Identification and characterization of flowering time genes in barley
Despite the prominent role of Ppd-H1 in controlling photoperiodic flowering in barley, relatively little is known about the molecular mechanism by which this gene and other components of the barley circadian clock control flowering. We identified and cloned barley orthologs of known Arabidopsis clock genes which showed a high level of structural homology and conservation of diurnal and circadian expression patterns as compared to Arabidopsis (Campoli et al. 2012b). However, independent duplications/deletions of clock genes in barley as compared to Arabidopsis suggested that these evolved in a lineage specific manner.
We identified EAM8 and EAM10 as a barley orthologs of the Arabidopsis thaliana circadian clock regulator EARLY FLOWERING3 (ELF3) and LUX/ARRHYTHMO, respectively (Faure et al. 2012, Campoli et al. 2013). We show that EAM8 and EAM10 act as repressors of Ppd-H1 and thus control the transcription of the downstream floral activator HvFT1. Both eam8 and eam10 mutants show circadian defects. The selection of independent eam8 mutations suggested that this strategy facilitated short growth-season adaptation, despite the pronounced clock defect. We propose that HvELF3 and HvLUX1 together mediate the light input into the circadian clock by controlling expression of Ppd-H1. We are currently characterizing additional natural barley mutants with day-neutral flowering.
We functionally characterised HvCO1 as the closest barley ortholog of the Arabidopsis photoperiod response gene CONSTANS and its interaction with genetic variation at Ppd-H1 and Vrn-H1 (Campoli et al. 2012a). Over-expression of HvCO1 in the spring barley Golden Promise accelerated time to flowering in long and short day conditions and caused up-regulation of HvFT1. However, the transgenic plants retained a response to photoperiod, suggesting the presence of photoperiod response factors acting downstream of HvCO1 transcription. We are currently analyzing the functional role of HvCO2 and variation in HvCO1 protein for flowering time control.
Genetic dissection of meristem development
We are interested in understanding the effects of natural and induced genetic variation on meristem development in barley. Meristem development in grasses can be morphologically distinguished into 1) the vegetative phase, 2) spike initiation, and 3) spike growth during stem elongation. Over-expression of HvCO1 and natural genetic variation at Ppd-H1 and HvELF3 primarily affected spike development and stem elongation, suggesting that high levels of HvFT1 in these lines had a stronger effect on inflorescence development than on the transition to a reproductive meristem. We conduct global RNA expression analyses in leaf and shoot apical meristems (SAM) of barley lines under different environmental conditions to identify molecular changes during development. In addition, we analyse the genetic variation in axillary meristem development between cultivated and wild barley. Cultivated barley is characterized by low, synchronous tillering which is beneficial for harvesting. In contrary, the wild ancestor Hordeum vulgare spp. spontaneum exhibits more extensive and asynchronous tillering which improves adaptation to stress-prone environments.