Constitutive camalexin production and environmental stress response variation in Arabidopsis populations from the Iberian Peninsula

Abstract

Optimal defense theory predicts that induction of defensive secondary metabolites in plants will be inversely correlated with constitutive expression of those compounds. Here, we asked whether camalexin, an important defense against fungal and bacterial pathogens, support this prediction in structured natural populations of Arabidopsis thaliana from the Iberian Peninsula. In common garden experiments, we found that genotypes from the VIE population constitutively hyper-accumulated camalexin. Camalexin concentrations were not induced significantly when plants were exposed to a temperature of 10°C for 48h. However, they were induced when plants were exposed to 48h of infection by the virulent bacterial pathogen, Pseudomonas syringae pv. tomato DC3000. Genotypes from the VIE population with the hyper-accumulation of camalexin were significantly more resistant to bacterial growth. Induction of camalexin was negatively correlated with constitutive camalexin concentrations following log transformation and two different corrections for autocorrelation, thus supporting the tradeoff predicted by optimal defense theory. Constitutive overexpression of camalexin was not explained by the only known natural genetic polymorphism at the Accelerated Cell Death 6, ACD6, locus. Collectively, the results support an important role of camalexin in defense against P. syringae as well as significant structured variation in defense levels within wild populations.

Herbivory and Relative Growth Rates of Pieris rapae are Correlated with Host Constitutive Salicylic Acid and Flowering Time

“…The current study does not address intraspecific variation, which other studies have shown can be substantial with respect to leaf SA concentration (Silverman et al 1995 ; Zhang et al 2014 ) and the performance of Pieris larvae (Chew 1975 ). Broad conclusions about the host suitability and relative leaf SA contents of these ten mustards are, therefore, not warranted.…”

“…Much of what we know about these hormones has come from the study of a few major model systems (Vlot et al 2009 ). Little is known about how concentrations of these hormones vary in natural communities of plants and the extent to which this variation may structure plant – enemy interactions in nature (but see Todesco et al 2010 ; Zhang et al 2014 , 2015 ).…”

“…While exogenous treatment of plants with SA has been shown to increase the susceptibility to insect herbivores, the effects of constitutive variation in SA on plant resistance to insect herbivores has not been reported previously. Constitutive tissue concentrations of SA do differ among genotypes within species (Silverman et al 1995 ; Zhang et al 2014 ) and among species (Raskin 1992 ). Constitutive differences in allocation to SA among genotypes from natural populations of the widely-studied mustard, Arabidopsis thaliana , also have been shown recently to influence resistance to bacterial and fungal pathogens (Todesco et al 2010 ; Zhang et al 2014 ) and to vary geographically across an environmental gradient (Zhang et al 2015 ).…”

Adaptive divergence in transcriptome response to heat and acclimation inArabidopsis thalianaplants from contrasting climates

“…For example, sixteen 105 populations showed differential Hsp101 expression when exposed to a 42 o C compared 106 to a 45 o C heat treatment (Zhang et al 2015a), while salicylic acid differed among four 107 tested populations when exposed to a 44 o C heat treatment for 3hrs (Zhang et al 2015b). 108 These populations also show differential expression when exposed to cold stress and 109 pathogen infection (Zhang et al 2014 Larkindale and Vierling (2008) showed that two heat treatment 119 regimes, one with a moderately high temperature acclimation followed by high 120 temperature, the other a direct exposure to high temperature, have very different core 121 genome responses (Larkindale & Vierling 2008). Both the number and abundance of 122 transcripts up-regulated and down-regulated under heat stress (compared to the control 123 condition) differ between the two heat treatment regimes.…”

“…94 Our study region, the northeastern Iberian Peninsula, provides an ideal location for 95 studying the general patterns of response to climate in plants. Populations (Zhang et al 2014) .These native Arabidopsis populations also 104 show divergent response to various abiotic and biotic stresses. For example, sixteen 105 populations showed differential Hsp101 expression when exposed to a 42 o C compared 106 to a 45 o C heat treatment (Zhang et al 2015a), while salicylic acid differed among four 107 tested populations when exposed to a 44 o C heat treatment for 3hrs (Zhang et al 2015b).…”