Unbiased Transcriptional Comparisons of Generalist and Specialist Herbivores Feeding on Progressively Defenseless Nicotiana attenuata Plants

Background Herbivore feeding elicits dramatic increases in defenses, most of which require jasmonate (JA) signaling, and against which specialist herbivores are thought to be better adapted than generalist herbivores. Unbiased transcriptional analyses of how neonate larvae cope with these induced plant defenses are lacking. Methodology/Principal Findings We created cDNA microarrays for Manduca sexta and Heliothis virescens separately, by spotting normalized midgut-specific cDNA libraries created from larvae that fed for 24 hours on MeJA-elicited wild-type (WT) Nicotiana attenuata plants. These microarrays were hybridized with labeled probes from neonates that fed for 24 hours on WT and isogenic plants progressively silenced in JA-mediated defenses (N: nicotine; N/PI: N and trypsin protease inhibitors; JA: all JA-mediated defenses). H. virescens neonates regulated 16 times more genes than did M. sexta neonates when they fed on plants silenced in JA-mediated defenses, and for both species, the greater the number of defenses silenced in the host plant (JA > N/PI > N), the greater were the number of transcripts regulated in the larvae. M. sexta larvae tended to down-regulate while H. virescens larvae up- and down-regulated transcripts from the same functional categories of genes. M. sexta larvae regulated transcripts in a diet-specific manner, while H. virescens larvae regulated a similar suite of transcripts across all diet types. Conclusions/Significance The observations are consistent with the expectation that specialists are better adapted than generalist herbivores to the defense responses elicited in their host plants by their feeding. While M. sexta larvae appear to be better adapted to N. attenuata's defenses, some of the elicited responses remain effective defenses against both herbivore species. The regulated genes provide novel insights into larval adaptations to N. attenuata's induced defenses, and represent potential targets for plant-mediated RNAi to falsify hypotheses about the process of adaptation

Identification and functional validation of a unique set of drought induced genes preferentially expressed in response to gradual water stress in peanut

Peanut, found to be relatively drought tolerant crop, has been the choice of study to characterize the genes expressed under gradual water deficit stress. Nearly 700 genes were identified to be enriched in subtractive cDNA library from gradual process of drought stress adaptation. Further, expression of the drought inducible genes related to various signaling components and gene sets involved in protecting cellular function has been described based on dot blot experiments. Fifty genes (25 regulators and 25 functional related genes) selected based on dot blot experiments were tested for their stress responsiveness using northern blot analysis and confirmed their nature of differential regulation under different field capacity of drought stress treatments. ESTs generated from this subtracted cDNA library offered a rich source of stress-related genes including signaling components. Additional 50% uncharacterized sequences are noteworthy. Insights gained from this study would provide the foundation for further studies to understand the question of how peanut plants are able to adapt to naturally occurring harsh drought conditions. At present functional validation cannot be deemed in peanut, hence as a proof of concept seven orthologues of drought induced genes of peanut have been silenced in heterologous N. benthamiana system, using virus induced gene silencing method. These results point out the functional importance for HSP70 gene and key regulators such as Jumonji in drought stress response

Activation of drought tolerant traits in crops: endophytes as elicitors

Drought challenges crop production worldwide. The issue is aggravated by frequent drought episodes and unpredictable rainfall patterns associated with global climate change. While the efforts to breed drought-resistant crop varieties are progressing, the need of the hour is immediate strategies to sustain the yields of existing ones. As per recent studies, stress adaptive traits can be activated using specific elicitors. Endophytes that inhabit host plants asymptomatically are natural elicitors/bio-stimulators capable of activating host gene expression, conferring several benefits to the hosts. This review discusses the scope of using trait-specific endophytes in activating drought adaptive traits in crop varieties

Genetic diversity for grain Zn concentration in finger millet genotypes: Potential for improving human Zn nutrition

Nearly half of the world population suffers from micronutrient malnutrition, particularly Zn deficiency. It is important to understand genetic variation for uptake and translocation behaviors of Zn in relevant crop species to increase Zn concentration in edible parts. In the present study, genetic variation in grain Zn concentration of 319 finger millet genotypes was assessed. Large genetic variation was found among the genotypes, with concentrations ranging from 10 to 86 μg g− 1 grain. Uptake and translocation studies with Zn/65Zn application in 12 selected low-Zn genotypes showed wide variation in root uptake and shoot translocation, with genotypes GEC331 and GEC164 showing greater uptake and translocation. Genotypes GEC164 and GEC543 showed increased grain Zn concentration. Genotypes GEC331 and GEC164 also showed improved yield under Zn treatment. Appreciable variation in grain Zn concentration among finger millet genotypes found in this study offers opportunities to improve Zn nutrition through breeding

MAPK-dependent JA and SA signalling in <it>Nicotiana attenuata</it> affects plant growth and fitness during competition with conspecifics

Abstract Background Induced defense responses to herbivores are generally believed to have evolved as cost-saving strategies that defer the fitness costs of defense metabolism until these defenses are needed. The fitness costs of jasmonate (JA)-mediated defenses have been well documented. Those of the early signaling units mediating induced resistance to herbivores have yet to be examined. Early signaling components that mediate herbivore-induced defense responses in Nicotiana attenuata, have been well characterized and here we examine their growth and fitness costs during competition with conspecifics. Two mitogen-activated protein kinases (MAPKs), salicylic acid (SA)-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK) are rapidly activated after perception of herbivory and both kinases regulate herbivory-induced JA levels and JA-mediated defense metabolite accumulations. Since JA-induced defenses result in resource-based trade-offs that compromise plant productivity, we evaluated if silencing SIPK (irSIPK) and WIPK (irWIPK) benefits the growth and fitness of plants competiting with wild type (WT) plants, as has been shown for plants silenced in JA-signaling by the reduction of Lipoxygenase 3 (LOX3) levels. Results As expected, irWIPK and LOX3-silenced plants out-performed their competing WT plants. Surprisingly, irSIPK plants, which have the largest reductions in JA signaling, did not. Phytohormone profiling of leaves revealed that irSIPK plants accumulated higher levels of SA compared to WT. To test the hypothesis that these high levels of SA, and their presumed associated fitness costs of pathogen associated defenses in irSIPK plants had nullified the JA-deficiency-mediated growth benefits in these plants, we genetically reduced SA levels in irSIPK plants. Reducing SA levels partially recovered the biomass and fitness deficits of irSIPK plants. We also evaluated whether the increased fitness of plants with reduced SA or JA levels resulted from increased nitrogen or CO2 assimilation rates, and found no evidence that greater intake of these fitness-limiting resources were responsible. Conclusions Signaling mediated by WIPK, but not SIPK, is associated with large fitness costs in competing N. attenuata plants, demonstrating the contrasting roles that these two MAPKs play in regulating the plants’ growth-defense balance. We discuss the role of SIPK as an important regulator of plant fitness, possibly by modulating SA-JA crosstalk as mediated through ethylene signaling.</p

Aberrant imprinting may underlie evolution of parthenogenesis

Genomic imprinting confers parent-of-origin-specific gene expression, thus non-equivalent and complementary function of parental genomes. As a consequence, genomic imprinting poses an epigenetic barrier to parthenogenesis in sexual organisms. We report aberrant imprinting in Boechera, a genus in which apomicts evolved from sexuals multiple times. Maternal activation of a MADS-box gene, a homolog of which is imprinted and paternally expressed in the sexual relative Arabidopsis, is accompanied by locus-specific DNA methylation changes in apomicts where parental imprinting seems to be relaxed

Aberrant imprinting may underlie evolution of parthenogenesis

Genomic imprinting confers parent-of-origin-specific gene expression, thus non-equivalent and complementary function of parental genomes. As a consequence, genomic imprinting poses an epigenetic barrier to parthenogenesis in sexual organisms. We report aberrant imprinting in Boechera, a genus in which apomicts evolved from sexuals multiple times. Maternal activation of a MADS-box gene, a homolog of which is imprinted and paternally expressed in the sexual relative Arabidopsis, is accompanied by locus-specific DNA methylation changes in apomicts where parental imprinting seems to be relaxed.</p