Abstract
BackgroundIn winter barley plants, vernalization and photoperiod cues have to be integrated to promote flowering. Plant development and expression of different flowering promoter (HvVRN1, HvCO2, PPD-H1, HvFT1, HvFT3) and repressor (HvVRN2, HvCO9 and HvOS2) genes were evaluated in two winter barley varieties under: (1) natural increasing photoperiod, without vernalization, and (2) under short day conditions in three insufficient vernalization treatments. These challenging conditions were chosen to capture non-optimal and natural responses, representative of those experienced in the Mediterranean area.ResultsIn absence of vernalization and under increasing photoperiods, HvVRN2 expression increased with day-length, mainly between 12 and 13 h photoperiods in our latitudes. The flowering promoter gene in short days, HvFT3, was only expressed after receiving induction of cold or plant age, which was associated with low transcript levels of HvVRN2 and HvOS2. Under the sub-optimal conditions here described, great differences in development were found between the two winter barley varieties used in the study. Delayed development in ‘Barberousse’ was associated with increased expression levels of HvOS2. Novel variation for HvCO9 and HvOS2 is reported and might explain such differences.ConclusionsThe balance between the expression of flowering promoters and repressor genes regulates the promotion towards flowering or the maintenance of the vegetative state. HvOS2, an ortholog of FLC, appears as a strong candidate to mediate in the vernalization response of barley. Natural variation found would help to exploit the plasticity in development to obtain better-adapted varieties for current and future climate conditions.
Highlights
In winter barley plants, vernalization and photoperiod cues have to be integrated to promote flowering
Gene expression under increasing natural photoperiod In order to determine the day-length threshold that induces the expression of HvVRN2, experiment 1 involved sequential sowings in a greenhouse, one week apart
HvVRN2 gene expression remained low until a surge around sowing event 5 (Fig. 2), coincident with an increase of natural daylight between 12 - 13 h, and a concurrent change of pattern of expression of HvCO2, responding to photoperiod cues, in unvernalized conditions. We propose that these events indicate an important shift in gene expression patterns in winter barleys, which could have an effect in plant development
Summary
Vernalization and photoperiod cues have to be integrated to promote flowering. Plant development and expression of different flowering promoter (HvVRN1, HvCO2, PPD-H1, HvFT1, HvFT3) and repressor (HvVRN2, HvCO9 and HvOS2) genes were evaluated in two winter barley varieties under: (1) natural increasing photoperiod, without vernalization, and (2) under short day conditions in three insufficient vernalization treatments These challenging conditions were chosen to capture non-optimal and natural responses, representative of those experienced in the Mediterranean area. Winter cereals need a period of exposure to low temperature (vernalization), which must be completed in a timely manner so the plant is Monteagudo et al BMC Plant Biology (2019) 19:113 responses tuned to the needs of each specific region [4] For this reason, plant breeding for upcoming conditions demands comprehensive studies on the effect of photoperiod on major flowering genes, and their interaction with the vernalization pathway. Special emphasis should be given to environmental conditions closer to natural ones, as it is not known “whether the current model of photoperiodic flowering regulation can recapitulate the seasonal flowering mechanisms in complicated natural LD environments” [5]
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