Adaptation of barley to mild winters: A role for PPDH2

Abstract

BackgroundUnderstanding the adaptation of cereals to environmental conditions is one of the key areas in which plant science can contribute to tackling challenges presented by climate change. Temperature and day length are the main environmental regulators of flowering and drivers of adaptation in temperate cereals. The major genes that control flowering time in barley in response to environmental cues are VRNH1, VRNH2, VRNH3, PPDH1, and PPDH2 (candidate gene HvFT3). These genes from the vernalization and photoperiod pathways show complex interactions to promote flowering that are still not understood fully. In particular, PPDH2 function is assumed to be limited to the ability of a short photoperiod to promote flowering. Evidence from the fields of biodiversity, ecogeography, agronomy, and molecular genetics was combined to obtain a more complete overview of the potential role of PPDH2 in environmental adaptation in barley.ResultsThe dominant PPDH2 allele is represented widely in spring barley cultivars but is found only occasionally in modern winter cultivars that have strong vernalization requirements. However, old landraces from the Iberian Peninsula, which also have a vernalization requirement, possess this allele at a much higher frequency than modern winter barley cultivars. Under field conditions in which the vernalization requirement of winter cultivars is not satisfied, the dominant PPDH2 allele promotes flowering, even under increasing photoperiods above 12 h. This hypothesis was supported by expression analysis of vernalization-responsive genotypes. When the dominant allele of PPDH2 was expressed, this was associated with enhanced levels of VRNH1 and VRNH3 expression. Expression of these two genes is needed for the induction of flowering. Therefore, both in the field and under controlled conditions, PPDH2 has an effect of promotion of flowering.ConclusionsThe dominant, ancestral, allele of PPDH2 is prevalent in southern European barley germplasm. The presence of the dominant allele is associated with early expression of VRNH1 and early flowering. We propose that PPDH2 promotes flowering of winter cultivars under all non-inductive conditions, i.e. under short days or long days in plants that have not satisfied their vernalization requirement. This mechanism is indicated to be a component of an adaptation syndrome of barley to Mediterranean conditions.

Impact of Pre-Anthesis Water Deficit on Yield and Yield Components in Barley (Hordeum vulgare L.) Plants Grown under Controlled Conditions

“…This might highlight the importance of the PPDH2 in promoting flowering under mild winter conditions. This result is supported by the frequency of a functional PPDH2 allele in winter barley germplasm from the Mediterranean basin [24]. It was proposed that PPDH2 promotes flowering under short-day conditions irrespective to photoperiod conditions and vernalization [24,25].…”

“…This result is supported by the frequency of a functional PPDH2 allele in winter barley germplasm from the Mediterranean basin [24]. It was proposed that PPDH2 promotes flowering under short-day conditions irrespective to photoperiod conditions and vernalization [24,25]. Furthermore, PPDH2 was reported to have a pronounced effect on the heading date in a Morex X Steptoe population grown under short-day conditions [26].…”

The USDA Barley Core Collection: Genetic Diversity, Population Structure, and Potential for Genome-Wide Association Studies

“…Most accessions from Mediterranean countries belong to subpopulation 1 and are six-rows. In general, germplasm from this region is distinct from Central and Northern European accessions in terms of adaptation to the mild winters and hot summers that are characteristic of the Mediterranean climate [59]. Many accessions from Central and South America, as well as Mexico and California, belong to this subpopulation.…”

Photoperiod-H1 (Ppd-H1) Controls Leaf Size

“…However, these cultivars clearly clustered with winter barley genotypes in a principal component analysis of a comprehensive panel of spring and winter varieties (data not shown). A reduced vernalization response in winter barley might offer advantages in autumn-sowing areas with mild winters, which are not as cold as those in more northern or continental climates (Casao et al, 2011). The mutated ppd-H1 allele was present in approximately 25% of the winter barley lines and was preferentially detected in two-rowed genotypes used for malt production.…”