control stress-induced senescence in barley roots subjected to osmotic stress [20] and most recently it was found to control the plasticity of development in response to drought [21]. In another study, barley genotypes carrying spring VERNALIZATION-H1 (Vrn-H1) alleles showed an accelerated owering under drought stress when compared with genotypes carrying winter alleles [22].…”

FLOWERING LOCUS T4delays flowering and decreases floret fertility in barley

“…The null segregant sister line without the transgene was used as a control together with Golden Promise. Golden Promise is a spring barley with a mutation in the CCT domain of Ppd-H1 , a deletion of the vernalization gene VRN-H2 , and a deletion in the first regulatory intron of the vernalization gene VRN-H1 ( Mulki et al , 2018 ; Gol et al , 2021 ). Golden Promise therefore does not need vernalization to flower and is characterized by a reduced induction of the HvFT1 and late flowering under LD conditions.…”