Reducing PHYTOENE SYNTHASE activity fine-tunes the abundance of a cis-carotene-derived signal that regulates the PIF3/HY5 module and plastid biogenesis.

PHYTOENE SYNTHASE (PSY) is a rate-limiting enzyme catalysing the first committed step of carotenoid biosynthesis, and changes in PSY gene expression and/or protein activity alter carotenoid composition and plastid differentiation in plants. Four genetic variants of PSY (psy-4, psy-90, psy-130, and psy-145) were identified using a forward genetics approach that rescued leaf virescence phenotypes and plastid abnormalities displayed by the Arabidopsis CAROTENOID ISOMERASE (CRTISO) mutant ccr2 (carotenoid and chloroplast regulation 2) when grown under a shorter photoperiod. The four non-lethal mutations affected alternative splicing, enzyme-substrate interactions, and PSY:ORANGE multi-enzyme complex binding, constituting the dynamic post-transcriptional fine-tuning of PSY levels and activity without changing localization to the stroma and protothylakoid membranes. psy genetic variants did not alter total xanthophyll or ß-carotene accumulation in ccr2, yet they reduced specific acyclic linear cis-carotenes linked to the biosynthesis of a currently unidentified apocarotenoid signal regulating plastid biogenesis, chlorophyll biosynthesis, and photomorphogenic regulation. ccr2 psy variants modulated the PHYTOCHROME-INTERACTING FACTOR 3/ELONGATED HYPOCOTYL 5 (PIF3/HY5) ratio, and displayed a normal prolamellar body formation in etioplasts and chlorophyll accumulation during seedling photomorphogenesis. Thus, suppressing PSY activity and impairing PSY:ORANGE protein interactions revealed how cis-carotene abundance can be fine-tuned through holoenzyme-metabolon interactions to control plastid development.

Abscisic acid supports colonization of Eucalyptus grandis roots by the mutualistic ectomycorrhizal fungus Pisolithus microcarpus.

The pathways regulated in ectomycorrhizal (EcM) plant hosts during the establishment of symbiosis are not as well understood when compared to the functional stages of this mutualistic interaction. Our study used the EcM host Eucalyptus grandis to elucidate symbiosis-regulated pathways across the three phases of this interaction. Using a combination of RNA sequencing and metabolomics we studied both stage-specific and core responses of E. grandis during colonization by Pisolithus microcarpus. Using exogenous manipulation of the abscisic acid (ABA), we studied the role of this pathway during symbiosis establishment. Despite the mutualistic nature of this symbiosis, a large number of disease signalling TIR-NBS-LRR genes were induced. The transcriptional regulation in E. grandis was found to be dynamic across colonization with a small core of genes consistently regulated at all stages. Genes associated to the carotenoid/ABA pathway were found within this core and ABA concentrations increased during fungal integration into the root. Supplementation of ABA led to improved accommodation of P. microcarpus into E. grandis roots. The carotenoid pathway is a core response of an EcM host to its symbiont and highlights the need to understand the role of the stress hormone ABA in controlling host-EcM fungal interactions.

Mechanical stress acclimation in plants: Linking hormones and somatic memory to thigmomorphogenesis.

A single event of mechanical stimulation is perceived by mechanoreceptors that transduce rapid transient signalling to regulate gene expression. Prolonged mechanical stress for days to weeks culminates in cellular changes that strengthen the plant architecture leading to thigmomorphogenesis. The convergence of multiple signalling pathways regulates mechanically induced tolerance to numerous biotic and abiotic stresses. Emerging evidence showed prolonged mechanical stimulation can modify the baseline level of gene expression in naive tissues, heighten gene expression, and prime disease resistance upon a subsequent pathogen encounter. The phenotypes of thigmomorphogenesis can persist throughout growth without continued stimulation, revealing somatic-stress memory. Epigenetic processes regulate TOUCH gene expression and could program transcriptional memory in differentiating cells to program thigmomorphogenesis. We discuss the early perception, gene regulatory and phytohormone pathways that facilitate thigmomorphogenesis and mechanical stress acclimation in Arabidopsis and other plant species. We provide insights regarding: (1) the regulatory mechanisms induced by single or prolonged events of mechanical stress, (2) how mechanical stress confers transcriptional memory to induce cross-acclimation to future stress, and (3) why thigmomorphogenesis might resemble an epigenetic phenomenon. Deeper knowledge of how prolonged mechanical stimulation programs somatic memory and primes defence acclimation could transform solutions to improve agricultural sustainability in stressful environments.

Smart glass impacts stomatal sensitivity of greenhouse Capsicum through altered light.

Optical films that alter light transmittance may reduce energy consumption in high-tech greenhouses, but their impact on crop physiology remains unclear. We compared the stomatal responses of Capsicum plants grown hydroponically under control glass (70% diffuse light) or the smart glass (SG) film ULR-80, which blocked >50% of short-wave radiation and ~9% of photosynthetically active radiation (PAR). SG had no significant effects on steady-state (gs) or maximal (gmax) stomatal conductance. In contrast, SG reduced stomatal pore size and sensitivity to exogenous abscisic acid (ABA), thereby increasing rates of leaf water loss, guard cell K+ and Cl- efflux, and Ca2+ influx. SG induced faster stomatal closing and opening rates on transition between low (100 µmol m-2 s-1) and high PAR (1500 µmol m-2 s-1), which compromised water use efficiency relative to control plants. The fraction of blue light (0% or 10%) did not affect gs in either treatment. Increased expression of stomatal closure and photoreceptor genes in epidermal peels of SG plants is consistent with fast stomatal responses to light changes. In conclusion, stomatal responses of Capsicum to SG were more affected by changes in light intensity than spectral quality, and re-engineering of the SG should maximize PAR transmission, and hence CO2 assimilation.

Anti-herbivore silicon defences in a model grass are greatest under Miocene levels of atmospheric CO2.

Silicon (Si) has an important role in mitigating diverse biotic and abiotic stresses in plants, mainly via the silicification of plant tissues. Environmental changes such as atmospheric CO2 concentrations may affect grass Si concentrations which, in turn, can alter herbivore performance. We recently demonstrated that pre-industrial atmospheric CO2 increased Si accumulation in Brachypodium distachyon grass, yet the patterns of Si deposition in leaves and whether this affects insect herbivore performance remains unknown. Moreover, it is unclear whether CO2 -driven changes in Si accumulation are linked to changes in gas exchange (e.g. transpiration rates). We therefore investigated how pre-industrial (reduced; rCO2 , 200 ppm), ambient (aCO2 , 410 ppm) and elevated (eCO2 , 640 ppm) CO2 concentrations, in combination with Si-treatment (Si+ or Si-), affected Si accumulation in B. distachyon and its subsequent effect on the performance of the global insect pest, Helicoverpa armigera. rCO2 increased Si concentrations by 29% and 36% compared to aCO2 and eCO2 respectively. These changes were not related to observed changes in gas exchange under different CO2 regimes, however. The increased Si accumulation under rCO2 decreased herbivore relative growth rate (RGR) by 120% relative to eCO2, whereas rCO2 caused herbivore RGR to decrease by 26% compared to eCO2 . Si supplementation also increased the density of macrohairs, silica and prickle cells, which was associated with reduced herbivore performance. There was a negative correlation among macrohair density, silica cell density, prickle cell density and herbivore RGR under rCO2 suggesting that these changes in leaf surface morphology were linked to reduced performance under this CO2 regime. To our knowledge, this is the first study to demonstrate that increased Si accumulation under pre-industrial CO2 reduces insect herbivore performance. Contrastingly, we found reduced Si accumulation under higher CO2 , which suggests that some grasses may become more susceptible to insect herbivores under projected climate change scenarios.

Contrasting effects of Miocene and Anthropocene levels of atmospheric CO2 on silicon accumulation in a model grass.

Grasses are hyper-accumulators of silicon (Si), which they acquire from the soil and deposit in tissues to resist environmental stresses. Given the high metabolic costs of herbivore defensive chemicals and structural constituents (e.g. cellulose), grasses may substitute Si for these components when carbon is limited. Indeed, high Si uptake grasses evolved in the Miocene when atmospheric CO2 concentration was much lower than present levels. It is, however, unknown how pre-industrial CO2 concentrations affect Si accumulation in grasses. Using Brachypodium distachyon, we hydroponically manipulated Si-supply (0.0, 0.5, 1, 1.5, 2 mM) and grew plants under Miocene (200 ppm) and Anthropocene levels of CO2 comprising ambient (410 ppm) and elevated (640 ppm) CO2 concentrations. We showed that regardless of Si treatments, the Miocene CO2 levels increased foliar Si concentrations by 47% and 56% relative to plants grown under ambient and elevated CO2, respectively. This is owing to higher accumulation overall, but also the reallocation of Si from the roots into the shoots. Our results suggest that grasses may accumulate high Si concentrations in foliage when carbon is less available (i.e. pre-industrial CO2 levels) but this is likely to decline under future climate change scenarios, potentially leaving grasses more susceptible to environmental stresses.

An extreme heatwave enhanced the xanthophyll de-epoxidation state in leaves of Eucalyptus trees grown in the field.

Heatwaves are becoming more frequent with climate warming and can impact tree growth and reproduction. Eucalyptus parramattensis can cope with an extreme heatwave in the field via transpiratory cooling and enhanced leaf thermal tolerance that protected foliar tissues from photo-inhibition and photo-oxidation during natural midday irradiance. Here, we explored whether changes in foliar carotenoids and/or the xanthophyll cycle state can facilitate leaf acclimation to long-term warming and/or an extreme heatwave event. We found that leaves had similar carotenoid levels when grown for one year under ambient and experimental long-term warming (+ 3 °C) conditions in whole tree chambers. Exposure to a 4-day heatwave (> 43 °C) significantly altered the xanthophyll de-epoxidation state of carotenoids revealing one mechanism by which trees could minimise foliar photo-oxidative damage. The levels of zeaxanthin were significantly higher in both young and old leaves during the heatwave, revealing that violaxanthin de-epoxidation and perhaps de novo zeaxanthin synthesis contributed to enhancement of the xanthophyll cycle state. In a future climate of long-term warming and increased heatwave events, leaves of E. parramattensis will be able to utilise biochemical strategies to alter the xanthophyll cycle state and cope with extreme temperatures under natural solar irradiation.

cis-carotene biosynthesis, evolution and regulation in plants: The emergence of novel signaling metabolites.

Carotenoids are isoprenoid pigments synthesised by plants, algae, photosynthetic bacteria as well as some non-photosynthetic bacteria, fungi and insects. Abundant carotenoids found in nature are synthesised via a linear route from phytoene to lycopene after which the pathway bifurcates into cyclised α- and ß-carotenes. Plants evolved additional steps to generate a diversity of cis-carotene intermediates, which can accumulate in fruits or tissues exposed to an extended period of darkness. Enzymatic or oxidative cleavage, light-mediated photoisomerization and histone modifications can affect cis-carotene accumulation. cis-carotene accumulation has been linked to the production of signaling metabolites that feedback and forward to regulate nuclear gene expression. When cis-carotenes accumulate, plastid biogenesis and operational control can become impaired. Carotenoid derived metabolites and phytohormones such as abscisic acid and strigolactones can fine-tune cellular homeostasis. There is a hunt to identify a novel cis-carotene derived apocarotenoid signal and to elucidate the molecular mechanism by which it facilitates communication between the plastid and nucleus. In this review, we describe the biosynthesis and evolution of cis-carotenes and their links to regulatory switches, as well as highlight how cis-carotene derived apocarotenoid signals might control organelle communication, physiological and developmental processes in response to environmental change.

Leaf-age dependent response of carotenoid accumulation to elevated CO2 in Arabidopsis.

Carotenoids contribute to photosynthesis, photoprotection, phytohormone and apocarotenoid biosynthesis in plants. Carotenoid-derived metabolites control plant growth, development and signalling processes and their accumulation can depend upon changes in the environment. Elevated carbon dioxide (eCO2) often enhances carbon assimilation, early growth patterns and overall plant biomass, and may increase carotenoid accumulation due to higher levels of precursors from isoprenoid biosynthesis. Variable effects of eCO2 on carotenoid accumulation in leaves have been observed for different plant species. Here, we determined whether the variable response of carotenoids to eCO2 was potentially a function of leaf age and the impact of eCO2 on leaf development by growing Arabidopsis in ambient CO2 (400 ppm) and eCO2 (800 ppm). eCO2 increased plant leaf number, rosette area, biomass, seed yield and net photosynthesis. In addition, eCO2 increased carotenoid content by 10-20% in younger emerging leaves, but not in older mature leaves. Older leaves contained approximately 60% less total carotenoids compared to younger leaves. The age-dependent effect on carotenoid content was observed for cotyledon, juvenile and adult phase leaves. We conclude that younger leaves utilize additional carbon from enhanced photosynthesis in eCO2 to increase carotenoid content, yet older leaves have less capacity to store additional carbon into carotenoids.

Periodic root branching in Arabidopsis requires synthesis of an uncharacterized carotenoid derivative.

In plants, continuous formation of lateral roots (LRs) facilitates efficient exploration of the soil environment. Roots can maximize developmental capacity in variable environmental conditions through establishment of sites competent to form LRs. This LR prepattern is established by a periodic oscillation in gene expression near the root tip. The spatial distribution of competent (prebranch) sites results from the interplay between this periodic process and primary root growth; yet, much about this oscillatory process and the formation of prebranch sites remains unknown. We find that disruption of carotenoid biosynthesis results in seedlings with very few LRs. Carotenoids are further required for the output of the LR clock because inhibition of carotenoid synthesis also results in fewer sites competent to form LRs. Genetic analyses and a carotenoid cleavage inhibitor indicate that an apocarotenoid, distinct from abscisic acid or strigolactone, is specifically required for LR formation. Expression of a key carotenoid biosynthesis gene occurs in a spatially specific pattern along the root's axis, suggesting spatial regulation of carotenoid synthesis. These results indicate that developmental prepatterning of LRs requires an uncharacterized carotenoid-derived molecule. We propose that this molecule functions non-cell-autonomously in establishment of the LR prepattern.

Silicon-mediated herbivore defence in a pasture grass under reduced and Anthropocene levels of CO2.

The uptake and accumulation of silicon (Si) in grass plants play a crucial role in alleviating both biotic and abiotic stresses. Si supplementation has been reported to increase activity of defence-related antioxidant enzyme, which helps to reduce oxidative stress caused by reactive oxygen species (ROS) following herbivore attack. Atmospheric CO2 levels are known to affect Si accumulation in grasses; reduced CO2 concentrations increase Si accumulation whereas elevated CO2 concentrations often decrease Si accumulation. This can potentially affect antioxidant enzyme activity and subsequently insect herbivory, but this remains untested. We examined the effects of Si supplementation and herbivory by Helicoverpa armigera on antioxidant enzyme (catalase, CAT; superoxide dismutase, SOD; and ascorbate peroxidase, APX) activity in tall fescue grass (Festuca arundinacea) grown under CO2 concentrations of 200, 410, and 640 ppm representing reduced, ambient, and elevated CO2 levels, respectively. We also quantified foliar Si, carbon (C), and nitrogen (N) concentrations and determined how changes in enzymes and elemental chemistry affected H. armigera relative growth rates and plant consumption. Rising CO2 concentrations increased plant mass and foliar C but decreased foliar N and Si. Si supplementation enhanced APX and SOD activity under the ranging CO2 regimes. Si accumulation and antioxidant enzyme activity were at their highest level under reduced CO2 conditions and their lowest level under future levels of CO2. The latter corresponded with increased herbivore growth rates and plant consumption, suggesting that some grasses could become more susceptible to herbivory under projected CO2 conditions.

Light blocking film in a glasshouse impacts Capsicum annuum L. yield differentially across planting season.

High energy costs are a barrier to producing high-quality produce at protected cropping facilities. A potential solution to mitigate high energy costs is film technology, which blocks heat-producing radiation; however, the alteration of the light environment by these films may impact crop yield and quality. Previous studies have assessed the impact of ULR 80 [i.e., light-blocking film (LBF)] on crop yield and photosynthetically active radiation (PAR); however, an assessment of the spectral environment over different seasons is important to understand potential crop impacts through different developmental phases. In this study, two varieties (red and orange) of Capsicum annuum were grown across two crop cycles: one cycle with primary crop growth in the autumn (i.e., autumn experiment [AE]) and the other with primary crop growth in the summer (i.e., summer experiment [SE]). LBF reduced PAR (roof level: 26%-30%, plant canopy level: 8%-25%) and net radiation (36%-66%). LBF also reduced total diffuse PAR (AE: 8%, SE: 15%), but the diffuse fraction of PAR increased by 7% and 9% for AE and SE, respectively, potentially resulting in differential light penetration throughout the canopy across treatments. LBF reduced near-infrared radiation (700 nm-2,500 nm), including far-red (700 nm-780 nm) at mid- and lower-canopy levels. LBF significantly altered light quantity and quality, which determined the amount of time that the crop grew under light-limited (<12 mol m-2 d-1) versus sufficient light conditions. In AE, crops were established and grown under light-limited conditions for 57% of the growing season, whereas in SE, crops were established and grown under sufficient light conditions for 66% of the growing season. Overall, LBF significantly reduced the yield in SE for both varieties (red: 29%; orange: 16%), but not in AE. The light changes in different seasons in response to LBF suggest that planting time is crucial for maximizing fruit yield when grown under a film that reduces light quantity. LBF may be unsuitable for year-round production of capsicum, and additional development of LBF is required for the film to be beneficial for saving energy during production and sustaining good crop yields in protected cropping.

Novel transcriptome networks are associated with adaptation of capsicum fruit development to a light-blocking glasshouse film.

Light-blocking films (LBFs) can contribute to significant energy savings for protected cropping via altering light transmitting, such as UVA, photosynthetically active radiation, blue and red spectra affecting photosynthesis, and capsicum yield. Here, we investigated the effects of LBF on orange color capsicum (O06614, Capsicum annuum L.) fruit transcriptome at 35 (mature green) and 65 (mature ripe) days after pollination (DAP) relative to untreated control in a high-technology glasshouse. The results of targeted metabolites showed that LBF significantly promotes the percentage of lutein but decreased the percentage of zeaxanthin and neoxanthin only at 35 DAP. At 35 DAP, fruits were less impacted by LBF treatment (versus control) with a total of 1,192 differentially expressed genes (DEGs) compared with that at 65 DAP with 2,654 DEGs. Response to stress and response to light stimulus in biological process of Gene Ontology were found in 65-DAP fruits under LBF vs. control, and clustering analysis revealed a predominant role of light receptors and phytohormone signaling transduction as well as starch and sucrose metabolism in LBF adaptation. The light-signaling DEGs, UV light receptor UVR8, transcription factors phytochrome-interacting factor 4 (PIF4), and an E3 ubiquitin ligase (COP1) were significantly downregulated at 65 DAP. Moreover, key DEGs in starch and sucrose metabolism (SUS, SUC, and INV), carotenoid synthesis (PSY2 and BCH1), ascorbic acid biosynthesis (VTC2, AAO, and GME), abscisic acid (ABA) signaling (NCED3, ABA2, AO4, and PYL2/4), and phenylpropanoid biosynthesis (PAL and DFR) are important for the adaptation of 65-DAP fruits to LBF. Our results provide new candidate genes for improving quality traits of low-light adaptation of capsicum in protected cropping.

Advancing tree genomics to future proof next generation orchard production.

The challenges facing tree orchard production in the coming years will be largely driven by changes in the climate affecting the sustainability of farming practices in specific geographical regions. Identifying key traits that enable tree crops to modify their growth to varying environmental conditions and taking advantage of new crop improvement opportunities and technologies will ensure the tree crop industry remains viable and profitable into the future. In this review article we 1) outline climate and sustainability challenges relevant to horticultural tree crop industries, 2) describe key tree crop traits targeted for improvement in agroecosystem productivity and resilience to environmental change, and 3) discuss existing and emerging genomic technologies that provide opportunities for industries to future proof the next generation of orchards.

Horticultural innovation by viral-induced gene regulation of carotenogenesis.

Multipartite viral vectors provide a simple, inexpensive and effective biotechnological tool to transiently manipulate (i.e. reduce or increase) gene expression in planta and characterise the function of genetic traits. The development of virus-induced gene regulation (VIGR) systems usually involve the targeted silencing or overexpression of genes involved in pigment biosynthesis or degradation in plastids, thereby providing rapid visual assessment of success in establishing RNA- or DNA-based VIGR systems in planta. Carotenoids pigments provide plant tissues with an array of yellow, orange, and pinkish-red colours. VIGR-induced transient manipulation of carotenoid-related gene expression has advanced our understanding of carotenoid biosynthesis, regulation, accumulation and degradation, as well as plastid signalling processes. In this review, we describe mechanisms of VIGR, the importance of carotenoids as visual markers of technology development, and knowledge gained through manipulating carotenogenesis in model plants as well as horticultural crops not always amenable to transgenic approaches. We outline how VIGR can be utilised in plants to fast-track the characterisation of gene function(s), accelerate fruit tree breeding programs, edit genomes, and biofortify plant products enriched in carotenoid micronutrients for horticultural innovation.

Purification and use of carotenoid standards to quantify cis-trans geometrical carotenoid isomers in plant tissues.

Reverse-phase high-performance liquid chromatography (HPLC) is a preferred method used to identify and quantify carotenoids. Here, we describe a straightforward, reliable, and cost-effective protocol to purify and develop individual carotenoid standards for absolute quantification of carotenoids, including selected cis-trans (geometric) isomers. Analytical techniques to extract, purify and collect individual carotenoids using an HPLC system equipped with a Diode Array Detector (DAD) and fraction collector are described. Carotenoids were separated and identified by their characteristic ultraviolet-visible (UV-Vis) absorption spectra and individually isolated based on their retention times using a C30 column. This chapter outlines how to prepare standard calibration curves using known quantities of purified and/or commercially available carotenoids. A series of molar extinction and slope coefficients for phytoene, phytofluene, ζ-carotene, neurosporene, pro-lycopene, all trans-lycopene, lutein, ß-carotene, zeaxanthin, antheraxanthin, violaxanthin, neoxanthin, capsanthin, capsorubin and ß-cryptoxanthin are defined to enable absolute quantification of their abundance in plant, animal, and bacterial tissues. Different approaches for reporting carotenoid abundance by absolute concentration, relative composition, and/or using ratios of different pigments are provided as a convenient resource for carotenoid researchers.

Tangerine tomato roots show increased accumulation of acyclic carotenoids, less abscisic acid, drought sensitivity, and impaired endomycorrhizal colonization.

The Heirloom Golden tangerine tomato fruit variety is highly nutritious due to accumulation of tetra-cis-lycopene, that has a higher bioavailability and recognised health benefits in treating anti-inflammatory diseases compared to all-trans-lycopene isomers found in red tomatoes. We investigated if photoisomerization of tetra-cis-lycopene occurs in roots of the MicroTom tangerine (tangmic) tomato and how this affects root to shoot biomass, mycorrhizal colonization, abscisic acid accumulation, and responses to drought. tangmic plants grown in soil under glasshouse conditions displayed a reduction in height, number of flowers, fruit yield, and root length compared to wild-type (WT). Soil inoculation with Rhizophagus irregularis revealed fewer arbuscules and other fungal structures in the endodermal cells of roots in tangmic relative to WT. The roots of tangmic hyperaccumulated acyclic cis-carotenes, while only trace levels of xanthophylls and abscisic acid were detected. In response to a water deficit, leaves from the tangmic plants displayed a rapid decline in maximum quantum yield of photosystem II compared to WT, indicating a defective root to shoot signalling response to drought. The lack of xanthophylls biosynthesis in tangmic roots reduced abscisic acid levels, thereby likely impairing endomycorrhizal colonisation and drought-induced root to shoot signalling.

Smart Glass Film Reduced Ascorbic Acid in Red and Orange Capsicum Fruit Cultivars without Impacting Shelf Life.

Smart Glass Film (SGF) is a glasshouse covering material designed to permit 80% transmission of photosynthetically active light and block heat-generating solar energy. SGF can reduce crop water and nutrient consumption and improve glasshouse energy use efficiency yet can reduce crop yield. The effect of SGF on the postharvest shelf life of fruits remains unknown. Two capsicum varieties, Red (Gina) and Orange (O06614), were cultivated within a glasshouse covered in SGF to assess fruit quality and shelf life during the winter season. SGF reduced cuticle thickness in the Red cultivar (5%) and decreased ascorbic acid in both cultivars (9-14%) without altering the overall morphology of the mature fruits. The ratio of total soluble solids (TSSs) to titratable acidity (TA) was significantly higher in Red (29%) and Orange (89%) cultivars grown under SGF. The Red fruits had a thicker cuticle that reduced water loss and extended shelf life when compared to the Orange fruits, yet neither water loss nor firmness were impacted by SGF. Reducing the storage temperature to 2 °C and increasing relative humidity to 90% extended the shelf life in both cultivars without evidence of chilling injury. In summary, SGF had minimal impact on fruit development and postharvest traits and did not compromise the shelf life of mature fruits. SGF provides a promising technology to block heat-generating solar radiation energy without affecting fruit ripening and marketable quality of capsicum fruits grown during the winter season.

Short-term exposure to silicon rapidly enhances plant resistance to herbivory.

Silicon (Si) can adversely affect insect herbivores, particularly in plants that evolved the ability to accumulate large quantities of Si. Very rapid herbivore-induced accumulation of Si has recently been demonstrated, but the level of protection against herbivory this affords plants remains unknown. Brachypodium distachyon, a model Si hyperaccumulating grass, was exposed to the chewing herbivore, Helicoverpa armigera, and grown under three conditions: supplied Si over 34 d (+Si), not supplied Si (-Si), or supplied Si once herbivory began (-Si → +Si). We evaluated the effectiveness of each Si treatment at reducing herbivore performance and measured Si-based defenses and phenolics (another form of defense often reduced by Si). Although Si concentrations remained lower, within 72 h of exposure to Si, -Si → +Si plants were as resistant to herbivory as +Si plants. Both +Si and -Si → +Si treatments reduced herbivore damage and growth, and increased mandible wear compared to -Si. After 6 h, herbivory increased filled Si cell density in -Si → +Si plants, and within 24 h, -Si → +Si plants reached similar filled Si cell densities to +Si plants, although decreased phenolics only occurred in +Si plants. We demonstrate that plants with short-term Si exposure can rapidly accumulate Si-based antiherbivore defenses as effectively as plants with long-term exposure.

The 5' untranslated region of the VR-ACS1 mRNA acts as a strong translational enhancer in plants.

The structure and function of untranslated mRNA leader sequences and their role in controlling gene expression remains poorly understood. Previous research has suggested that the 5' untranslated region (5'UTR) of the Vigna radiata aminocyclopropane-1-carboxylate synthase synthase (VR-ACS1) gene may function as a translational enhancer in plants. To test such hypothesis we compared the translation enhancing properties of three different 5'UTRs; those from the VR-ACS1, the chlorophyll a/b binding gene from petunia (Cab22L; a known translational enhancer) and the Vigna radiata pectinacetylesterase gene (PAE; used as control). Identical constructs in which the coding region of the beta-glucuronidase (GUS) gene was fused to each of the three 5'UTRs and placed under the control of the cauliflower mosaic virus 35S promoter were prepared. Transient expression assays in tobacco cell cultures and mung bean leaves showed that the VR-ACS1 and Cab22L 5'UTRs directed higher levels of GUS activity than the PAE 5'UTR. Analysis of transgenic Arabidopsis thaliana seedlings, as well as different tissues from mature plants, confirmed that while transcript levels were equivalent for all constructs, the 5'UTRs from the VR-ACS1 and Cab22L genes can increase GUS activity twofold to fivefold compared to the PAE 5'UTR, therefore confirming the translational enhancing properties of the VR-ACS1 5'UTR.