Integration of UV-B and temperature signalling in plants

Light and temperature are two of the most important signals regulating plant development. Thermomorphogenesis (developmental adaptation to non-stressful changes in ambient temperature) is a rapidly expanding field in plant biology with direct applications to crop productivity, ecology and biodiversity management in a changing climate. Although interactions between red/blue photoreceptors and high temperature signalling pathways have been identified, the integration of UV-B and high temperature signalling remains poorly characterised. In sunlight-grown plants, leaf temperature increases concomitantly with UV-B absorption. In contrast to the situation in the field, the majority of plant science is carried out in glasshouses and growth cabinets, conditions in which plants are exposed to little or no UV-B. Understanding how UV-B and high temperature signals are integrated is therefore central to our understanding of plant development in natural environments.

Our recently published work has identified a novel molecular mechanism through which UV-B, perceived by the UVR8 photoreceptor, inhibits high temperature-induced stem elongation. This provides plants with an important braking mechanism in bright sunlight, preventing excessive stem growth which could lead to lodging and critical reductions in biomass. The proposed programme will build on these findings to gain deeper molecular understanding of UV-B and temperature signal crosstalk. In particular, we wish to understand how UV-B regulates the transcript abundance and protein activity of the transcription factor, PIF4. Our results will have direct relevance to existing industrial collaborations aiming to reduce stem elongation in commercial horticulture, through UV-B supplementation.

Elucidating how plants integrate UV-B and temperature signals is fundamental to understanding plant growth and development in sunlight. Towards this aim, we have recently shown that low dose UV-B, perceived by UVR8, inhibits high temperature-mediated stem elongation through suppressing the transcript abundance and activity of the bHLH transcription factor, PIF4. This reduces auxin biosynthesis, limiting cell elongation. This project aims to deepen molecular understanding of this process by firstly establishing whether UV-B regulates PIF4 promoter activity, transcript stability and/or histone acetylation. We will then dissect the molecular mechanisms through which UV-B regulates PIF4 protein activity at different temperatures. These include protein degradation, altered stability of the PIF4 inhibitor, HFR1 and a novel mechanism involving the bZIP transcription factor HYH.

Plant UV-B and temperature responses have significant social, economic and ecological importance. In addition to controlling plant growth, both signals regulate plant metabolism, defence and abiotic stress tolerance. These wide-ranging effects make UV-B and temperature signalling prime targets for crop improvement. Furthermore, global warming makes understanding the effects of UV-B and elevated temperature on organisms and ecosystems a subject of key importance to policy makers.

Beneficiaries:

The horticulture/forestry/viticulture industries: The stature and flowering time of glasshouse crops are commonly controlled through light quality manipulations. To date, these have focussed on red to far-red ratio and blue light which have much less potent effects on architecture than UV-B. The establishment of tree saplings and young vines requires tubular plastic shelters which significantly alter the spectra of light reaching plants and create a warm microclimate. Understanding how plants perceive and respond to low doses of UV-B at different temperatures will greatly facilitate the optimal design of plant growth regimes and growth materials (eg. tree shelters). Towards this aim, Franklin has existing BBSRC-supported industrial collaborations with Vitacress and GrowBristol to investigate the effects of UV-B supplementation on glasshouse-grown pot herbs and hydroponically-grown microgreens, respectively (see pathways to impact and letters of support).

Plant breeders: Increased understanding of UV-B signalling at different temperatures will facilitate the design of crops with optimal architecture, increased pest resistance and enhanced tolerance to climate change.

Policy makers: The ability of plants to survive and compete at elevated levels of UV-B and increased temperature will have significant impact on global food security, ecosystems and biodiversity. This project will therefore benefit policy makers, ecologists and conservationists.

Lab staff, postgraduate and undergraduate students: The provision of BBSRC funding will enable the training of both a PDRA and research technician in plant photobiology and a range of molecular biology techniques. This project will also provide training for MSci, undergraduate and summer students.