Sastry S. Jayanty

Regulation and Function of Arabidopsis JASMONATE ZIM-Domain Genes in Response to Wounding and Herbivory

Jasmonate (JA) and its amino acid conjugate, jasmonoyl-isoleucine (JA-Ile), play important roles in regulating plant defense responses to insect herbivores. Recent studies indicate that JA-Ile promotes the degradation of JASMONATE ZIM-domain (JAZ) transcriptional repressors through the activity of the E3 ubiquitin-ligase SCFCOI1. Here, we investigated the regulation and function of JAZ genes during the interaction of Arabidopsis (Arabidopsis thaliana) with the generalist herbivore Spodoptera exigua. Most members of the JAZ gene family were highly expressed in response to S. exigua feeding and mechanical wounding. JAZ transcript levels increased within 5 min of mechanical tissue damage, coincident with a large (approximately 25-fold) rise in JA and JA-Ile levels. Wound-induced expression of JAZ and other CORONATINE-INSENSITIVE1 (COI1)-dependent genes was not impaired in the jar1-1 mutant that is partially deficient in the conversion of JA to JA-Ile. Experiments performed with the protein synthesis inhibitor cycloheximide provided evidence that JAZs, MYC2, and genes encoding several JA biosynthetic enzymes are primary response genes whose expression is derepressed upon COI1-dependent turnover of a labile repressor protein(s). We also show that overexpression of a modified form of JAZ1 (JAZ1Δ3A) that is stable in the presence of JA compromises host resistance to feeding by S. exigua larvae. These findings establish a role for JAZ proteins in the regulation of plant anti-insect defense, and support the hypothesis that JA-Ile and perhaps other JA derivatives activate COI1-dependent wound responses in Arabidopsis. Our results also indicate that the timing of JA-induced transcription in response to wounding is more rapid than previously realized.

Role of β-Oxidation in Jasmonate Biosynthesis and Systemic Wound Signaling in Tomato

Jasmonic acid (JA) is a lipid-derived signal that regulates plant defense responses to biotic stress. Here, we report the characterization of a JA-deficient mutant of tomato (Lycopersicon esculentum) that lacks local and systemic expression of defensive proteinase inhibitors (PIs) in response to wounding. Map-based cloning studies demonstrated that this phenotype results from loss of function of an acyl-CoA oxidase (ACX1A) that catalyzes the first step in the peroxisomal β-oxidation stage of JA biosynthesis. Recombinant ACX1A exhibited a preference for C12 and C14 straight-chain acyl-CoAs and also was active in the metabolism of C18 cyclopentanoid-CoA precursors of JA. The overall growth, development, and reproduction of acx1 plants were similar to wild-type plants. However, the mutant was compromised in its defense against tobacco hornworm (Manduca sexta) attack. Grafting experiments showed that loss of ACX1A function disrupts the production of the transmissible signal for wound-induced PI expression but does not affect the recognition of this signal in undamaged responding leaves. We conclude that ACX1A is essential for the β-oxidation stage of JA biosynthesis and that JA or its derivatives is required both for antiherbivore resistance and the production of the systemic wound signal. These findings support a role for peroxisomes in the production of lipid-based signaling molecules that promote systemic defense responses.

Tomato MAPKs LeMPK1, LeMPK2, and LeMPK3 function in the systemin-mediated defense response against herbivorous insects

Systemin is a wound-signaling peptide that mediates defenses of tomato plants against herbivorous insects. Perception of systemin by the membrane-bound receptor SR160 results in activation of MAPKs, synthesis of jasmonic acid (JA), and expression of defense genes. To test the function of MAPKs in the response to systemin, we used virus-induced gene silencing (VIGS) in plants that overexpress the systemin precursor prosystemin (35S::prosys plants). These transgenic plants accumulate high levels of defense proteins and exhibit increased resistance to herbivorous insects. Cosilencing of the MAPKs MPK1 and MPK2 reduced MPK1/2 kinase activity, JA biosynthesis, and expression of JA-dependent defense genes. Application of methyl-JA restored the full defense response. These data show that MPK1 and MPK2 are essential components of the systemin signaling pathway and most likely function upstream of JA biosynthesis. MPK1 and MPK2 are 95% identical at the amino acid level. Specific VIGS of only MPK1 or MPK2 resulted in the same reduction of defense gene expression as cosilencing of MPK1 and MPK2, indicating that gene dosage effects may be important for MPK signaling. In addition, VIGS of the closely related MPK3 also reduced systemin-induced defense responses. The function of MPK1/2 and orthologs in pathogen-induced defenses is well established. Here we show that cosilencing of MPK1 and MPK2 compromised prosystemin-mediated resistance to Manduca sexta (Lepidoptera) herbivory, demonstrating that MPK1 and MPK2 are also required for successful defenses against herbivorous insects.

Pyrosequencing Assessment of Soil Microbial Communities in Organic and Conventional Potato Farms

Organic farming is frequently touted as being beneficial to soil health by increasing microbial community diversity; however, contradictory results exist in the literature. In this study, we compared several organic and conventional potato farms in Colorado for differences in soil nutrients and microbial communities using 454 pyrosequencing of the 18S ribosomal RNA gene. Organic farms showed a slightly higher diversity and evenness within the microbial community compared with conventional farms. No difference in the number of observed or estimated total operational taxonomic units (OTUs) was observed between management strategies. However, the relative abundance of 16 OTUs (3% genetic distance) differed between the organic and conventional farms, with seven increasing and nine decreasing in organic farms. A variety of known potato fungal pathogens (e.g., Alternaria spp., Ulocladium spp., and Pythium ultimum) were detected in the soil, including three different OTUs (3% genetic distance) with a high homology to the early blight pathogen Alternaria solani. Relative abundance for Alternaria spp. was higher in conventional farms (relative abundance 30.15 versus 7.8%), whereas the relative abundance for P. ultimum was higher in organic farms (relative abundance 0.25 versus 0.05%). Quantitative polymerase chain reaction, using primers specific for A. solani, Phoma foveata, and Pythium ultimum, yielded similar results to the pyrosequencing, validating the use of pyrosequencing data for the quantification of OTU relative abundances.

Reduction of acrylamide formation by vanadium salt in potato French fries and chips.

The effects of vanadyl sulphate on the formation of acrylamide have been studied in fried potato products, such as French fries and chips. Acrylamide formation was inhibited by 30.3%, 53.3% and 89.3% when the sliced potato strips were soaked in 0.001, 0.01 and 0.1 M vanadyl sulphate (VOSO(4)) solutions, respectively, for 60 min before frying. Moreover, 57.7%, 71.4% and 92.5% inhibition of acrylamide formation was observed when chips were soaked in the respective vanadyl sulphate solution before frying. In a separate model reaction, a solution containing an equimolar concentration of L-asparagine and D-glucose showed a significant inhibition of acrylamide formation when heated at 150 °C for 30 min in the presence of vanadyl sulphate (VOSO(4)). The results indicate that the binding of VO(2+) to asparagine and the decrease in the pH of the potato samples resulted in a significant reduction of acrylamide formation in fried potato products.

Biguanide related compounds in traditional antidiabetic functional foods.

Biguanides such as metformin are widely used worldwide for the treatment of type-2 diabetes. The identification of guanidine and related compounds in French lilac plant (Galega officinalis L.) led to the development of biguanides. Despite of their plant origin, biguanides have not been reported in plants. The objective of this study was to quantify biguanide related compounds (BRCs) in experimentally or clinically substantiated antidiabetic functional plant foods and potatoes. The corrected results of the Voges-Proskauer (V-P) assay suggest that the highest amounts of BRCs are present in green curry leaves (Murraya koenigii (L.) Sprengel) followed by fenugreek seeds (Trigonella foenum-graecum L.), green bitter gourd (Momordica charantia Descourt.), and potato (Solanum tuberosum L.). Whereas, garlic (Allium sativum L.), and sweet potato (Ipomea batatas (L.) Lam.) contain negligible amounts of BRCs. In addition, the possible biosynthetic routes of biguanide in these plant foods are discussed.

Selenium and Sulfur Content and Activity of Associated Enzymes in Selected Potato Germplasm

Potato plants are being supplemented with selenium (Se) to enrich tubers with Se for health benefits. Se is not an essential nutrient and interferes with the metabolism of sulfur (S) in plants. The objective of the present investigation was to study the activities of Se-independent glutathione peroxidase (Se-Ind-GPx), Se-dependent glutathione peroxidase (Se-Dep-GPx), and thioredoxin reductase (TRxR) enzymes in stored potato tubers grown on a non-Se-enriched field; and assess their relationship with tuber Se and S levels. The results indicate that these enzyme activities and the Se and S levels in the tubers were significantly influenced by genotype. Se-Dep-GPx activities were influenced by Se levels in the tubers. S content of tubers of all genotypes tested were below the critical nutrition concentration. In spite of this deficiency, the levels of S (which were very high in comparison with Se) influenced the activities of Se-Ind-GPx and TRxR in the tubers. Tubers of some of the genotypes tested can supply more than the recommended dietary allowance (RDA) of Se to adult humans.ResumenLas plantas de papa están siendo suplementadas con selenio (Se) para enriquecer los tubérculos con Se para beneficio de la salud. El Se no es un nutrimento esencial e interfiere con el metabolismo del azufre (S) en plantas. El objetivo de la presente investigación fue estudiar las actividades de las enzimas glutatión-peroxidasa independiente de Se (Se-Ind-GPx), glutatión-peroxidasa dependiente de Se (Se-Dep-GPx) y thioredoxin reductasa (TRxR) en tubérculos de papa almacenados provenientes de un campo no enriquecido con Se; y analizar su relación con los niveles de Se y S en el tubérculo. Los resultados indican que las actividades de estas enzimas y los niveles de Se y S en tubérculos fueron influenciados significativamente por el genotipo. Las actividades de Se-Dep-GPx se influenciaron por los niveles de Se en los tubérculos. El contenido de S en tubérculos de todos los genotipos probados estuvo debajo de la concentración crítica de nutrición. A pesar de esta deficiencia, los niveles de S (que fueron muy altos en comparación de Se) influenciaron las actividades de Se-Ind-GPx y TRxR en los tubérculos. Tubérculos de algunos de los genotipos probados pueden surtir mas de lo recomendado para la dieta de Se en humanos adultos.

Comparison of polyphenol content and antioxidant capacity of colored potato tubers, pomegranate and blueberries.

Dietary antioxidants from fruits and vegetables play an important role in preventing free radical-induced oxidative damage to lipids, proteins, and nucleic acids. Potato tubers with purple- and red-colored flesh contain high levels of phenolics and anthocyanins, as do pomegranates and blueberries. The present study evaluates the antioxidant potential of colored-flesh potato tubers in comparison with polyphenol-rich fruits, blueberries and pomegranate juice. The ranges of total phenolics (TP), total anthocyanins (TA), and total flavonoids (TF) were (4482 – 11189 μg/g), (1889 – 6289 μg/g), and (140-503 μg/g), respectively. The potential antioxidant capacities of the potato tubers were similar to that of pomegranate and blueberry. High correlations of TP, TA, and TF with antioxidant activity, such as ORAC, ABTS, and DPPH (r=0.95, 0.93, and 0.80 for TP; r=0.93, 0.96, and 0.54 for TA; r=0.80, 0.91, and 0.70 for TF), were found for the materials tested. The total antioxidant activity values per serving size of baked red and purple potatoes, blueberries, and pomegranate juice were also found to have comparable ranges.

Inhibition of α-glucosidase, α-amylase, and aldose reductase by potato polyphenolic compounds

Diabetes mellitus is a chronic disease that is becoming a serious global health problem. Diabetes has been considered to be one of the major risks of cataract and retinopathy. Synthetic and natural product inhibitors of carbohydrate degrading enzymes are able to reduce type 2 diabetes and its complications. For a long time, potatoes have been portrayed as unhealthy for diabetic patients by some nutritionist due to their high starch content. However, purple and red potato cultivars have received considerable attention from consumers because they have high levels of polyphenolic compounds that have potent antioxidant activities. In this study, we screened the total phenolics (TP) and total anthocyanins (TA) and analyzed the phenolic and anthocyanin compounds in selected potato cultivars and advanced selections with distinct flesh colors (purple, red, yellow and white). Purple and red potato cultivars had higher levels of TP and TA than tubers with other flesh colors. Chlorogenic acid is the predominant phenolic acid, and major anthocyanin is composed of the derivatives of petunidin, peonidin, malvidin and pelargonidin. We tested the potential inhibitory effect of potato extracts on the activities of α-amylase and α-glucosidase, which were targeted to develop antidiabetic therapeutic agents. We also measured inhibitory effect of potato extracts on aldose reductase (AR) which is a key enzyme that has been a major drug target for the development of therapies to treat diabetic complications. Purple flesh tubers extract showed the most effective inhibition of α-amylase, α-glucosidase, and aldose reductase with IC50 values 25, 42, and 32 μg/ml, respectively. Kinetic studies showed that anthocyanins are noncompetitive inhibitors of these enzymes, whereas phenolic acids behaved as mixed inhibitors for α-amylase and α-glucosidase and noncompetitive inhibitors for AR. This study supports the development of a positive and healthful image of potatoes, which is an important issue for consumers.

Nutrient Composition of Continuous and Kettle Cooked Potato Chips from Three Potato Cultivars

Potatoes are a good source of various nutritional and health promoting compounds such as Vitamin C, dietary fibers, potassium, magnesium, and carbohydrates. One of its fried products “potato chips” is the most popular snacks among consumers of all ages. This study presents useful data on total fats, reducing sugars, Vitamin C, minerals, total phenolics, antioxidant activity, glycoalkaloids, and acrylamide levels of potato chips made from three potato cultivars (Snowden, Lamoka, and Atlantic) grown at different locations in the USA. From the results obtained, these potato chips are notable for their high content of vitamin C (min, 6.54 max, 29.79 mg/100g), K (min, 1.10 max, 1.65 %), and dietary fibers (2.14 to 3.71 %). The average levels of acrylamide were 902.02 μg/kg with a range 866.96 948.7 in continuous frying chips and 873.369 μg/kg in kettle cooked chips with the range 840.06 932.76. Kettle cooked potato chips retained a higher amount of nutrients and lower level of fats. article History Received: 28 March 2017 Accepted:19 July 2017