Global Transcriptome Profiling of Developing Leaf and Shoot Apices Reveals Distinct Genetic and Environmental Control of Floral Transition and Inflorescence Development in Barley

Abstract

Timing of the floral transition and inflorescence development strongly affect yield in barley (Hordeum vulgare). Therefore, we examined the effects of daylength and the photoperiod response gene PHOTOPERIOD1 (Ppd-H1) on barley development and analyzed gene expression changes in the developing leaves and main shoot apices (MSAs) of barley by RNA sequencing. The daylength sensitivity of MSA development had two phases, floret primordia initiated under long and short days, whereas successful inflorescence development occurred only under long days. The transcripts associated with floral transition were largely regulated independently of photoperiod and allelic variation at Ppd-H1. The photoperiod-and Ppd-H1-dependent differences in inflorescence development and flower fertility were associated with the induction of barley FLOWERING LOCUS T orthologs: FT1 in leaves and FT2 in MSAs. FT1 expression was coregulated with transcripts involved in nutrient transport, carbohydrate metabolism, and cell cycle regulation, suggesting that FT1 might alter source-sink relationships. Successful inflorescence development correlated with upregulation of FT2 and transcripts related to floral organ development, phytohormones, and cell cycle regulation. Identification of photoperiod and stage-specific transcripts gives insights into the regulation of reproductive development in barley and provides a resource for investigation of the complexities of development and yield in temperate grasses.

The Genetic Control of Reproductive Development under High Ambient Temperature

“…This indicated that Ppd-H1 and HvELF3 controlled the relative expression levels of BM genes under different ambient temperature conditions. HvBM3 and HvBM8 are known targets of Ppd-H1 under LD conditions and their expression patterns correlate with the development of the inflorescence (Digel et al, 2015(Digel et al, , 2016. In this study, we show that the effect of Ppd-H1 on HvBM3 and HvBM8 expression and flowering time was temperature dependent.…”

“…The authors suggested an interaction between the photoperiod and thermosensitive pathway. Our study demonstrates that this interaction is mediated by Ppd-H1, which is functional under LDs, but not under SDs (Digel et al, 2015). Furthermore, we show that the effect of Ppd-H1 on early reproductive development under high temperatures is dependent on HvVRN1.…”

“…Most commonly, flowering is scored as heading in barley. However, the different phases of shoot apex development differ in their sensitivity to environmental cues and are controlled by different genetic factors, so that floral transition and flowering may not be correlated and separated in time by many weeks (Digel et al, 2015). Variation in the timing of different developmental phases in turn affects the number of floret primordia, fertile flowers, and seeds per spike (Digel et al, 2015).…”

“…However, the different phases of shoot apex development differ in their sensitivity to environmental cues and are controlled by different genetic factors, so that floral transition and flowering may not be correlated and separated in time by many weeks (Digel et al, 2015). Variation in the timing of different developmental phases in turn affects the number of floret primordia, fertile flowers, and seeds per spike (Digel et al, 2015). To better understand the effects of temperature on development, it is therefore important to investigate the effects of environmental and genetic variation on individual phases of shoot apex development.…”

Photoperiod-H1 (Ppd-H1) Controls Leaf Size

“…However, in our experiments, Ppd-H1-dependent differences in leaf size were cumulative and increased with leaf number on the main stem. While Ppd-H1 does not have a strong effect on the vegetative-to-reproductive phase change, it strongly controls inflorescence development and stem elongation (Digel et al, 2015). Differences in the rate of leaf emergence, in the duration of leaf growth, and in the final leaf cell number suggested that Ppd-H1 affected leaf size by influencing the rate of agedependent progression of leaf development.…”