Amaranthus hypochondriacus, a grain amaranth, is a C4 plant noted by its ability to tolerate stressful conditions and produce highly nutritious seeds. These possess an optimal amino acid balance and constitute a rich source of health-promoting peptides. Although several recent studies, mostly involving subtractive hybridization strategies, have contributed to increase the relatively low number of grain amaranth expressed sequence tags (ESTs), transcriptomic information of this species remains limited, particularly regarding tissue-specific and biotic stress-related genes. Thus, a large scale transcriptome analysis was performed to generate stem- and (a)biotic stress-responsive gene expression profiles in grain amaranth.

Tomato plants release volatile organic compounds (VOCs) following insect or mechanical damage. In this study, the constitutive and wound‐induced emission levels of VOCs in suppressor of prosystemin‐mediated responses2 (spr2) mutant plants, compromised in linolenic acid (LA) and jasmonic acid (JA) synthesis, and in 35S::prosystemin (35S::prosys) plants, having upregulated direct defence responses, were compared. Thespr2mutants produced constitutively lower levels of VOCs, which were nonetheless increased in response to (a)biotic damage, although at lower levels than wild‐type (Wt) and35S::prosysplants. No significant differences in VOC emissions were detected between the latter two genotypes, thereby suggesting that systemin does not regulate indirect defence responses, whereas differences in fatty acid composition inspr2plants led to the predominant emission of saturated C6 volatiles in response to wounding. The expression of 1‐deoxy‐d‐xylulose 5‐phosphate synthase (DXS2), a key gene involved in VOC synthesis in the chloroplast, was only upregulated inManduca sextaL.‐damaged Wt and35S::prosysplants. However, its expression was restored inspr2plants by exogenous LA or JA, suggesting that abated VOC emissions inspr2plants are correlated with loweredDXS2expression. Bioassays with two different insects showed that adult females significantly preferredspr2plants, indicating that lowered levels of VOCs in tomato influence plant selection by insects during oviposition.

Background: Amaranthus cruentus and A. hypochondriacus are crop plants grown for grain production in subtropical countries. Recently, the generation of large-scale transcriptomic data opened the possibility to study representative genes of primary metabolism to gain a better understanding of the biochemical mechanisms underlying tolerance to defoliation in these species. A multi-level approach was followed involving gene expression analysis, enzyme activity and metabolite measurements. Results: Defoliation by insect herbivory (HD) or mechanical damage (MD) led to a rapid and transient reduction of non-structural carbohydrates (NSC) in all tissues examined. This correlated with a short-term induction of foliar sucrolytic activity, differential gene expression of a vacuolar invertase and its inhibitor, and induction of a sucrose transporter gene. Leaf starch in defoliated plants correlated negatively with amylolytic activity and expression of a β-amylase-1 gene and positively with a soluble starch synthase gene. Fatty-acid accumulation in roots coincided with a high expression of a phosphoenolpyruvate/phosphate transporter gene. In all tissues there was a long-term replenishment of most metabolite pools, which allowed damaged plants to maintain unaltered growth and grain yield. Promoter analysis of ADP-glucose pyrophosphorylase and vacuolar invertase genes indicated the presence of cis-regulatory elements that supported their responsiveness to defoliation. HD and MD had differential effects on transcripts, enzyme activities and metabolites. However, the correlation between transcript abundance and enzymatic activities was very limited. A better correlation was found between enzymes, metabolite levels and growth and reproductive parameters. Conclusions: It is concluded that a rapid reduction of NSC reserves in leaves, stems and roots followed by their long-term recovery underlies tolerance to defoliation in grain amaranth. This requires the coordinate action of genes/enzymes that are differentially affected by the way leaf damage is performed. Defoliation tolerance in grain is a complex process that can’t be fully explained at the transcriptomic level only.