Costs and Tradeoffs of Resistance and Tolerance to Belowground Herbivory in Potato

Sensitivity shift of the meta-metabolome and photosynthesis to the chemical stress in periphyton between months along one year and a half period: Case study of a terbuthylazine exposure

Despite the knowledge of the effects of contaminants on periphyton, information is limited about their natural fluctuations in sensitivity to chemical stress between various months. In particular, the molecular and biochemical mechanisms associated with sensitivity of photosynthesis and its fluctuations remain poorly described. To tackle this lack of knowledge, meta-metabolomics offers a comprehensive picture of the sensitive molecular response preceding the physiological impact. This study aimed to describe changes in the sensitivity of periphyton to chemical stress at different months over one year and a half period, at both the physiological and molecular levels by measuring photosynthetic yield and meta-metabolome responses (targeted and untargeted approaches). Periphyton was colonized for four weeks and then exposed to a range of terbuthylazine concentrations (0.3-30 μg L-1) under controlled conditions for 4 h. Sensitivity was assessed by determining the benchmark doses for the meta-metabolome and photosynthesis, along with the cumulative distribution of aggregated metabolomics signals. The results showed a strong sensitivity shift in the meta-metabolome compared to a smaller shift in photosynthetic yield at different months. This study also confirmed the high sensitivity of the meta-metabolome, as most signals responded before photosynthesis. The annotation highlighted the discrepancies in the molecular response to TBA between the months in terms of metabolite classes (e.g. amino acids, alkaloids, and lipids), their sensitivity, and trends in common classes across months, and correlation to photosynthesis inhibition, notably oxylipins. Overall, this study highlights that the molecular response of the periphyton to chemical stress, and thus toxicity pathways, may differ between the months but can still lead to similar physiological responses.

Plant genetic relatedness and volatile-mediated signalling between Solanum tuberosum plants in response to herbivory by Spodoptera exigua

It has been proposed that plant-plant signalling via herbivore-induced volatile organic compounds (VOCs) should be stronger between closely related than unrelated plants. However, empirical tests remain limited and few studies have provided detailed assessments of induced changes in VOCs emissions across plant genotypes to explain genetic relatedness effects. In this study, we tested whether airborne signalling in response to herbivory between Solanum tuberosum (potato) plants was contingent on plant genetic relatedness, and further investigated genotypic variation in VOCs potentially underlying signalling and its contingency on relatedness. We carried out a greenhouse experiment using 15 S. tuberosum varieties placing pairs of plants in plastic cages, i.e. an emitter and a receiver, where both plants were of the same genotype or different genotype thereby testing for self-recognition, an elemental form genetic relatedness effects. Then, for half of the cages within each level of relatedness the emitter plant was damaged by Spodoptera exigua larvae whereas for the other half the emitter was not damaged. Three days later, we placed S. exigua larvae on receivers to test for emitter VOC effects on leaf consumption and larval weight gain (i.e. induced resistance). In addition, we used a second group of plants subjected to the same induction treatment with the same S. tuberosum varieties to test for herbivore-induced changes in VOC emissions and variation in VOC emissions among these plant genotypes. We found that herbivory drove changes in VOC composition but not total emissions, and also observed quantitative and qualitative variation in constitutive and induced VOC emissions among varieties. Results from the bioassay showed that the amount of leaf area consumed and larval weight gain on receiver plants exposed to damaged emitters were significantly lower compared to mean values on receivers exposed to control emitters. However, and despite genotypic variation in induced VOCs, this signalling effect was not contingent on plant genetic relatedness. These findings provide evidence of VOCs-mediated signalling between S. tuberosum plants in response to S. exigua damage, but no evidence of self-recognition effects in signalling contingent on variation in VOC emissions among S. tuberosum varieties.

Characterization of STP4 promoter in Indian mustard Brassica juncea for use as an aphid responsive promoter

OBJECTIVE

Brassica juncea, a major oilseed crop, suffers substantial yield losses due to infestation by mustard aphids (Lipaphis erysimi). Unavailability of resistance genes within the accessible gene pool underpins significance of the transgenic strategy in developing aphid resistance. In this study, we aimed for the identification of an aphid-responsive promoter from B. juncea, based on the available genomic resources.

RESULTS

A monosaccharide transporter gene, STP4 in B. juncea was activated by aphids and sustained increased expression as the aphids colonized the plants. We cloned the upstream intergenic region of STP4 and validated its stand-alone aphid-responsive promoter activity. Further, deletion analysis identified the putative cis-elements important for the aphid responsive promoter activity.

CONCLUSION

The identified STP4 promoter can potentially be used for driving high level aphid-inducible expression of transgenes in plants. Use of aphid-responsive promoter instead of constitutive promoters can potentially reduce the metabolic burden of transgene-expression on the host plant.

Tecia solanivora infestation increases tuber starch accumulation in Pastusa Suprema potatoes

In response to infestation with larvae of the Guatemalan tuber moth (Tecia solanivora), some Solanum tuberosum (potato) varieties exhibit an overcompensation response, whereby the total dry mass of uninfested tubers is increased. Here, we describe early responses, within the first few days, of T. solanivora feeding, in the Colombian potato variety Pastusa Suprema. Non-targeted metabolite profiling showed significant secondary metabolism changes in T. solanivora-infested tubers, but not in uninfested systemic tubers. In contrast, changes in primary metabolism were greater in uninfested systemic tubers than in the infested tubers, with a notable 80% decline in systemic tuber sucrose levels within 1 d of T. solanivora infestation. This suggested either decreased sucrose transport from the leaves or increased sink strength, i.e., more rapid sucrose to starch conversion in the tubers. Increased sucrose synthesis was indicated by higher rubisco activase and lower starch synthase gene expression in the leaves of infested plants. Elevated sink strength was demonstrated by 45% more total starch deposition in systemic tubers of T. solanivora-infested plants compared to uninfested control plants. Thus, rather than investing in increased defense of uninfested tubers, Pastusa Suprema promotes deposition of photoassimilates in the form of starch as a response to T. solanivora infestation.