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In controlled environment agriculture, customized light treatments using light-emitting diodes are crucial to improving crop yield and quality. Red (R; 600-700 nm) and blue light (B; 400-500 nm) are two major parts of photosynthetically active radiation (PAR), often preferred in crop production. Far-red radiation (FR; 700-800 nm), although not part of PAR, can also affect photosynthesis and can have profound effects on a range of morphological and physiological processes. However, interactions between different red and blue light ratios (R:B) and FR on promoting yield and nutritionally relevant compounds in crops remain unknown. Here, lettuce was grown at 200 µmol m -2 s -1 PAR under three different R:B ratios: R:B 87.5:12.5 (12.5% blue), R:B 75:25 (25% blue), and R:B 60:40 (40% blue) without FR. Each treatment was also performed with supplementary FR (50 µmol m -2 s -1 ; R:B 87.5:12.5 +FR, R:B 75:25 +FR, and R:B 60:40 +FR). White light with and without FR (W and W+FR) were used as control treatments comprising of 72.5% red, 19% green, and 8.5% blue light. Decreasing the R:B ratio from R:B 87.5:12.5 to R:B 60:40 , there was a decrease in fresh weight (20%) and carbohydrate concentration (48% reduction in both sugars and starch), whereas pigment concentrations (anthocyanins, chlorophyll, and carotenoids), phenolic compounds, and various minerals all increased. These results contrasted the effects of FR supplementation in the growth spectra; when supplementing FR to different R:B backgrounds, we found a significant increase in plant fresh weight, dry weight, total soluble sugars, and starch. Additionally, FR decreased concentrations of anthocyanins, phenolic compounds, and various minerals. Although blue light and FR effects appear to directly contrast, blue and FR light did not have interactive effects together when considering plant growth, morphology, and nutritional content. Therefore, the individual benefits of increased blue light fraction and supplementary FR radiation can be combined and used cooperatively to produce crops of desired quality: adding FR increases growth and carbohydrate concentration while increasing the blue fraction increases nutritional value.

[This corrects the article DOI: 10.3389/fpls.2024.1383100.].

Background Oomycetes are a group of filamentous eukaryotic microorganisms that have colonized all terrestrial and oceanic ecosystems, and they include prominent plant pathogens. The Aphanomyces genus is unique in its ability to infect both plant and animal species, and as such exemplifies oomycete versatility in adapting to different hosts and environments. Dissecting the underpinnings of oomycete diversity provides insights into their specificity and pathogenic mechanisms. Results By carrying out genomic analyses of the plant pathogen A. euteiches and the crustacean pathogen A. astaci , we show that host specialization is correlated with specialized secretomes that are adapted to the deconstruction of the plant cell wall in A. euteiches and protein degradation in A. astaci . The A. euteiches genome is characterized by a large repertoire of small secreted protein (SSP)-encoding genes that are highly induced during plant infection, and are not detected in other oomycetes. Functional analysis revealed an SSP from A. euteiches containing a predicted nuclear-localization signal which shuttles to the plant nucleus and increases plant susceptibility to infection. Conclusion Collectively, our results show that Aphanomyces host adaptation is associated with evolution of specialized secretomes and identify SSPs as a new class of putative oomycete effectors.

Abstract Plants detect neighboring competitors through a decrease in the ratio between red and far-red light (R:FR). This decreased R:FR is perceived by phytochrome photoreceptors and triggers shade avoidance responses such as shoot elongation and upward leaf movement (hyponasty). In addition to promoting elongation growth, low R:FR perception enhances plant susceptibility to pathogens: the growth-defense trade-off. Although increased susceptibility in low R:FR has been studied for over a decade, the associated timing of molecular events is still unknown. Here, we studied the chronology of FR-induced susceptibility events in tomato plants pre-exposed to either white light (WL) or WL supplemented with FR light (WL+FR) prior to inoculation with the necrotrophic fungus Botrytis cinerea (B.c.). We monitored the leaf transcriptional changes over a 30-hr time course upon infection and followed up with functional studies to identify mechanisms. We found that FR-induced susceptibility in tomato is linked to a general dampening of B.c.-responsive gene expression, and a delay in both pathogen recognition and jasmonic acid-mediated defense gene expression. In addition, we found that the supplemental FR-induced ethylene emissions affect plant immune responses under WL+FR conditions. This study increases our understanding of the growth-immunity trade-off, while simultaneously providing leads to improve tomato resistance against pathogens in dense cropping systems. One-sentence summary Low Red:Far-red ratio enhances tomato susceptibility towards the necrotrophic fungus Botrytis cinerea via delayed early pathogen detection and dampening of jasmonic acid-mediated defense activation. Footnotes * ↵* Author for contact: Prof. dr. Ronald Pierik, Tel: +31 30 253 6838, Email: r.pierik{at}uu.nl

Plants lacking phytochrome photoreceptors display elevated soluble sugar levels in leaves. Although pathogens principally feed on sugars supplied by the plant, the link between increased plant sugar levels upon phytochrome inactivation and disease development has not been considered. Tomato plants were exposed to control white LED (WL) or a combination of white and far-red LED (WL+FR) light, to inactivate phytochrome signaling and modulate soluble sugar levels. We also experimentally manipulated internal sugar levels by either supplementing glucose or inhibiting photosynthesis in tomato leaflets prior to performing soluble sugar quantifications or bioassays with pathogens with distinct lifestyles. Tomato plants exposed to WL+FR or lacking phytochrome B (phyB1phyB2 double mutants) show enhanced levels of soluble sugars, especially glucose and fructose, in their leaves. The jasmonic acid biosynthesis mutant def1 also has elevated soluble sugar levels which could be rescued by exogenous methyl-jasmonate application. This indicates an interplay between JA signaling and primary metabolism. The increase in soluble sugar levels in tomato leaves upon phytochrome inactivation is regulated in a JA-dependent manner. Our data stress the importance of primary metabolism in the FR-induced susceptibility in tomato that could contribute to promote plant resistance when grown at high density. Competing Interest Statement The authors have declared no competing interest.