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Plants require the UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) for acclimation and survival in sunlight. Upon UV-B perception, UVR8 switches instantaneously from a homodimeric to monomeric configuration, which leads to interaction with the key signaling protein CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and induction of UV-B–protective responses. Here, we show that UVR8 monomerization is reversible in vivo, restoring the homodimeric ground state. We also demonstrate that the UVR8-interacting proteins REPRESSOR OF UV-B PHOTOMORPHOGENESIS (RUP)1 and RUP2 mediate UVR8 redimerization independently of COP1. UVR8 redimerization consequently disrupts the UVR8–COP1 interaction, which halts signaling. Our results identify a key role of RUP1- and RUP2-mediated UVR8 redimerization in photoreceptor inactivation, a crucial process that regenerates reactivatable UVR8 homodimers.

Plants respond to low levels of UV-B radiation with a coordinated photomorphogenic response that allows acclimation to this environmental stress factor. The key players in this UV-B response are COP1 (an E3 ubiquitin ligase), UVR8 (a β-propeller protein), and HY5 (a bZIP transcription factor). We have shown previously that an elevated UV-B-specific response is associated with dwarf growth, indicating the importance of balancing UV-B-specific signaling. Negative regulators of this pathway are not known, however. Here, we describe two highly related WD40-repeat proteins, REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1) and RUP2, that interact directly with UVR8 as potent repressors of UV-B signaling. Both genes were transcriptionally activated by UV-B in a COP1-, UVR8-, and HY5-dependent manner. rup1 rup2 double mutants showed an enhanced response to UV-B and elevated UV-B tolerance after acclimation. Overexpression of RUP2 resulted in reduced UV-B-induced photomorphogenesis and impaired acclimation, leading to hypersensitivity to UV-B stress. These results are consistent with an important regulatory role for RUP1 and RUP2, which act downstream of UVR8-COP1 in a negative feedback loop impinging on UVR8 function, balancing UV-B defense measures and plant growth.

Arabidopsis thaliana UV RESISTANCE LOCUS 8 (UVR8) is a UV-B photoreceptor that initiates photomorphogenic responses underlying acclimation and UV-B tolerance in plants. UVR8 is a homodimer in its ground state, and UV-B exposure results in its instantaneous monomerization followed by interaction with CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1), a major factor in UV-B signaling. UV-B photoreception by UVR8 is based on intrinsic tryptophan aromatic amino acid residues, with tryptophan-285 as the main chromophore. We generated transgenic plants expressing UVR8 with a single amino acid change of tryptophan-285 to alanine. UVR8 ᵂ²⁸⁵ᴬ appears monomeric and shows UV-B–independent interaction with COP1. Phenotypically, the plants expressing UVR8 ᵂ²⁸⁵ᴬ exhibit constitutive photomorphogenesis associated with constitutive activation of target genes, elevated levels of anthocyanins, and enhanced, acclimation-independent UV-B tolerance. Moreover, we have identified COP1, REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 and 2 (RUP1 and RUP2), and the SUPPRESSOR OF PHYA-105 (SPA) family as proteins copurifying with UVR8 ᵂ²⁸⁵ᴬ. Whereas COP1, RUP1, and RUP2 are known to directly interact with UVR8, we show that SPA1 interacts with UVR8 indirectly through COP1. We conclude that UVR8 ᵂ²⁸⁵ᴬ is a constitutively active UVR8 photoreceptor variant in Arabidopsis , as is consistent with the crucial importance of monomer formation and COP1 binding for UVR8 activity.

Members of the cryptochrome/photolyase family (CPF) are widely distributed throughout all kingdoms, and encode photosensitive proteins that typically show either photoreceptor or DNA repair activity. Animal and plant cryptochromes have lost DNA repair activity and now perform specialized photoperceptory functions, for example, plant cryptochromes regulate growth and circadian rhythms, whereas mammalian and insect cryptochromes act as transcriptional repressors that control the circadian clock. However, the functional differentiation between photolyases and cryptochromes is now being questioned. Here, we show that the PtCPF1 protein from the marine diatom Phaeodactylum tricornutum shows 6‐4 photoproduct repair activity and can act as a transcriptional repressor of the circadian clock in a heterologous mammalian cell system. Conversely, it seems to have a wide role in blue‐light‐regulated gene expression in diatoms. The protein might therefore represent a missing link in the evolution of CPFs, and act as a novel ultraviolet/blue light sensor in marine environments.

The smallest known eukaryotes, at ≈1-μm diameter, are Ostreococcus tauri and related species of marine phytoplankton. The genome of Ostreococcus lucimarinus has been completed and compared with that of O. tauri. This comparison reveals surprising differences across orthologous chromosomes in the two species from highly syntenic chromosomes in most cases to chromosomes with almost no similarity. Species divergence in these phytoplankton is occurring through multiple mechanisms acting differently on different chromosomes and likely including acquisition of new genes through horizontal gene transfer. We speculate that this latter process may be involved in altering the cell-surface characteristics of each species. In addition, the genome of O. lucimarinus provides insights into the unique metal metabolism of these organisms, which are predicted to have a large number of selenocysteine-containing proteins. Selenoenzymes are more catalytically active than similar enzymes lacking selenium, and thus the cell may require less of that protein. As reported here, selenoenzymes, novel fusion proteins, and loss of some major protein families including ones associated with chromatin are likely important adaptations for achieving a small cell size.

Diatoms are largely responsible for production of biogenic silica in the global ocean. However, in surface seawater, Si(OH)(4) can be a major limiting factor for diatom productivity. Analyzing at the global scale the genes networks involved in Si transport and metabolism is critical in order to elucidate Si biomineralization, and to understand diatoms contribution to biogeochemical cycles. Using whole genome expression analyses we evaluated the transcriptional response to Si availability for the model species Phaeodactylum tricornutum. Among the differentially regulated genes we found genes involved in glutamine-nitrogen pathways, encoding putative extracellular matrix components, or involved in iron regulation. Some of these compounds may be good candidates for intracellular intermediates involved in silicic acid storage and/or intracellular transport, which are very important processes that remain mysterious in diatoms. Expression analyses and localization studies gave the first picture of the spatial distribution of a silicic acid transporter in a diatom model species, and support the existence of transcriptional and post-transcriptional regulations. Our global analyses revealed that about one fourth of the differentially expressed genes are organized in clusters, underlying a possible evolution of P. tricornutum genome, and perhaps other pennate diatoms, toward a better optimization of its response to variable environmental stimuli. High fitness and adaptation of diatoms to various Si levels in marine environments might arise in part by global regulations from gene (expression level) to genomic (organization in clusters, dosage compensation by gene duplication), and by post-transcriptional regulation and spatial distribution of SIT proteins.

Grass pea (Lathyrus sativus L.) is a Neolithic plant that has survived millennia of cultivation and has spread over three continents. It is a robust legume crop that is considered one of the most resilient to climate changes and to be survival food during drought-triggered famines. The hardy penetrating root system allows the cultivation of grass pea in various soil types, including marginal ones. As an efficient nitrogen fixer, it meets its own nitrogen requirements and positively benefits subsequent crops. However, already in ancient India and Greece, overconsumption of the seeds and a crippling neurological disorder, later coined neurolathyrism, had been linked. Overemphasis of their suspected toxic properties has led to disregard the plant’s exceptionally positive agronomic properties and dietary advantages. In normal socio-economic and environmental situations, in which grass pea is part of a balanced diet, neurolathyrism is virtually non-existent. The etiology of neurolathyrism has been oversimplified and the deficiency in methionine in the diet has been overlooked. In view of the global climate change, this very adaptable and nutritious orphan crop deserves more attention. Grass pea can become a wonder crop if the double stigma on its reputation as a toxic plant and as food of the poor can be disregarded. Additionally, recent research has exposed the potential of grass pea as a health-promoting nutraceutical. Development of varieties with an improved balance in essential amino acids and diet may be relevant to enhance the nutritional value without jeopardizing the multiple stress tolerance of this promising crop.

More than 20 years ago, the first genetically modified (GM) plants entered the seed market. The patents covering the first GM plants have begun to expire and these can now be considered as Off-Patent Events. Here we describe the challenges that will be faced by a Secondary Party by further use and development of these Off-Patent Events. Indeed, the conditions for Off-Patent Events are not available yet to form the basis for a new viable industry similar to the generic manufacturers of agrochemicals or pharmaceutical products, primarily because of (i) unharmonized global regulatory requirements for GM organisms, (ii) inaccessibility of regulatory submissions and data, and (iii) potential difficulties to obtain seeds and genetic material of the unique genotypes used to generate regulatory data. We propose certain adaptations by comparing what has been done in the agrochemical and pharmaceutical markets to facilitate the development of generics. Finally, we present opportunities that still exist for further development of Off-Patent Events in collaboration with Proprietary Regulatory Property Holders in emerging markets, provided (i) various countries approve these events without additional regulatory burdens (i.e., acceptance of the concept of data transportability), and (ii) local breeders agree to meet product stewardship requirements.

On August 30-31, 2018, a two-day symposium took place in Ghent (Belgium) with the aim of deliberating on scientific innovation for the development of a sustainable agriculture in Africa. This symposium was attended by African and European scientists, representing both the public and private sectors. Topics included relevant crops for Africa, soil quality, biotic and abiotic stresses, and human and animal health; and were all handled in light of a critical assessment of how research and scientific innovation could tackle the challenges encountered in crop production. Development of a sustainable agriculture that could provide high-quality food for the population is often attempted with two different mindsets. These approaches, as presented by Charles Mann in his book The wizard and the prophet (2018) are on the one hand the wizard approach, represented by Norman Borlaug and on the other the prophet approach, represented by William Vogt.