Spectral Reflectance Indexes Reveal Differences in the Physiological Status of Brassica oleracea with Contrasting Glucosinolate Content under Biotic Stress.

Brassica species produce glucosinolates, a specific group of secondary metabolites present in the Brassicaceae family with antibacterial and antifungal properties. The employment of improved varieties for specific glucosinolates would reduce the production losses caused by pathogen attack. However, the consequences of the increment in these secondary metabolites in the plant are unknown. In this work, we utilized reflectance indexes to test how the physiological status of Brasica oleracea plants changes depending on their constitutive content of glucosinolates under nonstressful conditions and under the attack of the bacteria Xanthomonas campestris pv. campestris and the fungus Sclerotinia sclerotiorum. The modification in the content of glucosinolates had consequences in the resistance to both necrotrophic pathogens, and in several physiological aspects of the plants. By increasing the content in sinigrin and glucobrassicin, plants decrease photosynthesis efficiency (PR531, FvFm), biomass production (CHL-NDVI, SR), pigment content (SIPI, NPQI, RE), and senescence (YI) and increase their water content (WI900). These variables may have a negative impact in the productivity of crops in an agricultural environment. However, when plants are subjected to the attack of both necrotrophic pathogens, an increment of sinigrin and glucobrassicin confers an adaptative advantage to the plants, which compensates for the decay of physiological parameters.

Epigenetic and Phenotypic Responses to Experimental Climate Change of Native and Invasive Carpobrotus edulis.

Despite the recent discoveries on how DNA methylation could help plants to adapt to changing environments, the relationship between epigenetics and climate change or invasion in new areas is still poorly known. Here, we investigated, through a field experiment, how the new expected climate scenarios for Southern Europe, i.e., increased temperature and decreased rainfall, might affect global DNA methylation in relation to phenotypic variation in individuals of clonal plant, Carpobrotus edulis, from its native (Southern African) and invaded (northwestern Iberian Peninsula) area. Our results showed that changes in temperature and rainfall induced phenotypic but not global DNA methylation differences among plants, and the climatic effects were similar for plants coming from the native or invaded areas. The individuals from the Iberian Peninsula showed higher levels of global methylation than their native counterparts from South Africa. We also observed differences between natives and invasive phenotypes in traits related to the pattern of biomass partitioning and to the strategies for water uptake and use and found an epigenetic contribution to phenotypic changes in some leaf traits, especially on the nitrogen isotopic composition. We conclude that the increased temperature and decreased rainfall projected for Southern Europe during the course of the twenty-first century may foster phenotypic changes in C. edulis, possibly endowing this species with a higher ability to successful cope the rapid environmental shifts. The epigenetic and phenotypic divergence that we observed between native and invasive plants suggests an intraspecific functional variation during the process of invasion. This result could indicate that phenotypic plasticity and global DNA methylation are related to the colonization of new habitats. Our findings reinforce the importance of epigenetic plasticity on rapid adaptation of invasive clonal plants.

Functional responses to climate change may increase invasive potential of Carpobrotus edulis.

PREMISE: Biological invasions and climate change are major threats to biodiversity. It is therefore important to anticipate how the climate changes projected for Southern Europe would affect the ecophysiological performance of the invasive South African plant, Carpobrotus edulis (ice plant or sour fig), and its capacity to undergo rapid adaptive evolution. METHODS: We manipulated the climate conditions in a field plot located on the island of Sálvora (northwest of the Iberian Peninsula) to establish a full factorial experiment with C. edulis plants transplanted from four native (southern African) and four invasive (northwestern Iberian Peninsula) populations. Throughout 14 months we measured growth and functional traits of this species under two temperatures (control vs. increased), and two rainfall levels (control vs. reduced). RESULTS: Temperature increased photochemical efficiency and relative growth rate of C. edulis. Rainfall modulated some of the effects of temperature on C and N isotopic composition, and pigment contents. Invasive populations showed lower root mass allocation and higher survival rates, as well as increased water use efficiency, lipid peroxidation, chlorophyll, and xanthophyll cycle pigment contents than native populations. CONCLUSIONS: The increased growth and physiological performances observed under our experimental conditions suggest that the expected climate changes would further promote the invasion of C. edulis. Differences between native and invasive genotypes in survival and functional traits revealed that populations have diverged during the process of invasion, what gives support to the invasiveness hypothesis. Our findings highlight the importance of analyzing intraspecific variability in functional responses to better predict how invasive species will respond to environmental changes.

Transcriptomic Reprograming of Xanthomonas campestris pv. campestris after Treatment with Hydrolytic Products Derived from Glucosinolates.

The bacterium Xanthomonas campestris pv. campestris (Xcc) causes black rot disease in Brassica crops. Glucosinolates are known to be part of the defence system of Brassica crops against Xcc infection. They are activated upon pathogen attack by myrosinase enzymes. Their hydrolytic products (GHPs) inhibit the growth of Xcc in vitro. However, the mechanisms underlying this inhibition and the way Xcc can overcome it are not well understood. We studied the transcriptomic reprogramming of Xcc after being supplemented with two chemically different GHPs, one aliphatic isothiocyanate (allyl-ITC) and one indole (indol-3-carbinol), by RNA-seq. Based on our results, the arrest in Xcc growth is related to the need to stop cell division to repair damaged DNA and cell envelope components. Otherwise, GHPs modify energy metabolism by inhibiting aerobic respiration and increasing the synthesis of glycogen. Xcc induces detoxification mechanisms such as the antioxidant defence system and the multidrug efflux system to cope with the toxic effects driven by GHPs. This is the first time that the transcriptomic reprogramming of a plant pathogenic bacterium treated with GHPs has been studied. This information will allow a better understanding of the interaction of a plant pathogen mediated by GSLs.

Sclerotinia sclerotiorum Response to Long Exposure to Glucosinolate Hydrolysis Products by Transcriptomic Approach.

White mold disease, caused by the necrotrophic fungus Sclerotinia sclerotiorum, affects Brassica crops. Brassica crops produce a broad array of compounds, such as glucosinolates, which contribute to the defense against pathogens. From their hydrolysis, several products arise that have antimicrobial activity (GHPs) whose toxicity is structure dependent. S. sclerotiorum may overcome the toxic effect of moderate GHP concentrations after prolonged exposure to their action. Our objective was to identify the molecular mechanism underlying S. sclerotiorum response to long exposure to two chemically diverse GHPs: aliphatic GHP allyl-isothiocyanate (AITC) and indole GHP indol-3-carbinol (I3C). We found that the transcriptomic response is dependent on the type of GHP and on their initial target, involving cell membranes in the case of AITC or DNA in the case of I3C. Response mechanisms include the reorganization of chromatin, mediated by histone chaperones hip4 and cia1, ribosome synthesis controlled by the kinase-phosphatase pair aps1-ppn1, catabolism of proteins, ergosterol synthesis, and induction of detoxification systems. These mechanisms probably help S. sclerotiorum to grow and survive in an environment where GHPs are constantly produced by Brassica plants upon glucosinolate breakdown. IMPORTANCEBrassica species, including important vegetable crops, such as cabbage, cauliflower, or broccoli, or oil crops, such as rapeseed, produce specific chemical compounds useful to protect them against pests and pathogens. One of the most destructive Brassica diseases in temperate areas around the world is Sclerotinia stem rot, caused by the fungus Sclerotinia sclerotiorum. This is a generalist pathogen that causes disease over more than 400 plant species, being a serious threat to economically important crops worldwide, including potato, bean, soybean, and sunflower, among many others. Understanding the mechanisms utilized by pathogens to overcome specific plant defensive compounds can be useful to increase plant resistance. Our study demonstrated that Sclerotinia shows different adaptation mechanisms, including detoxification systems, to grow and survive when plant protective compounds are present.

Role of Major Glucosinolates in the Defense of Kale Against Sclerotinia sclerotiorum and Xanthomonas campestris pv. campestris.

Glucosinolates (GSLs) are secondary metabolites present in Brassicaceae species implicated in their defense against plant pathogens. When a pathogen causes tissue damage, the enzyme myrosinase hydrolyzes GSLs into diverse products that exhibit antimicrobial activity against a wide range of bacteria and fungi in vitro. It was demonstrated that modulation of GSL content in vivo affects plant resistance to infection by pathogens in Arabidopsis. However, the roles of specific metabolites and how they interact with pathogens are poorly understood in Brassica crops. We previously developed a set of populations of Brassica oleracea var. acephala L. (kale) differing in content of three GSLs: the aliphatics sinigrin (2-propenyl [SIN]) and glucoiberin (3-methylsulphinylpropyl [GIB]) and the indolic glucobrassicin (3-indolylmethyl [GBS]). These populations can be used to study the effects of major GSLs in kale, with the advantage that genotypes within each selection have the same genetic background. This research aimed to explore the role of SIN, GIB, and GBS in the defense of kale against the necrotrophic fungus Sclerotinia sclerotiorum and the bacterium Xanthomonas campestris pv. campestris. Results showed that increasing the amount of a particular GSL did not always result in disease resistance. The effects of GSLs were apparently dependent on the pathogen and the type of GSL. Thus, the aliphatic SIN was inhibitory to infection by S. sclerotiorum and the indolic GBS was inhibitory to infection by X. campestris pv. campestris. Other factors, including the quantity and proportion of other metabolites modified during the pathogen infection process, could also modulate the degree of inhibition to the pathogen.

In vivo and in vitro effects of secondary metabolites against Xanthomonas campestris pv. campestris.

Brassica rapa is a crucifer that is grown worldwide, mainly as a vegetable. The quality of B. rapa crops is highly affected by the disease caused by the bacteria Xanthomonas campestris pv. campestris (Xcc). Glucosinolates and phenolic compounds can confer resistance to Brassica crops against pests and diseases, but few works have been done to evaluate their role in Xcc resistance. The objectives of this work were: (1) to evaluate the in vivo and in vitro antibacterial effect of gluconapin, its isothiocyanate and the methanolic extracts of B. rapa against the type 4 of Xcc, and (2) to test if there is induced resistance mediated by glucosinolates or phenolic compounds in two varieties of B. rapa. Gluconapin and its ITC varieties had an antibacterial effect on the development of Xanthomonas and this effect was strongly dependent on the concentration applied. Methanolic extracts from B. rapa, containing glucosinolates and phenolic compounds, inhibited the growth of these bacteria. Concentration of gluconapin is higher in resistant plants than in the susceptible ones and there is an induction of gluconapin, some flavonoids and sinapic acid 48 to 72 h after inoculation. Gluconapin plays a role in the constitutive resistance to Xcc, while gluconapin, some flavonoids and hydroxycinnamic acids are induced by a Xcc infection but it is not clear if this induction confers resistance to this disease.

Inheritance of White Mold Resistance in Phaseolus vulgaris × P. coccineus Crosses.

The fungus Sclerotinia sclerotiorum, cause of white mold, is known to attack >400 plant species. It is a widespread problem in dry bean (Phaseolus vulgaris) in the United States, causing >30% average yield losses. Low to moderate levels of resistance are found in dry bean. However, some accessions of P. coccineus (commonly known as scarlet runner bean) possess a relatively higher level of resistance. Our objective was to verify the reaction of 13 known white mold-resistant P. coccineus germ plasms and determine inheritance of resistance in accessions PI 433246 and PI 439534. Pinto Othello was crossed with PI 433246, and the resulting interspecific F1 was back-crossed onto Othello and allowed to produce F2 seed. Similarly, pinto UI 320 was crossed with PI 439534. The F1 was backcrossed onto UI 320 and allowed to produce F2 seed. The two parents, F1, F2, and backcross to dry bean of each set were evaluated in the greenhouse using the straw test at Fort Collins, CO in 2004. All 13 P. coccineus accessions and the two F2 also were evaluated using the modified petiole test at Kimberly, ID in 2005. All 13 P. coccineus accessions were variable in a 2002 straw test when rated for white mold reaction on a 1-to-9 scale, because the mean disease score ranged from 1.9 for PI 433246 to 4.4 for PI 189023 and 8.8 for the susceptible check Bill Z. For the petiole test, when rated on a 1-to-9 scale, the accessions exhibited an intermediate white mold score of 4 or 5 in 2005. In 2004, the susceptible check Othello exhibited a mean score of 7.9 compared with 3.4, 3.2, and 2.1 for PI 433246, UI 320, and PI 439534, respectively. The white mold reaction of PI 433246 and PI 439534 was dominant in their respective F1. The F2 segregation further indicated that white mold resistance in PI 433246 and PI 439534 was controlled by a single dominant gene. These two and other white mold-resistant P. coccineus accessions and selected breeding lines from the interspecific crosses should be useful for future improvement of white mold resistance of pinto and other market classes of dry and green or snap bean.