Alfonso Méndez-Bravo

Serotonin, a Tryptophan-Derived Signal Conserved in Plants and Animals, Regulates Root System Architecture Probably Acting as a Natural Auxin Inhibitor in Arabidopsis thaliana

Serotonin (5-hydroxytryptamine) is a well-known neurotransmitter in mammals and is widely distributed in plants. This compound is synthesized from tryptophan and shares structural similarity with IAA. To date, little is known about the morphological, physiological and molecular responses of plants to serotonin. In this study, we characterized the effects of serotonin on growth and development in Arabidopsis thaliana seedlings. Gas chromatography-mass spectrometry (GC-MS) analysis showed that plants are able to take up serotonin from the growth medium, which coincided with greatly stimulated lateral root development at concentrations from 10 to 160 μM. In contrast, higher doses of serotonin repressed lateral root growth, primary root growth and root hair development, but stimulated adventitious root formation. To investigate the role of serotonin in modulating auxin responses, we performed experiments using transgenic Arabidopsis lines expressing the auxin-responsive marker constructs DR5:uidA, BA3:uidA and HS::AXR3NT-GUS, as well as a variety of Arabidopsis mutants defective at the AUX1, AXR1, AXR2 and AXR4 auxin-related loci. We found that serotonin strongly inhibited both DR5:uidA and BA3:uidA gene expression in primary and adventitious roots and in lateral root primordia. This compound also abolished the effects of IAA or naphthaleneacetic acid on auxin-regulated developmental and genetic responses, indicating an anti-auxin activity in the plant. Mutant analysis further showed that lateral root induction elicited by serotonin was independent of the AUX1 and AXR4 loci but required AXR1 and AXR2. Our results show that serotonin regulates root development probably by acting as a natural auxin inhibitor.

Nitric Oxide is Involved in Alkamide-Induced Lateral Root Development in Arabidopsis

Alkamides are small bioactive lipid signals with a wide distribution in plants. In this report, the role of nitric oxide (NO) in the alterations induced by N-isobutyl decanamide on the Arabidopsis (Arabidopsis thaliana) root system architecture (RSA) was investigated. We first compared the effects of N-isobutyl decanamide and NO donors sodium nitropruside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) on root morphogenetic processes. Both N-isobutyl decanamide and NO donors modulated RSA in a similar way and in a dose-dependent manner, inhibiting primary root growth and promoting lateral root primordia (LRP) formation. RSA alterations induced by N-isobutyl decanamide correlated with NO accumulation in the primary root tip and in developing lateral roots. Morphogenetic effects of N-isobutyl decanamide decreased when NO scavengers were supplied to alkamide-treated seedlings. N-Isobutyl decanamide-regulated root architectural changes were also investigated in mutants defective in NO biosynthesis, nia1 nia2, and NO signalling, Atnoa1, and in the alkamide-resistant mutant drr1. The nia1 nia2 and Atnoa1 mutants were indistinguishable in primary root growth inhibition by the alkamide when compared with wild-type (WT) seedlings, but showed reduced lateral root responses. The drr1 mutant was less sensitive in both primary root growth inhibition and LRP induction by NO donors than WT seedlings. Detailed DR5:uidA and BA3:uidA marker analysis showed that N-isobutyl decanamide and its interacting signals jasmonic acid and NO act downstream or independently of auxin-responsive gene expression to promote LRP formation. Our results provide compelling evidence that NO is an intermediate in alkamide signaling mediating RSA adjustment in Arabidopsis.

Cytokinin receptors are involved in alkamide regulation of root and shoot development in Arabidopsis.

Alkamides and N-acilethanolamides are a class of lipid compounds related to animal endocannabinoids of wide distribution in plants. We investigated the structural features required for alkamides to regulate plant development by comparing the root responses of Arabidopsis (Arabidopsis thaliana) seedlings to a range of natural and synthetic compounds. The length of the acyl chain and the amide moiety were found to play a crucial role in their biological activity. From the different compounds tested, N-isobutyl decanamide, a small saturated alkamide, was found to be the most active in regulating primary root growth and lateral root formation. Proliferative-promoting activity of alkamide treatment was evidenced by formation of callus-like structures in primary roots, ectopic blades along petioles of rosette leaves, and disorganized tumorous tissue originating from the leaf lamina. Ectopic organ formation by N-isobutyl decanamide treatment was related to altered expression of the cell division marker CycB1:uidA and an enhanced expression of the cytokinin-inducible marker ARR5:uidA both in roots and in shoots. The involvement of cytokinins in mediating the observed activity of alkamides was tested using Arabidopsis mutants lacking one, two, or three of the putative cytokinin receptors CRE1, AHK2, and AHK3. The triple cytokinin receptor mutant was insensitive to N-isobutyl decanamide treatment, showing absence of callus-like structures in roots, the lack of lateral root proliferation, and absence of ectopic outgrowths in leaves under elevated levels of this alkamide. Taken together our results suggest that alkamides and N-acylethanolamides may belong to a class of endogenous signaling compounds that interact with a cytokinin-signaling pathway to control meristematic activity and differentiation processes during plant development.

Characterization of drr1, an alkamide resistant mutant of Arabidopsis reveals an important role for small lipid amides in lateral root development and plant senescence

Alkamides belong to a class of small lipid signals of wide distribution in plants, which are structurally related to the bacterial quorum-sensing signals N-acyl-l-homoserine lactones. Arabidopsis (Arabidopsis thaliana) seedlings display a number of root developmental responses to alkamides, including primary root growth inhibition and greater formation of lateral roots. To gain insight into the regulatory mechanisms by which these compounds alter plant development, we performed a mutant screen for identifying Arabidopsis mutants that fail to inhibit primary root growth when grown under a high concentration of N-isobutyl decanamide. A recessive N-isobutyl decanamide-resistant mutant (decanamide resistant root [drr1]) was isolated because of its continued primary root growth and reduced lateral root formation in response to this alkamide. Detailed characterization of lateral root primordia development in the wild type and drr1 mutants revealed that DRR1 is required at an early stage of pericycle cell activation to form lateral root primordia in response to both N-isobutyl decanamide and N-decanoyl-l-homoserine lactone, a highly active bacterial quorum-sensing signal. Exogenously supplied auxin similarly inhibited primary root growth and promoted lateral root formation in wild-type and drr1 seedlings, suggesting that alkamides and auxin act by different mechanisms to alter root system architecture. When grown both in vitro and in soil, drr1 mutants showed dramatically increased longevity and reduced hormone- and age-dependent senescence, which were related to reduced lateral root formation when exposed to stimulatory concentrations of jasmonic acid. Taken together, our results provide genetic evidence indicating that alkamides and N-acyl-l-homoserine lactones can be perceived by plants to modulate root architecture and senescence-related processes possibly by interacting with jasmonic acid signaling.

Alkamides Activate Jasmonic Acid Biosynthesis and Signaling Pathways and Confer Resistance to Botrytis cinerea in Arabidopsis thaliana

Alkamides are fatty acid amides of wide distribution in plants, structurally related to N-acyl-L-homoserine lactones (AHLs) from Gram-negative bacteria and to N- acylethanolamines (NAEs) from plants and mammals. Global analysis of gene expression changes in Arabidopsis thaliana in response to N-isobutyl decanamide, the most highly active alkamide identified to date, revealed an overrepresentation of defense-responsive transcriptional networks. In particular, genes encoding enzymes for jasmonic acid (JA) biosynthesis increased their expression, which occurred in parallel with JA, nitric oxide (NO) and H2O2 accumulation. The activity of the alkamide to confer resistance against the necrotizing fungus Botrytis cinerea was tested by inoculating Arabidopsis detached leaves with conidiospores and evaluating disease symptoms and fungal proliferation. N-isobutyl decanamide application significantly reduced necrosis caused by the pathogen and inhibited fungal proliferation. Arabidopsis mutants jar1 and coi1 altered in JA signaling and a MAP kinase mutant (mpk6), unlike salicylic acid- (SA) related mutant eds16/sid2-1, were unable to defend from fungal attack even when N-isobutyl decanamide was supplied, indicating that alkamides could modulate some necrotrophic-associated defense responses through JA-dependent and MPK6-regulated signaling pathways. Our results suggest a role of alkamides in plant immunity induction.

Pyocyanin, a Virulence Factor Produced by Pseudomonas aeruginosa, Alters Root Development Through Reactive Oxygen Species and Ethylene Signaling in Arabidopsis

Pyocyanin acts as a virulence factor in Pseudomonas aeruginosa, a plant and animal pathogen. In this study, we evaluated the effect of pyocyanin on growth and development of Arabidopsis seedlings. Root inoculation with P. aeruginosa PAO1 strain inhibited primary root growth in wild-type (WT) Arabidopsis seedlings. In contrast, single lasI- and double rhlI-/lasI- mutants of P. aeruginosa defective in pyocyanin production showed decreased root growth inhibition concomitant with an increased phytostimulation. Treatment with pyocyanin modulates root system architecture, inhibiting primary root growth and promoting lateral root and root hair formation without affecting meristem viability or causing cell death. These effects correlated with altered proportions of hydrogen peroxide and superoxide in root tips and with an inhibition of cell division and elongation. Mutant analyses showed that pyocyanin modulation of root growth was likely independent of auxin, cytokinin, and abscisic acid but required ethylene signaling because the Arabidopsis etr1-1, ein2-1, and ein3-1 ethylene-related mutants were less sensitive to pyocyanin-induced root stoppage and reactive oxygen species (ROS) distribution. Our findings suggest that pyocyanin is an important factor modulating the interplay between ROS production and root system architecture by an ethylene-dependent signaling.

Deep sequencing of the Mexican avocado transcriptome, an ancient angiosperm with a high content of fatty acids

BackgroundAvocado (Persea americana) is an economically important tropical fruit considered to be a good source of fatty acids. Despite its importance, the molecular and cellular characterization of biochemical and developmental processes in avocado is limited due to the lack of transcriptome and genomic information.ResultsThe transcriptomes of seeds, roots, stems, leaves, aerial buds and flowers were determined using different sequencing platforms. Additionally, the transcriptomes of three different stages of fruit ripening (pre-climacteric, climacteric and post-climacteric) were also analyzed. The analysis of the RNAseqatlas presented here reveals strong differences in gene expression patterns between different organs, especially between root and flower, but also reveals similarities among the gene expression patterns in other organs, such as stem, leaves and aerial buds (vegetative organs) or seed and fruit (storage organs). Important regulators, functional categories, and differentially expressed genes involved in avocado fruit ripening were identified. Additionally, to demonstrate the utility of the avocado gene expression atlas, we investigated the expression patterns of genes implicated in fatty acid metabolism and fruit ripening.ConclusionsA description of transcriptomic changes occurring during fruit ripening was obtained in Mexican avocado, contributing to a dynamic view of the expression patterns of genes involved in fatty acid biosynthesis and the fruit ripening process.

An improved, low-cost, hydroponic system for growing Arabidopsis and other plant species under aseptic conditions

BackgroundHydroponics is a plant growth system that provides a more precise control of growth media composition. Several hydroponic systems have been reported for Arabidopsis and other model plants. The ease of system set up, cost of the growth system and flexibility to characterize and harvest plant material are features continually improved in new hydroponic system reported.ResultsWe developed a hydroponic culture system for Arabidopsis and other model plants. This low cost, proficient, and novel system is based on recyclable and sterilizable plastic containers, which are readily available from local suppliers. Our system allows a large-scale manipulation of seedlings. It adapts to different growing treatments and has an extended growth window until adult plants are established. The novel seed-holder also facilitates the transfer and harvest of seedlings. Here we report the use of our hydroponic system to analyze transcriptomic responses of Arabidopsis to nutriment availability and plant/pathogen interactions.ConclusionsThe efficiency and functionality of our proposed hydroponic system is demonstrated in nutrient deficiency and pathogenesis experiments. Hydroponically grown Arabidopsis seedlings under long-time inorganic phosphate (Pi) deficiency showed typical changes in root architecture and high expression of marker genes involved in signaling and Pi recycling. Genome-wide transcriptional analysis of gene expression of Arabidopsis roots depleted of Pi by short time periods indicates that genes related to general stress are up-regulated before those specific to Pi signaling and metabolism. Our hydroponic system also proved useful for conducting pathogenesis essays, revealing early transcriptional activation of pathogenesis-related genes.

Amino Compound-Containing Lipids: a Novel Class of Signals Regulating Plant Development

Plant growth and development are driven by the integration of a vast number of signals including volatile compounds, small organic molecules, peptides, steroids and lipids. Among these, amino-containing signalling lipids such as alkamides and N-acyl ethanolamines (NAEs) have emerged as important regulators of cellular processes, including cell proliferation, growth and differentiation. Manipulation in the concentrations of alkamides and NAEs in plants by pharmacological, mutational and transgenic approaches affect morphogenetic processes including seed germination and post-embryonic shoot and root development. Further evidence for a role of these compounds in regulating physiological processes is supported by their occurrence in a wide range of plant species, their selective accumulation and rapid metabolism in response to developmental transitions, and by the recent identification of the enzymes that metabolize NAEs. Moreover, signal transduction cascades involving abscisic acid, cytokinins and nitric oxide have been found to interact with alkamides and NAEs, highlighting the importance of crosstalk between these novel small lipids and other classic signals for plant growth regulation. The discovery that N-acyl homoserine lactones (AHLs), a class of bacterial quorum-sensing signals structurally related to alkamides, can be perceived by plants opens the possibility that acylamides could be also involved in plant–bacterial interactions.