Testing a cytokinin dilution model of floral duration in barley

The seeds and fruit produced by flowering in plants provides the vast majority of calories consumed by human societies. Plants attempt to optimize their reproductive success by correctly timing the initiation and duration of flowering, to produce the 'correct' number of seed for prevailing environmental conditions. In cereal crops, including the key UK crop barley, the duration of flowering determines the number of flowers formed, and the 'yield potential' of the crop. Using the model plant Arabidopsis thaliana, we have recently shown that the concentration of the plant hormone cytokinin determines how long Arabidopsis flowers for. As cytokinin becomes diluted across the increasingly large shoot system, plants stop producing and opening flowers, leading to the end of flowering. Based on preliminary evidence, we believe that this same mechanism also regulates duration of flowering - and hence yield potential - in cereal crops. We hypothesise that increasing cytokinin sensitivity in cereals will therefore increase the duration of flowering and their yield potential. In this proposal, we aim to test this hypothesis using a combination of high-resolution phenotyping, advanced bioimaging, transcriptomics and classical and molecular genetics. Understanding the mechanisms controlling flowering duration will allow us to challenge current limitations on crop yields, and drive a timely change in yield potential in barley and other key cereal crops. This will help to meet the pressing need to produce more food to feed the growing global population.

Flowering in plants produces the vast majority of calories consumed by human societies. Our recent work has shown that cytokinin signalling regulates the duration and extent of flowering in Arabidopsis, and that enhancing cytokinin sensitivity delays inflorescence arrest and increases yield potential. Furthermore, we have shown that, despite their obvious differences in flowering, this is likely to be a conserved mechanism between monocots and eudicots. To explain duration of flowering in Arabidopsis, we have developed a model in which the progressive dilution of the root-derived trans-Zeatin cytokinin pool among active inflorescences determines the timing of inflorescence and floral meristem arrest. We now want to test how this model applies to the arrest of spike meristems in the key crop species barley, and to understand whether this model explains well-characterised yield trade-offs observed in six-rowed barley cultivars. Based on our preliminary data, our central hypothesis is that increasing cytokinin sensitivity in spike meristems will increase the duration of flowering and spikelet number. In this proposal we our aim is to test this hypothesis using high-resolution phenotyping, advanced bioimaging, transcriptomics and classical and molecular genetics. Understanding the mechanisms controlling meristem arrest will allow us to challenge the current 'developmental cap' on cereal crop yields, and drive a timely step change in yield potential in barley and other key cereal crops.