UV-B antagonises shade avoidance and increases levels of the flavonoid quercetin in coriander (Coriandrum sativum)

Abstract

Despite controlling a diverse array of regulatory processes in plants, UV-B wavelengths (280-315 nm)are attenuated by common greenhouse materials such as glass and polycarbonate and are therefore depleted in many commercial growing environments. In this study, we analysed the architecture, pigment accumulation and antioxidant capacity of coriander (Coriandrum sativum, also known as cilantro) plants grown with and without supplementary UV-B (1.5 µmol m −2 s −1 ). We demonstrate that UV-B limits stem elongation responses to neighbour proximity perception (shade avoidance), promoting a more compact plant architecture. In addition, UV-B increased leaf quercetin content and total antioxidant capacity. Arabidopsis thaliana mutants deficient in flavonoid biosynthesis were not impaired in shade avoidance inhibition, suggesting that UV-B-induced flavonoid synthesis is not a component of this response. Our results indicate that UV-B supplementation may provide a method to manipulate the architecture, flavour and nutritional content of potted herbs whilst reducing the deleterious impacts of dense planting on product quality.UV-B comprises less than 1% of sunlight, yet regulates a wide range of physiological and developmental processes in plants. These include the production of protective sunscreen compounds, plant growth, photosynthesis, stomatal regulation and defence against pests and pathogens 1 . In Arabidopsis, photomorphogenic UV-B signals are perceived by the photoreceptor UV RESISTANCE LOCUS 8 (UVR8) 2 . Upon UV-B absorption, UVR8 dimers monomerise and interact with the E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) to initiate the transcriptional regulation of hundreds of genes 3 . The most striking phenotype displayed by UV-B-treated plants is a reduction in plant size, resulting from reduced leaf expansion and an inhibition of stem elongation 4,5 . This is most apparent in environmental conditions whereby stem elongation is promoted, such as exposure to low red to far red ratio light (low R:FR) 5 , and high temperature 6 . Low R:FR is a component of vegetational shade and a signal of neighbour proximity prior to shading 7 . Plant perception of reduced R:FR by phytochrome photoreceptors leads to a rapid elongation of stems, as plants attempt to overtop neighbours. This response is largely driven by an increase in auxin synthesis, via low R:FR-mediated stabilisation and activation of PHYTOCHROME INTERACTING FACTOR (PIF) transcription factors 7 . UV-B perceived by UVR8 decreases auxin activity by reducing PIF4/5 abundance and activity. This is achieved by promoting PIF degradation 5 , increasing levels of ELONGATED HYPOCOTYL 5 (HY5) transcription factor (which competes with PIF4 for target promoters) 8 and increasing levels of growth-suppressing DELLA proteins which bind to PIFs, inhibiting their function and promoting their degradation 5,9,10 .Control of stem length is a key objective in horticulture, where the aesthetic quality of plants is paramount to commercial success. Excessive stem growth can ...

Exotic plant species are locally adapted but not to high ultraviolet‐B radiation: a reciprocal multispecies experiment

“…To elucidate the causal dependency here, one would have to additionally compare fitness traits, e.g., investment in reproductive biomass or number of fertile seeds, and thus test whether fitness is also reduced or being maintained. In contrast to previous studies (Robson et al 2015, Fraser et al 2017, German individuals did not show any plant architecture change in response to UV radiation that might hint at a lack of necessity regarding strong photoprotection in their home range. However, both strategies might be a consequence of local selection due to ambient UV-B radiation intensities in the respective home range, as different UV response patterns of German and New Zealand individuals across the UV treatments clearly displayed differentiation of origins within species that is less likely to be affected by other local environmental factors.…”

“…, Fraser et al. ), German individuals did not show any plant architecture change in response to UV radiation that might hint at a lack of necessity regarding strong photoprotection in their home range. However, both strategies might be a consequence of local selection due to ambient UV‐B radiation intensities in the respective home range, as different UV response patterns of German and New Zealand individuals across the UV treatments clearly displayed differentiation of origins within species that is less likely to be affected by other local environmental factors.…”

Pre-Harvest UV-B Radiation and Photosynthetic Photon Flux Density Interactively Affect Plant Photosynthesis, Growth, and Secondary Metabolites Accumulation in Basil (Ocimum basilicum) Plants

“…Kaiserli (2018) reported that most cell-wall elongation genes induced by BRI1-EMS-SUPPRESSOR 1 (BES1) are negatively regulated by UV-B radiation [45]. Meanwhile, the biosynthesis and signaling of plant growth hormone auxin, a key regulator of stem elongation, was also suppressed in arabidopsis (Arabidopsis thaliana) and coriander (Coriandrum sativum) plants after UV-B radiation, thereby reducing plant stem elongation and promoting a compact phenotype [46]. In the present study, similar results such as reduced leaf area, increased leaf thickness, accumulation of leaf surface waxes, and reduced leaf internode length were observed, which are plant acclimation responses to supplemental UV-B radiation.…”

“…Ghasemzadeh et al (2016) reported that total phenolic and flavonoid content in green basil plants increased by 16% and 85%, respectively, after a 13 kJ•m −2 •h −1 post-harvest UV-B radiation for 4-10 h, but anthocyanin content was not measured [52]. It was also reported that upon supplemental UV-B radiation, the gene expression of phenylalanine ammonia lyase (PAL) and chalcone synthase (CHS), two key molecular markers for phenolic compounds biosynthesis increased significantly [46,53]. Noticeably, in the present study, the enhancement of flavonoids and phenolics by UV-B radiation was much greater than anthocyanin.…”

Deciphering the high‐quality genome sequence of coriander that causes controversial feelings

“…The Apiaceae family contains additional economically important plants, such as ajwain, angelica, anise, asafoetida, caraway and chervil (Feng et al, ; Que et al, ; Shelef, ). In recent years, a large number of studies have been reported on the phenotype, physiology, stress resistance, gene expression and metabolite identification of coriander (Abbassi et al, ; AlQuraidi et al, ; Choudhary et al, ; Divya et al, ; Fraser et al, ; Gholizadeh et al, ; Verma et al, ). However, among all the Apiaceae species, only the carrot genome has been sequenced until now (Iorizzo et al, ).…”