Search

While most plants die below a threshold of water content, desiccation-tolerant species display specific responses that allow them to survive extreme dehydration. Some of these responses are activated at critical stages during water loss and could represent the difference between desiccation tolerance (DT) and death. Here, we report the development of a simple and reproducible system to determine DT in Selaginella species. The system is based on exposure of excised tissue to a dehydration agent inside small containers, and subsequent evaluation for tissue viability. We evaluated several methodologies to determine viability upon desiccation including: triphenyltetrazolium chloride (TTC) staining, the quantum efficiency of PSII, antioxidant potential, and relative electrolyte leakage. Our results show that the TTC test is a simple and accurate assay to identify novel desiccation-tolerant Selaginella species, and can also indicate viability in other desiccation-tolerant models (i.e. ferns and mosses). The system we developed is particularly useful to identify critical points during the dehydration process. We found that a desiccation-sensitive Selaginella species shows a change in viability when dehydrated to 40% relative water content, indicating the onset of a critical condition at this water content. Comparative studies at critical stages could provide a better understanding of DT mechanisms and unravel insights into the key responses to survive desiccation.

Cucurbita foetidissima and C. radicans are scarcely studied wild pumpkin species that grow in arid and semi-arid areas of Mexico and the United States. This study describes the morphological, proximal composition, metabolic finger-prints and seed protein profiles of C. foetidissima and C. radicans fruits collected in the wild during a one-year period in different locations of central-western Mexico. The results obtained complement the limited information concerning the fruit composition of C. foetidissima and greatly expand information in this respect regarding C. radicans. Morphology and proximal composition of their fruits varied significantly. Different metabolic fingerprints and seed protein profiles were detected between them and also with the chemical composition of domesticated Cucurbita fruits. The neutral lipids in seed, pulp and peels were rich in wax content and in unsaturated compounds, probably carotenoids and tocopherols, in addition to tri-, di- and mono-acylglycerols. The tri- and diacylglycerol profiles of their seed oils were different from commercial seed oils and between each other. They also showed unusual fatty acid compositions. Evidence of a possible alkaloid in the pulp and peel of both species was obtained in addition to several putative cucurbitacins. An abundance of phenolic acids was found in all fruit parts, whereas flavonoids were only detected in the peels. Unlike most cucurbits, globulins were not the main protein fraction in the seeds of C. radicans, whereas the non-structural carbohydrate and raffinose oligosaccharide content in their fruit parts was lower than in other wild cucurbit species. These results emphasize the significantly different chemical composition of these two marginally studied Cucurbita species, which was more discrepant in C. radicans, despite the notion regarding C. foetidissima as an aberrant species with no affinity to any other Cucurbita species.

The Physalis genus includes species of commercial importance due to their ornamental, edible and medicinal properties. These qualities stem from their variety of biologically active compounds. We performed a metabolomic analysis of three Physalis species, i.e., P. angulata, P. grisea, and P. philadelphica, differing in domestication stage and cultivation practices, to determine the degree of inter-species metabolite variation and to test the hypothesis that these related species mount a common metabolomic response to foliar damage caused by Trichoplusia ni larvae. The results indicated that the metabolomic differences detected in the leaves of these species were species-specific and remained even after T. ni herbivory. They also show that each Physalis species displayed a unique response to insect herbivory. This study highlighted the metabolite variation present in Physalis spp. and the persistence of this variability when faced with biotic stressors. Furthermore, it sets an experimental precedent from which highly species-specific metabolites could be identified and subsequently used for plant breeding programs designed to increase insect resistance in Physalis and related plant species.

Increased resistance to insect herbivory in grain amaranth plants is associated with increased betalain pigmentation, either naturally acquired or accumulated in response to blue-red light irradiation . Betalains are water-soluble pigments characteristic of plants of the Caryophyllales order. Their abiotic stress-induced accumulation is believed to protect against oxidative damage, while their defensive function against biotic aggressors is scarce. A previous observation of induced betalain-biosynthetic gene expression in stressed grain amaranth plants led to the proposal that these pigments play a defensive role against insect herbivory. This study provided further support for this premise. First, a comparison of “green” and “red” Amaranthus cruentus phenotypes showed that the latter suffered less insect herbivory damage. Coincidentally, growth and vitality of Manduca sexta larvae were more severely affected when fed on red-leafed A. cruentus plants or on an artificial diet supplemented with red-leaf pigment extracts. Second, the exposure of A. cruentus and A. caudatus plants, having contrasting pigmentation phenotypes, to light enriched in the blue and red wavelength spectra led to pigment accumulation throughout the plant and to increased resistance to insect herbivory. These events were accompanied by the induced expression of known betalain-biosynthetic genes, including uncharacterized DODA genes believed to participate in this biosynthetic pathway in a still undefined way. Finally, transient co-expression of different combinations of betalain-biosynthetic genes in Nicotiana benthamiana led to detectable accumulation of betalamic acid and betanidin. This outcome supported the participation of certain AhDODA and other genes in the grain amaranth betalain-biosynthetic pathway.

El cempasúchil (Tagetes erecta) es una planta asterácea comúnmente utilizada como flor ornamental y ceremonial durante la temporada de otoño en México. Las plantas de cempasúchil cultivadas en el campo presentaron síntomas de la enfermedad de la mancha foliar bacteriana. Se aisló una cepa bacteriana que potencialmente causa la enfermedad de las manchas. El objetivo principal de esta investigación fue clasificar esta bacteria y evaluar su patogenicidad en cempasúchil y otras especies vegetales. El perfil bioquímico identificó esta cepa como Pseudomonas syringae LF2012. El análisis filogenético del gen ARNr 16S reveló una estrecha relación con genomoespecies de Pseudomonas. El perfil de macrorestricción I-CeuI del cromosoma confirmó su alto grado de similitud con distintos patovares de P. syringae. P. syringae LF2012 causa la enfermedad de las manchas cuando se inocula por aspersión en hojas de cempasúchil. Los ensayos de infección de plantas de otras familias (Asteraceae, Brassicaceae, Amaranthaceae, Poaceae y Solanaceae) sugirieron que la enfermedad podría limitarse al cempasúchil. Además, esta cepa provoca respuestas de tipo hipersensible en hojas de Nicotiana tabacum.

Systemin is a peptide hormone that regulates the wound response in tomato plants. Consequently, the overexpression of its prosystemin (ProSys) precursor protein leads to a resource-demanding constitutive activation of tomato’s wound-response. According to the growth vs. defense resource allocation premise, ProSys overexpression should negatively affect the physiological fitness of tomato plants. The present study was performed to explore why the opposite effect was steadily observed, instead. It was based on the premise that a better understanding of this unexpected outcome could help establish improved wound and related defense responses without negatively affecting crop productivity. To this effect, an experimental strategy was deployed to measure various physiological, biochemical and molecular parameters associated with either development, productivity, defense or in combination in untransformed (WT) and ProSys overexpressing (ProSys-OE) tomato plants. Thus, the chlorophyll fluorescence data obtained from plants grown under greenhouse experiments indicated that photosynthetic performance was not affected in ProSys-OE plants which also grew 7–14% taller than WT plants. Moreover, they showed accelerated flowering and yielded fruits of increased size (7–16% taller and wider) and weight (16–58% heavier), with modified fruit quality in terms of firmness (28% higher), titratable acidity (27–32% higher) and chemical composition. These findings suggest two complementary possibilities: (i) systemin is able to modulate both the wound response and plant development through the activation of jasmonic acid biosynthesis and signaling, and (ii) ProSys, an intrinsically disordered protein, acts as a signaling hub to regulate development and defense programs. These results shed light on the understanding of this plant regulatory mechanism and further suggest that systemin/ProSys-based regulation is central to control the defense-development balance in tomato. This knowledge could eventually lead to improved and more environmentally sound agricultural production practices.

Defoliation tolerance (DT) in Amaranthus cruentus is known to reach its apex at the panicle emergence (PE) phase and to decline to minimal levels at flowering (FL). In this study, defoliation-induced changes were recorded in the content of non-structural carbohydrates and raffinose family oligosaccharides (RFOs), and in the expression and/or activity of sugar starvation response-associated genes in plants defoliated at different vegetative and reproductive stages. This strategy identified sugar-starvation-related factors that explained the opposite DT observed at these key developmental stages. Peak DT at PE was associated with increased cytosolic invertase (CI) activity in all organs and with the extensive induction of various class II trehalose-phosphate synthase (TPS) genes. Contrariwise, least DT at FL coincided with a sharp depletion of starch reserves and with sucrose (Suc) accumulation, in leaves and stems, the latter of which was consistent with very low levels of CI and vacuolar invertase activities that were not further modified by defoliation. Increased Suc suggested growth-inhibiting conditions associated with altered cytosolic Suc-to-hexose ratios in plants defoliated at FL. Augmented cell wall invertase activity in leaves and roots, probably acting in a regulatory rather than hydrolytic role, was also associated with minimal DT observed at FL. The widespread contrast in gene expression patterns in panicles also matched the opposite DT observed at PE and FL. These results reinforce the concept that a localized sugar starvation response caused by C partitioning is crucial for DT in grain amaranth.

Background In contrast to commercial Diospyros species, Mesoamerican fruit-producing species are scarcely known, particularly wild species that might harbor desirable traits suitable for breeding. Thus, metabolomic, chemical, and antioxidant profiles of fruits harvested from cultivated Diospyros digyna and wild Diospyros rekoi trees during consecutive winter seasons were obtained. Fruits were harvested in habitats having marked differences in soil quality, climate, and luminosity. Results D. digyna fruits were larger and less acid than D. rekoi fruits, whereas antioxidant activity tended to be higher in D. rekoi fruits. Phenolic, flavonoid, and sugar contents also varied significantly between species. Metabolomic analysis allowed the pre-identification of 519 and 1665 metabolites in negative and positive electrospray ionization (ESI) modes, respectively. Principal component analysis of the positive ESI data explained 51.8% of the variance and indicated clear metabolomic differences between D. rekoi and D. digyna fruits that were confirmed by direct-injection ESI mass spectrometry profiles. Twenty-one discriminating metabolites were detected in fruits of both species; D. digyna fruits differentially accumulated lysophospholipids, whereas discriminating metabolites in D. rekoi fruits were chemically more diverse than those in D. digyna fruits. Conclusion Domesticated D. digyna fruits have improved physicochemical fruit traits compared with wild D. rekoi fruits, including larger size and lower acidity. The metabolomic and chemical composition of their respective fruits were also significantly different, which in D. rekoi was manifested as a notable season-dependent increase in antioxidant capacity. Therefore, wild D. rekoi can be considered as an important genetic resource for the improvement of commercial Diospyros fruit quality. © 2019 Society of Chemical Industry.

Plants can tolerate some degree of dehydration but below a threshold of water content most plants die. However, some species display specific physiological, biochemical, and molecular responses that allow survival to desiccation. Some of these responses are activated at critical stages during water loss and could represent the difference between desiccation tolerance (DT) and death. Here, we report the development of a simple and reproducible system to determine DT in Selaginella species. This system is based on the use of excised tissue (explants), exposed to a dehydration agent inside small containers, rather than whole plants making it faster, better controlled, and potential use under field conditions. We also report that the triphenyltetrazolium chloride test is a simple and accurate assay to determine tissue viability. The explant system is particularly useful to identify critical points during the dehydration process and was applied to identify novel desiccation-tolerant Selaginella species. Our data suggest that desiccation-sensitive Selaginella species have a change in viability when dehydrated to 40% RWC, indicating the onset of a critical condition at this water content. Comparative studies at these critical stages could provide a better understanding of DT mechanisms and unravel insights into the key responses to survive desiccation.HighlightIn this article, we developed a simple and efficient system to determine desiccation tolerance and critical stages during the dehydration process in Selaginella that can be applied to other plant species.

Taxonomically restricted genes, or TRGs, are specific to a particular taxon that can be found only in the genomes of single species or are represented as orthologs in closely related genera. Despite being regarded with a mixture of skepticism and awe by the scientific community, progress has been gradually attained in the understanding of their presumed origin and function in most, if not all, forms of life. Grain amaranth is not an exception, as shown by the numerous unknown function TRGs that were unveiled by a recent transcriptomic analysis undergone under different (a)biotic stress conditions. True to their nature, amaranth TRGs appear to be mostly stress-related genes that may offer a clue to better understand the ability of these remarkable plants to thrive under unfavorable ambient conditions. This chapter will concentrate on the description of what has gradually emerged from the incipient study of TRGs in grain amaranth and will place this knowledge in the context of what is known about these enigmatic genes in other organisms.

Genetic transformation of grain amaranth has been a challenging enterprise due to its notorious recalcitrance to Agrobacterium-mediated transformation processes. This chapter will describe the relatively small number of studies, most of them involving leafy amaranths, that have been successful in overcoming this natural limitation. It will also describe the use of the up to now ineffectual alternative genetic transformation methods. A focus on recent findings that promise to be the breakthrough required to permit the straightforward genetic transformation of grain amaranths will close this chapter in a positive note. This development will represent a powerful experimental tool to achieve the full agronomic potential of this environmentally resilient crop.

Bioremediation is an environmentally sound and cost-effective strategy to restore soils contaminated with petroleum oil. In this study, native bio-surfactant-producing bacteria able to use polycyclic aromatic hydrocarbons (PAHs: anthracene [ANT] or phenanthrene [PHE]) as their sole carbon source were isolated from soil contaminated with weathered petroleum oil (WPO) collected near “La Venta” gas processing complex, in Tabasco, Mexico. Bacteria able to grow in 200 ppm of ANT or PHE and having high bio-surfactant activity were selected. Included were bacteria identified as Sphingobium sp., Bosea sp., Pseudomonas sp., Rhodococcus sp. and Phenylobacterium sp. Different consortia of these bacteria ± bio-stimulation with glucose, ammonium nitrate, or both, were examined for their capacity to degrade either WPO or fresh crude petroleum oil (FCPO) in soil microcosms. No efficient short-term (24 days) degradation of WPO using bio-augmentation and bio-stimulation strategies was possible using two bacterial consortia conformed by combinations of these bacterial isolates. Best results were obtained with a consortium composed of Pseudomonas cloritidismutans and Rhodococcus qingshengii, identified by 16S rRNA sequencing, which led to an 86% reduction of FCPO contaminants in soil microcosms, 90 days after treatment. However, the bioremediation efficiency of this consortium was significantly reduced by moderate salinity levels in the soil. Although promising, these results highlight the adverse effect that weathering and/or salinity may have on the remediation of petroleum oil-contaminated soils.

The effect of short-term treatments with non-toxic concentrations of chemical elicitors of carbon mobilization and/or defense responses on fructan accumulation and complexity was analyzed in Agave tequilana plantlets. These included sucrose (ExSuc), salicylic acid (SA), and methyl jasmonate (MeJA). Methyl viologen (MV), an oxidative-stress elicitor, was also tested. Stems of ExSuc- and SA-treated agaves accumulated fructan with contrasting degree of polymerization (DP), being higher (DP12) in the ExSuc treatment. The difference agreed with 1-SST, 6G-FFT and 6-fructan exohydrolase (FEH) gene expression patterns. Thus, a strong, 6G-FFT expression detected 6 days after treatment (DAT), coupled to a systematic repression of FEH genes occurred in Ex-Suc treated agaves. Conversely, SA treatment induced maximum 6G-FFT expression and a transitory induction of FEH genes 2 DAT. MV also induced an accumulation of low-DP fructans 6 DAT. Additionally, it stimulated the highest fructan accumulation in leaves. Contrariwise, MeJA led to a depletion of soluble non-structural carbohydrates (NSCs) and fructan, particularly in leaves. An inverse relationship between high invertase and FEH gene expression levels and minimal NSCs and fructan reserves was observed in response to MeJA. Low DP fructan accumulation by MV could not be attributed to a measurable oxidative stress. Still, high antioxidant enzyme activity, indirectly manifesting oxidative stress, coincided with fructan accumulation in MV-treated agaves. High invertase and FEH expression levels induced by MeJA in leaves, and to a lesser degree by SA and MV, coincided with transcript accumulation of defense-related genes, and were, to a certain extent, in accordance with the “sweet immunity” concept, linking sugar and defense signaling.

Water deficit stress (WDS)-tolerance in grain amaranths (Amaranthus hypochondriacus, A. cruentus and A. caudatus), and A. hybridus, their presumed shared ancestor, was examined. A. hypochondriacus was the most WDS-tolerant species, a trait that correlated with an enhanced osmotic adjustment (OA), a stronger expression of abscisic acid (ABA) marker genes and a more robust sugar starvation response (SSR). Superior OA was supported by higher basal hexose (Hex) levels and high Hex/sucrose (Suc) ratios in A. hypochondriacus roots, which were further increased during WDS. This coincided with increased invertase, amylase and sucrose synthase activities and a strong depletion of the starch reserves in leaves and roots. The OA was complemented by the higher accumulation of proline, raffinose, and other probable raffinose-family oligosaccharides of unknown structure in leaves and/or roots. The latter coincided with a stronger expression of Galactinol synthase 1 and Raffinose synthase in leaves. Increased SnRK1 activity and expression levels of the class II AhTPS9 and AhTPS11 trehalose phosphate synthase genes, recognized as part of the SSR network in Arabidopsis, were induced in roots of stressed A. hypochondriacus. It is concluded that these physiological modifications improved WDS in A. hypochondriacus by raising its water use efficiency.

A previous study with spr2 mutant tomato plants which are negatively affected in the synthesis of jasmonic acid (JA), suggested that JA regulates the arbuscular mycorrhizal fungi (AMF) colonization via the control of carbon (C) partitioning. Although this and other studies have suggested the important positive role played by JA in the regulation of AMF root colonization in tomato plants, it is currently unclear how different host plant genetic backgrounds affect gene expression and secondary metabolites variation during JA-dependent mycorrhization. In this study, wild type and spr2 mutant tomato plants having “low”, “medium” and “high” mycorrhizal colonization with Rhizophagus irregularis, were analyzed independently using transcriptomic and untargeted metabolomic approaches. The results obtained revealed that the degree of mycorrhizal colonization efficiency could be associated with contrasting expression levels of certain key genes controlling gibberellin signaling, ethylene biosynthesis and signaling, and synthesis of apocarotenoids, phenylpropanoids and tomatine, in roots. Only a few wound responsive genes, including JA signaling and biosynthesis genes, such as Prosystemin and JAZ2 were found to influence AMF colonization. Conversely, a systemic and JA-dependent induction/ repression of genes different from those altered in roots was detected in leaves of mycorrhizal plants. The most significant changes in metabolite abundance were detected in roots with reduced AMF colonization. Included among the latter were metabolites known to be associated with important aspects of AMF symbiosis, such as signaling, nutrient exchange and modulation of pathogen defense response. Αlpha-tomatine levels appeared to be an important factor, whose abundance negatively correlated wit h AMF colonization levels in tomato, suggesting a regulatory role for JA in the synthesis of this metabolite during the AMF symbiosis.

Arbuscular mycorrhizal fungi (AMF) colonization, sampled at 32–50 days post-inoculation (dpi), was significantly reduced insuppressor of prosystemin-mediated responses2 (spr2)mutant tomato plants impaired in the ω−3FATTY ACID DESATURASE7(FAD7) gene that limits the generation of linolenic acid and, consequently, the wound-responsive jasmonic acid (JA) burst. Contrary to wild-type (WT) plants, JA levels in root and leaves ofspr2mutants remained unchanged in response to AMF colonization, further supporting its regulatory role in the AM symbiosis. Decreased AMF colonization inspr2plants was also linked to alterations associated with a disrupted FAD7 function, such as enhanced salicylic acid (SA) levels and SA-related defense gene expression and a reduction in fatty acid content in both mycorrhizalspr2roots and leaves. Transcriptomic data revealed that lower mycorrhizal colonization efficiency inspr2mutants coincided with the modified expression of key genes controlling gibberellin and ethylene signaling, brassinosteroid, ethylene, apocarotenoid and phenylpropanoid synthesis, and the wound response. Targeted metabolomic analysis, performed at 45 dpi, revealed augmented contents of L-threonic acid and DL-malic acid in colonizedspr2roots which suggested unfavorable conditions for AMF colonization. Additionally, time- and genotype-dependent changes in root steroid glycoalkaloid levels, including tomatine, suggested that these metabolites might positively regulate the AM symbiosis in tomato. Untargeted metabolomic analysis demonstrated that the tomato root metabolomes were distinctly affected by genotype, mycorrhizal colonization and colonization time. In conclusion, reduced AMF colonization efficiency inspr2mutants is probably caused by multiple and interconnected JA-dependent and independent gene expression and metabolomic alterations.

Jasmonic acid (JA) is a phytohormone involved in plant development and defense. A major role of JA is the enhancement of secondary metabolite production, such as response to herbivory. Systemin is a bioactive plant peptide of 18 amino acids that contributes to the induction of local and systemic defense responses in tomato (Solanum lycopersicum) through JA biosynthesis. The overexpression of systemin (PS-OE) results in constitutive JA accumulation and enhances pest resistance in plants. Conversely, mutant plants affected in linolenic acid synthesis (spr2) are negatively compromised in the production of JA which favors damage and oviposition by insect herbivores. With undirected mass fingerprinting analyses, we found global metabolic differences between genotypes with modified jasmonic acid production. The spr2 mutants were enriched in di-unsaturated fatty acids and generally showed more changes. The PS-OE genotype produced an unidentified compound with a mass-to-charge ratio of 695 (MZ695). Most strikingly, the steroidal glycoalkaloid biosynthesis was negatively affected in the spr2 genotype. Complementation with jasmonic acid could restore the tomatine pathway, which strongly suggests the control of steroidal glycoalkaloid biosynthesis by jasmonic acid. spr2 plants were more susceptible to fungal infection with Fusarium oxysporum f.sp. ciceris, but not to bacterial infection with Clavibacter michiganensis subsp. michiganensis which supports the involvement of steroidal glycoalkaloids in the plant response against fungi.

Nuclear factor-Y (NF-Y), is a plant heterotrimeric transcription factor constituted by NF-YA, NF-YB and NF-YC subunits. The function of many NF-Y subunits, mostly of the A and B type, has been studied in plants, but knowledge regarding the C subunit remains fragmentary. Here, a water stress-induced NF-YC gene from Amaranthus hypochondriacus (AhNF-YC) was further characterized by its overexpression in transgenic Arabidospis thaliana plants. A role in development was inferred from modified growth rates in root, rosettes and inflorescences recorded in AhNF-YC overexpressing Arabidopsis plants, in addition to a delayed onset of flowering. Also, the overexpression of AhNF-YC caused increased seedling sensitivity to abscisic acid (ABA), and influenced the expression of several genes involved in secondary metabolism, development and ABA-related responses. An altered expression of the latter in water stressed and recovered transgenic plants, together with the observed increase in ABA sensitivity, suggested that their increased water stress resistance was partly ABA-dependent. An untargeted metabolomic analysis also revealed an altered metabolite pattern, both in normal and water stress/recovery conditions. These results suggest that AhNF-YC may play an important regulatory role in both development and stress, and represents a candidate gene for the engineering of abiotic stress resistance in commercial crops.

A novel strain of Pectobacterium, isolated from infected sunflower plants (Helianthus annuus L.) in Mexico was characterized. Inoculated sunflower plants developed both tissue chlorosis and soft-rot on leaves. The broad host range shown by this pathogen, which included members of the Agavaceae, Asteraceae, Brassicaceae and Solanaceae, was characteristic of the genus Pectobacterium. The metabolic profile and molecular data, in addition to the secretion of plant-cell-wall-degrading enzymes, confirmed its identification as a member of the Pectobacterium genus. A phylogenetic tree constructed on the basis of its 16S rDNA sequence revealed a high identity (98 %) with P. cacticidum. Amplification and restriction-fragment-length-polymorphism analysis of internal transcribed sequences further confirmed its classification as P. cacticidum. Similar to strains of P. atrosepticum, P. carotovorum and Dickeya spp., the new P. cacticidum strain FHLGJ22 has a coronafacic ligase gene and produces coronatine, a virulence factor usually associated with phytopathogenic strains of Pseudomonas syringae. Our results suggest that this strain may utilize a dual infection process involving cell maceration and plant toxins, which is synchronized via an unknown mechanism, might confer an adaptive advantage to colonize different plant hosts.

This study was performed to test the working hypothesis that the primary determinants influencing seasonal driven modifications in carbon mobilization and other key biochemical parameters in leaves of poorly known Diospyros digyna (Ddg; semi-domesticated; perennial) and D. rekoi (Dre; undomesticated; deciduous) trees are determined by environmental growing conditions, agronomic management and physiological plasticity. Thus, biochemical changes in leaves of both trees were recorded seasonally during two successive fruiting years. Trees were randomly sampled in Western Mexico habitats with differing soil quality, climatic conditions, luminosity, and cultivation practices. Leaves of Ddg had consistently higher total chlorophyll contents (CT) that, unexpectedly, peaked in the winter of 2015. In Dre, the highest leaf CT values recorded in the summer of 2015 inversely correlated with low average luminosity and high Chl a/ Chlb ratios. The seasonal CT variations in Dre were congruent with varying luminosity, whereas those in Ddg were probably affected by other factors, such as fluctuating leaf protein contents and the funneling of light energy to foliar non-structural carbohydrates (NSCs) accumulation, which were consistently higher than those detected in Dre leaves. Seasonal foliar NSC fluctuations in both species were in agreement with the carbon (C) demands of flowering, fruiting and/ or leaf regrowth. Seasonal changes in foliar hexose to sucrose (Hex/ Suc) ratios coincided with cell wall invertase activity in both species. In Dre, high Hex/ Suc ratios in spring leaves possibly allowed an accumulation of phenolic acids, not observed in Ddg. The above results supported the hypothesis proposed by showing that leaf responses to changing environmental conditions differ in perennial and deciduous Diospyros trees, including a dynamic adjustment of NSCs to supply the C demands imposed by reproduction, leaf regrowth and, possibly, stress.

In this study, water deficit stress (WDS)-tolerance in several cultivars of grain amaranth species (Amaranthus hypochondriacus[Ahypo],A. cruentus[Acru] and A.caudatus[Acau]), in addition toA. hybridus(Ahyb), an ancestral amaranth, was examined. Ahypo was the most WDS-tolerant species, whereas Acau and Ahyb were WDS-sensitive. Data revealed that the differential WDS tolerance observed was multifactorial. It involved increased proline and raffinose (Raf) in leaves and/ or roots. Higher foliar Raf coincided with inducedGalactinol synthase 1(AhGolS1) andRaffinose synthase(AhRafS) expression. Unknown compounds, possibly larger RFOs, also accumulated in leaves of WDS-tolerant amaranths, which had high Raf/ Verbascose ratios. Distinct nonstructural carbohydrate (NSC) accumulation patterns were observed in tolerant species under WDS and recovery, such as: i) high Hex/ Suc ratios in roots coupled to increased cell wall and vacuolar invertase and sucrose synthase activities; ii) a severer depletion of starch reserves; iii) lower NSC content in leaves, and iv) higher basal hexose levels in roots which further increased under WDS. WDS-marker gene expression patterns proposed a link between amaranth’s WDS tolerance and abscisic acid-dependent signaling. Results obtained also suggest thatAhTRE,AhTPS9,AhTPS11,AhGolS1 and AhRafSare reliable gene markers of WDS tolerance in amaranth.HighlightDifferential water deficit stress tolerance in grain amaranths and their ancestor,Amaranthus hybridus, is a multifactorial process involving various biochemical changes and modified expression patterns of key stress-related genes.

The expression of genes coding for sucrose:sucrose 1-fructosyltransferase (1-SST; EC 2.4.1.99) and fructan:fructan 1-fructosyltransferase (1-FFT; EC 2.4.1.100), both fructan biosynthesizing enzymes, characterization by TLC and HPAEC-PAD, as well as the quantification of the fructo-oligosaccharides (FOS) accumulating in response to the exogenous application of sucrose, kinetin (cytokinin) or other plant hormones associated with (a)biotic stress responses were determined in two Agave species grown in vitro, domesticated Agave tequilana var. azul and wild A. inaequidens. It was found that elicitors such as salicylic acid (SA), and jasmonic acid methyl ester (MeJA) had the strongest effect on fructo-oligosaccharide (FOS) accumulation. The exogenous application of 1mM SA induced a 36-fold accumulation of FOS of various degrees of polymerization (DP) in stems of A. tequilana. Other treatments, such as 50mM abscisic acid (ABA), 8% Sucrose (Suc), and 1.0 mg L(-1) kinetin (KIN) also led to a significant accumulation of low and high DP FOS in this species. Conversely, treatment with 200 μM MeJA, which was toxic to A. tequilana, induced an 85-fold accumulation of FOS in the stems of A. inaequidens. Significant FOS accumulation in this species also occurred in response to treatments with 1mM SA, 8% Suc, and 10% polyethylene glycol (PEG). Maximum yields of 13.6 and 8.9 mg FOS per g FW were obtained in stems of A. tequilana and A. inaequidens, respectively. FOS accumulation in the above treatments was tightly associated with increased expression levels of either the 1-FFT or the 1-SST gene in tissues of both Agave species.

Several reports have shown that crude or purified extracts of green, brown, and red seaweeds induce protection against fungal, bacterial, and viral pathogens in plants. In this work, we report that polysaccharide-enriched seaweed extracts obtained from green, Ulva lactuca and Caulerpa sertularioides, and brown algae, Padina gymnospora and Sargassum liebmannii, induced protection against the necrotrophic fungus Alternaria solani in tomato plants (Solanum lycopersicum). Protein activity of defense-related proteins polyphenol oxidase, guaiacol peroxidase and proteinase inhibitors together with expression levels of systemic wound response (SWRP) genes were also measured in leaf samples after algal extract treatment. All extracts were shown to reduce necrotic lesions induced by A. solani, particularly those obtained from U. lactuca and P. gymnospora. U. lactuca extracts induced the expression of SWRP genes, including defense, signal pathway, and protease genes, whereas those obtained from C. sertularioides, P. gymnospora and S. liebmannii showed almost no induction of SWRP genes, suggesting that extracts from the latter, whose carbohydrate composition varied from that of U. lactuca, may act through mechanisms other than the jasmonic acid/systemin wound-response pathway.

Inoculation of mango trees with Burkholderia caribensis XV and Rhizobium sp. XXV led to mango growth promotion (dry biomass increased in root 89 %, stem 34 %, leaves 51 %, and foliar area 53 %), floral fate (floral buds 100 %), and increased number of flowers (100 %). Nitrogen content in leaves was similar in inoculated and noninoculated trees, around 1.4 % (optimal condition for floral induction). The total foliar nitrogen content increased significantly (56 %) when the microbial inoculation treatment was applied. In addition, the initial content of sucrose, glucose, and fructose in leaves was higher in the microbial inoculation treatment trees but decreased during the evaluated period. The sucrose content in the noninoculated trees presented similar dynamics compared to the microbial inoculation treatment trees, but glucose and fructose showed increased values compared to those of the microbial inoculation treatment. FLOWERING LOCUS T (FT) expression profiles normalized to ACTIN showed similar dynamics but different expression levels: RQ values of 0.03 and 0.05 for noninoculated and microbial inoculation treatments, respectively. In addition, FT expression profiles in microbial inoculation, normalized to the noninoculated treatment, showed an increased FT expression dynamic over time (up to RQ = 2.2), although a drastic decrease in the last sampling date, when all trees presented developed panicles and flowers, was observed. This FT upregulation was in accordance with the flowering induction in that treatment. Temperature had an important influence on mango flowering induction, which was observed for a 1-month period (~10 °C at night and 20 °C during the day). Bud growth that occurred during that period generated mixed and floral buds depending on the exposure time to these inductive temperatures, less than 2 weeks and more than 3 weeks, respectively. Data indicate that inoculation of mango trees with plant growth-promoting rhizobacteria (associated with this crop) is a potential alternative way to promote growth and induce flowering in mango, greatly reducing the high economical costs and environmental contamination associated with traditional agricultural practices.

Twenty isolates of Trichoderma were obtained from orchards located in three main mango-producing States in Mexico: Chiapas, Oaxaca, and Michoacan, which represent different agronomical management practices and levels of soil fertility. Phylogenetic analysis showed that Trichoderma isolates belong to the following taxa: Hypocrea lixii (10 isolates), Hypocrea jecorina (four isolates), Trichoderma asperellum (three isolates), Trichoderma spirale (two isolates), and Trichoderma brevicompactum (one isolate). The genus Hypocrea is the teleomorph (sexual) stage of the genus Trichoderma, anamorph stage. Seventeen Trichoderma isolates showed at least 67% growth inhibition against the phytopathogenic fungus Colletotrichum gloeosporioides ATCC MYA 456 and three Trichoderma isolates showed complete overgrowth of this pathogen. One member of this group, identified as T. asperellum T8a, was able to control C. gloeosporioides ATCC MYA 456 in vitro and in vivo, as well as five C. gloeosporioides isolates obtained from mango orchards from the State of Oaxaca. Assay of the lytic enzymes involved suggest that cellulases of T. asperellum T8a play a role in biological control against C. gloeosporioides ATCC MYA 456 more than chitinase or glucanase. Thus, native T. asperellum T8a associated with mango trees can be used to enhance mango production, controlling anthracnose through cellulase activity.

An amaranth DGR gene, induced under abiotic stress, modifies cell wall structure and causes hypersensitivity to ABA and salt when overexpressed in Arabidopsis. DUF642 is a highly conserved plant-specific family of unknown cell wall-associated proteins. The AhDGR2 gene, coding for a DUF642 protein, was significantly induced in grain amaranth (Amaranthus hypochondriacus) plants subjected to water-deficit and salinity stress, thereby suggesting its participation in abiotic stress tolerance in this plant. A role in development was also inferred from the higher AhDGR2 expression rates detected in young tissues. Subsequent overexpression of AhDGR2 in transgenic Arabidopsis plants (OE-AhDGR2) supported its possible role in development processes. Thus, OE-AhDGR2 plants generated significantly longer roots when grown in normal MS medium. However, they showed a hypersensitivity to increasing concentrations of abscisic acid or NaCl in the medium, as manifested by shorter root length, smaller and slightly chlorotic rosettes, as well as highly reduced germination rates. Contrary to expectations, OE-AhDGR2 plants were intolerant to abiotic stress. Moreover, cell walls in transgenic plants were thinner, in leaves, and more disorganized, in roots, and had significantly modified pectin levels. Lower pectin methylesterase activity detected in leaves of OE-AhDGR2 plants, but not in roots, was contrary to previous reports associating DUF642 proteins and decreased pectin esterification levels in cell walls. Nonetheless, microarray data identified candidate genes whose expression levels explained the phenotypes observed in leaves of OE-AhDGR2 plants, including several involved in cell wall integrity and extension, growth and development, and resistance to abiotic stress. These results support the role of DUF642 proteins in cell wall-related processes and offer novel insights into their possible role(s) in plants.

Two grain amaranth transcription factor (TF) genes were overexpressed in Arabidopsis plants. The first, coding for a group VII ethylene response factor TF (i.e., AhERF-VII) conferred tolerance to water-deficit stress (WS) in transgenic Arabidopsis without affecting vegetative or reproductive growth. A significantly lower water-loss rate in detached leaves coupled to a reduced stomatal opening in leaves of plants subjected to WS was associated with this trait. WS tolerance was also associated with an increased antioxidant enzyme activity and the accumulation of putative stress-related secondary metabolites. However, microarray and GO data did not indicate an obvious correlation between WS tolerance, stomatal closure, and abscisic acid (ABA)-related signaling. This scenario suggested that stomatal closure during WS in these plants involved ABA-independent mechanisms, possibly involving reactive oxygen species (ROS). WS tolerance may have also involved other protective processes, such as those employed for methyl glyoxal detoxification. The second, coding for a class A and cluster I DNA binding with one finger TF (i.e., AhDof-AI) provided salt-stress (SS) tolerance with no evident fitness penalties. The lack of an obvious development-related phenotype contrasted with microarray and GO data showing an enrichment of categories and genes related to developmental processes, particularly flowering. SS tolerance also correlated with increased superoxide dismutase activity but not with augmented stomatal closure. Additionally, microarray and GO data indicated that, contrary to AhERF-VII, SS tolerance conferred by AhDof-AI in Arabidopsis involved ABA-dependent and ABA-independent stress amelioration mechanisms.

Volatile organic compounds (VOCs) emitted from plants in response to insect infestation can function as signals for the attraction of predatory/parasitic insects and/or repulsion of herbivores. VOCs also may play a role in intra- and inter-plant communication. In this work, the kinetics and composition of VOC emissions produced by tomato (Solanum lycopersicum) plants infested with the greenhouse whitefly Trialeurodes vaporariorum was determined within a 14 days period. The VOC emission profiles varied concomitantly with the duration of whitefly infestation. A total of 36 different VOCs were detected during the experiment, 26 of which could be identified: 23 terpenoids, plus decanal, decane, and methyl salicylate (MeSA). Many VOCs were emitted exclusively by infested plants, including MeSA and 10 terpenoids. In general, individual VOC emissions increased as the infestation progressed, particularly at 7 days post-infestation (dpi). Additional tunnel experiments showed that a 3 days exposure to VOC emissions from whitefly-infested plants significantly reduced infection by a biotrophic bacterial pathogen. Infection of VOC-exposed plants induced the expression of a likely tomato homolog of a methyl salicylate esterase gene, which preceded the expression of pathogenesis-related protein genes. This expression pattern correlated with reduced susceptibility in VOC-exposed plants. The observed cross-kingdom effect of plant-plant signaling via VOCs probably represents a generalized defensive response that contributes to increased plant fitness, considering that resistance responses to whiteflies and biotrophic bacterial pathogens in tomato share many common elements.

Tomato systemin is a bioactive peptide that regulates the systemic activation of wound-responsive genes. It is released from its 200 amino acid precursor called prosystemin. Initial tissue-localization and hormone-induced expression assays indicated that the tomato prosystemin gene (SlPS) accumulates mainly in floral tissues and in response to exogenous abscisic acid and methyl jasmonate (MeJA) treatments, respectively. Later, the promoter regions of the PS gene in tomato (Solanum lycopersicum L. cv. Castlemart), pepper (Capsicum annuum) and potato (Solanum tuberosum) were isolated and an in silico analysis of the SlPS promoter revealed an over-representation of stress- and MeJA-responsive motifs. A subsequent 5 � deletion analysis of the SlPS promoter fused to the β-glucuronidase reporter (GUS) gene showed that the -221 to +40 bp proximal SlPS promoter region was sufficient to direct the stigma, vascular bundle-specific and MeJA-responsive expression of GUS in transgenic tobacco plants. Important vascular-tissue-specific, light- and MeJA-responsive cis-elements were also present in this region. These findings provide relevant information regarding the transcriptional regulation mechanisms of the SlPS promoter operating in transgenic tobacco plants. They also suggest that its tissue-specificity and inducible nature could have wide applicability in plant biotechnology.

In a cultivation experiment 18 different Amaranthus genotypes were cultivated in parallel in Argentina, Mexico, Spain and two different locations in the Czech Republic. The ripe seeds were analysed for their content of 11 polyphenols and the variations among genotype, species and location were analysed by principal component analysis (PCA). The flavonoid, rutin, exhibited large variations with varying environmental conditions whereas the flavonoid, nicotiflorin, was affected less. Amaranthus hypochondriacus displayed the most stable content of polyphenols with a high end content of flavonoids. The variations between location/environmental condition were primarily described by the variations in the content of p-coumaric acid and protocatechuic acid in the seed samples.

Transgenic tobacco plants capable of over-expressing Xenopus PPARα (xPPARα), a transcription factor known to be required for peroxisome proliferation in animals, were recently generated. These plants (herewith referred to as PPAR-OE) were found to have increased peroxisome abundance, higher peroxisomal acyl-CoA oxidase and catalase activity and modified fatty acid metabolism. Further characterization of PPAR-OE plants revealed a higher susceptibility to virulent and a partial loss of resistance to avirulent Pseudomonas syringae pathogens, whereas the basal resistance response remained unaffected. Biochemical- and defense-related gene expression analyses showed that increased susceptibility to bacterial invasion coincided with the generalized reduction in H(2)O(2) and salicylic acid (SA) levels observed within the first 24 h of bacterial contact. Decreased H(2)O(2) levels were correlated with modified activity levels of catalase and other antioxidant enzymes. A correspondence between a rapid (within 1-24 hpi; ACCO and AOC) and sustained increase (up to 6 days pi; ACCO) in the expression levels of ethylene (ACCO) and jasmonic acid (AOC) biosynthetic genes and a higher susceptibility to virulent bacterial invasion was also observed in PPAR-OE plants. Conversely, no apparent differences in the short- and/or long-term expression levels of markers for the hypersensitive-response, oxidative burst and systemic-acquired resistance were observed between wild type and PPAR-OE plants. The results suggest that peroxisome proliferation could lead to increased susceptibility to bacterial pathogens in tobacco by altering the redox balance of the plant and the expression pattern of key defense signaling pathway genes.

A suppression-subtractive-hybridization (SSH) strategy led to the identification of several genes whose expression was differentially modified in response to different larval phases present during the infestation process of tomato plants (Solanum lycopersicum) by virus-free whitefly Bemisia tabaci (Bt). The findings regarding photosynthetic gene expression were in accordance to previous studies reporting altered patterns of expression as a result of insect herbivory. However, the examination, in this study, of four stages of larval Bt development permitted the detection of phase-dependent changes in gene expression which appeared to target specific photosynthetic complexes. Thus, an upregulation of photosystem II genes in the latter two phases of Bt development contrasted with a general repression of genes belonging to the three other photosynthetic complexes, in addition to a number of genes coding for proteins associated with the oxygen evolving complex and the Calvin cycle. We propose that the contrasting pattern of expression led to an over-excitation of PSII and consequent oxidative damage, as suggested by the concomitant upregulation of oxidative stress genes, and could have contributed to the wide-spread necrosis observed in Bt-infested tomato plants at late stages of the plant-insect interaction.

A suppression-subtractive-hybridization (SSH) strategy was used to identify genes whose expression was modified in response to virus-free whitefly Bemisia tabaci (Bt, biotype A) infestation in tomato (Solanum lycopersicum) plants. Thus, forward and reverse SSH gene libraries were generated at four points in the whitefly's life cycle, namely at (1) 2 days (adult feeding and oviposition: phase I); (2) 7 days (mobile crawler stage: phase II); (3) 12 days (second to third instar nymphal transition: phase III) and (4) 18 days (fourth instar nymphal stage: phase IV). The 169 genes with altered expression (up and downregulated) that were identified in the eight generated SSH libraries, together with 75 additional genes that were selected on the basis of their involvement in resistance responses against phytofagous insects and pathogens, were printed on a Nexterion(®) Slide MPX 16 to monitor their pattern of expression at the above phases. The results indicated that Bt infestation in tomato led to distinctive phase-specific expression/repression patterns of several genes associated predominantly with photosynthesis, senescence, secondary metabolism and (a)biotic stress. Most of the gene expression modifications were detected in phase III, coinciding with intense larval feeding, whereas fewer changes were detected in phases I and IV. These results complement previously reported gene expression profiles in Bt-infested tomato and Arabidopisis, and support and expand the opinion that Bt infestation leads to the downregulation of specific defense responses in addition to those controlled by jasmonic acid.

Mexico is considered to be one of the centers of origin of grain amaranth species. Recently, plants with abnormal anatomical features were observed in experimental fields established in Central Mexico. The most noticeable symptoms, which consisted of excessive stem and bud proliferation, mosaics and unusual coloration, suggested that they might be phytoplasma-induced disorders. Thus, different accessions of grain amaranth (Amaranthus hypochondriacus and A. cruentus) plants were subjected to polymerase chain reaction (PCR) analysis specifically designed to detect these pathogens. Two universal phytoplasma-specific primer pairs were tested in a nested PCR assay, with primer pair P1/tint (followed by primer pair R16F2/R16R2). Further DNA sequencing analysis of the resulting amplicons indicated that these phytoplasmas may be related to others already affecting important agricultural crops in Mexico, such as soybean. Data are presented that disclose the etiology of these syndromes by the use of molecular techniques. To the best of our knowledge, this finding constitutes the first report of a phytoplasma-related disease in grain amaranth.

The role of jasmonic acid (JA) on mycorrhizal colonization by Glomus fasciculatum in tomato plants was examined using mutant plants overexpressing prosystemin (PS) or affected in the synthesis of JA (suppressor of prosystemin-mediated responses 2, spr2). The degree of mycorrhizal colonization was determined by measuring frequency (F%) and intensity (M%) of colonization and arbuscule abundance (A%). Gene expression and biochemical analyses were also performed in roots to detect changes in carbon (C) partitioning. Colonization was similar in mycorrhizal PS and wild-type roots, except for a higher A% in the former. Conversely, colonization was severely reduced in roots of spr2 mutants. No association was found between levels of expression of genes coding for systemic wound responsive proteins (or SWRPs) and other defense-related proteins in roots and mycorrhization levels in these plants. On the other hand, the degree of mycorrhizal colonization correlated with changes in the transcriptional regulation of a number of genes involved in sucrose hydrolysis and transport, cell wall invertase activity and mycorrhizal-specific fatty acid content in roots. The results obtained suggest that one of the mechanisms by which JA might operate to modulate the mycorrhization process could be through its influence on the regulation of C partitioning in the plant. The significant colonization increase observed in mycorrhizal spr2 plants supplied with exogenous methyl jasmonate supports its role as a positive regulator of the symbiosis.

A cDNA, encoding a cysteine protease inhibitor (AhCPI), was isolated from an immature seed cDNA library of grain amaranth (Amaranthus hypochondriacus L.) and characterized. It encoded a polypeptide of 247 amino acids (aa), including a putative N-terminal signal peptide. Other relevant regions found in its sequence included the G and PW conserved aa motifs, the consensus LARFAV sequence for phytocystatins and the reactive site QVVAG. The predicted aa sequence for AhCPI showed a significant homology to other plant cystatins. Gene expression analyses indicated that AhCPI was constitutively expressed in mature seeds, and gradually decreased during germination. In vegetative tissues, AhCPI was expressed in the radicle and hypocotyls of seedlings and in the stems and roots of young plantlets. Its expression in roots and stems increased substantially in response to water deficit, salinity-, cold- and heat-stress, whereas heat-stress induced a rapid and transient accumulation of AhCPI transcripts in leaves. The results obtained were suggestive of multiple roles for AhCPI in grain amaranth, acting as a regulator of seed germination and as a protective agent against diverse types of abiotic stress, which induced this gene in a tissue- and stress-specific manner. The work herewith described reports a novel, and apparently, single cystatin protein in which, in agreement with other plant model systems, could have a regulatory role in germination, and further expands previous findings linking the accumulation of protease inhibitors, mostly of the serine proteinase type, with protection against (a)biotic stress in A. hypochondriacus.