acid (18:1) caused by mutation of a gene encoding STEAROYL- ACYL CARRIER PROTEIN-DESATURASE, increases the expression level of PR genes in a SA-dependent way, but at the same time, reduces expression of a subset of JA-dependent response genes and decreases resistance to Botryris cinerea in Arabidopsis [7]. A kind of PUFAs that impact plant defense responses are the eicosapolyenoic acids, which are produced and released by several species of oomycete plant pathogens. Specifically, exogenous application of arachidonic acid (20:4) to Arabidopsis and tomato (Solanum lycopersicum) plants induces expression of general-stress responsive genes, increases endoge- nous JA levels and confers resistance against the necrotrophic fungi Botrytis cinerea [8]. Based on this evidence, it has been proposed that lipids and their derivates have transorganismal signaling activity, and that their dependent pathways are conserved throughout the evolutive history of organisms [8]. Commonly, the full range of biological effects triggered by PUFA signals, are carried out by their metabolism into more potent substances, the oxylipins. Oxylipins are a diverse class of lipid metabolites that include fatty acid hydroxiperoxides, hydroxy-, oxo- , or keto-fatty acids, volatile aldehydes, or mostly, jasmonates (JAs) [9]. JAs act as regulatory molecules in metabolic and developmental processes, as well as in defense responses [10,11,12]. They rapidly accumulate by wounding, insect attack and necrotrophic pathogen infection [13]. JA is synthesized through a series of reactions involving lipoxygenases (LOXs), allene oxide synthases (AOSs), allene oxide cyclases (AOCs) and 12-oxophytodienoate reductases (OPRs). Then, JA is further modified to produce JAs, for example, as conjugates with various lipophilic amino acids such as isoleucine (Ile) produced by a jasmonate amino acid synthetase, encoded by JASMONATE RESISTANT1 (JAR1). The JA signal (JA-Ile) is perceived by an intracellular receptor, the F-box protein COI1, which plays a key role in JA signaling [14], and is required for the majority of the JA-mediated responses described to date, such as fertility, secondary metabolite biosynthesis, pest and pathogen resistance, and wound responses [15]. COI1 is an E3 ubiquitin ligase that catalyzes the ubiquitination of proteins destined to degradation via the proteosome-mediated pathway. COI1 activates a signal transduction pathway that culminates in the transcriptional activation or repression of JA-responsive genes. The coi1 mutant is resistant to JAs and to the Pseudomonas syringae toxin coronatine. The essential role of JAs in plant immunity is also evidenced by JA- related mutant phenotypes, for example both jar1 and coi1 show an enhanced susceptibility to necrotrophic pathogens [16,17]. In addition, protein phosphorylation and dephosphorylation have important roles in JA signaling. The mitogen-activated protein kinase (MAPK) cascade, which is one of the major signal transduction pathways in plants, as well as other eukaryotes, has been found to be regulated by JA to modulate JA-dependent gene expression [17]. In Arabidopsis, three MAPKs (MPK3, MPK4 and MPK6) have been implicated in defense against pathogens [18,19,20]. MPK6 functions as substrate of at least four MAPK kinases (MKK2, MKK3, MKK4 and MKK5) in response to different stimuli, including developmental, microbial or environ- mental cues. Once phosphorylated, MPK6 activates several transcriptional regulators, such as members of the WRKY, MYC and ERF gene families. Particularly, but not exclusively, the MKK3-MPK6 cascade is activated in response to JA and both, positively and negatively regulates the expression of JA-related genes [17,21]. Concordantly, the MKK3-knockout mutant mkk3 and coi1 had an altered activation of MPK6 in response to JA. Moreover, mutations in MPK6 compromise the accumulation of antifungal phytotoxin camalexin in response to infection with Botrytis cinerea [17,22]. Alkamide-Regulated Transcriptional Networks An additional class of lipids conserved among different kingdoms with signaling functions in plants is the fatty acid amides group, including the plant-, fungal- or animal-produced N- acylamides (alkamides), N-acylethanolamines (NAEs), and the N- acyl-L-homoserine lactones synthesized by Gram-negative bacte- ria. Compounds representative of these three classes of lipids have been shown to modulate seedling development in Arabidopsis and to affect plant biomass production in a dose-dependent way, indicating a strong biological activity [23,24,25]. NAEs are compounds with aminoalcohol linked as an amide to the fatty acid, which accumulate in seeds of higher plants, including cotton, corn, soybean, tomato, pea and Arabidopsis, and decrease during germination [26]. Pioneering research on fatty acid amides showed that NAE production in plants is associated to defense responses. NAE 14:0 accumulates in tobacco leaves treated with fungal elicitors, and exogenous application of this NAE is able to induce expression of defense-related genes [27]. Moreover, the ectopic overexpression of a plant fatty acid amide hydrolase (FAAH), an enzyme that degrades NAEs, renders Arabidopsis plants more susceptible to both host and non-host bacterial pathogens [28]. N-acyl-L-homoserine lactones (AHLs) are structural analogs of NAEs and alkamides, that are produced by Gram negative bacteria and participate in the cell-to-cell communication process commonly referred to as quorum-sensing (QS). Interestingly, plants have the genetic machinery to perceive and respond to AHLs. The presence of AHL-producing bacteria in the rhizo- sphere of tomato induces SA- and JA-dependent defense responses, conferring resistance to the fungal pathogen Alternaria alternata [29]. Moreover, the application of purified AHLs to Medicago truncatula and Arabidopsis plants results in differential transcriptional changes in roots and shoots, affecting expression of genes potentially involved in immune responses and development [30,31]. Interestingly, FAAH knockouts and overexpressors Arabidopsis lines are more sensitive and tolerant, respectively, to the root inhibitory effects of AHLs, in a similar fashion to their response to exogenous NAEs and alkamides, while an alkamide resistant mutant termed decanamide resistant root 1 (drr1) showed decreased root responses to alkamides and AHLs [25,32]. Alkamides comprise over 200 related compounds and they have been found in several plant families: Aristolochiaceae, Asteraceae, Brassicaceae, Convolvulaceae, Euphorbiaceae, Menispermaceae, Piperaceae, Poaceae, Rutaceae, and Solanaceae, reviewed in [33,34]. Some traditional medicinal plants produce these second- ary metabolites during their life cycle in response to several stress conditions to mediate, among other processes, plant chemical defense against plant competitors or microbial and herbivorous predators [35]. Several species from the genus Echinacea accumu- late unsaturated alkamides ranging from 12 to 18 carbon atoms in response to JAs [36,37]. These unsatured alkamides are also active in mammals; they activate immune responses in alveolar macrophages from rats, in concert with a sustained production of NO, a canonical messenger in plant and animal defense responses [38,39]. Alkamides have also been identified in insects, such as N-linolenoyl-L-glutamine, present in oral secretions of the tobacco hornworm (Manduca sexta), which is able to elicit defensive responses in plants by inducing volatile chemicals that attract predators and parasites of the attacker [40]. The wound-induced JA production is amplified by application of these oral secretions in Nicotiana attenuata leaves, indicating a reciprocal crosstalk between JAs- and alkamides-related signal pathways [41]. To date, however, there is no direct evidence as to whether alkamides can switch JA production and its transcriptional targets. The short-chain alkamide affinin from the ‘‘gold-root’’ Heliopsis longipes has been reported to have antimicrobial activity inhibiting PLoS ONE | www.plosone.org 2 November 2011 | Volume 6 | Issue 11 | e27251