Carlos L. Calderón-Vázquez

Analysis of Gene Expression and Physiological Responses in Three Mexican Maize Landraces under Drought Stress and Recovery Irrigation

Background Drought is one of the major constraints for plant productivity worldwide. Different mechanisms of drought-tolerance have been reported for several plant species including maize. However, the differences in global gene expression between drought-tolerant and susceptible genotypes and their relationship to physiological adaptations to drought are largely unknown. The study of the differences in global gene expression between tolerant and susceptible genotypes could provide important information to design more efficient breeding programs to produce maize varieties better adapted to water limiting conditions. Methodology/Principal Findings Changes in physiological responses and gene expression patterns were studied under drought stress and recovery in three Mexican maize landraces which included two drought tolerant (Cajete criollo and Michoacán 21) and one susceptible (85-2) genotypes. Photosynthesis, stomatal conductance, soil and leaf water potentials were monitored throughout the experiment and microarray analysis was carried out on transcripts obtained at 10 and 17 days following application of stress and after recovery irrigation. The two tolerant genotypes show more drastic changes in global gene expression which correlate with different physiological mechanisms of adaptation to drought. Differences in the kinetics and number of up- and down-regulated genes were observed between the tolerant and susceptible maize genotypes, as well as differences between the two tolerant genotypes. Interestingly, the most dramatic differences between the tolerant and susceptible genotypes were observed during recovery irrigation, suggesting that the tolerant genotypes activate mechanisms that allow more efficient recovery after a severe drought. Conclusions/Significance A correlation between levels of photosynthesis and transcription under stress was observed and differences in the number, type and expression levels of transcription factor families were also identified under drought and recovery between the three maize landraces. Gene expression analysis suggests that the drought tolerant landraces have a greater capacity to rapidly modulate more genes under drought and recovery in comparison to the susceptible landrace. Modulation of a greater number of differentially expressed genes of different TF gene families is an important characteristic of the tolerant genotypes. Finally, important differences were also noted between the tolerant landraces that underlie different mechanisms of achieving tolerance.

Transcript profiling of Zea mays roots reveals gene responses to phosphate deficiency at the plant- and species-specific levels

Maize (Zea mays) is the most widely cultivated crop around the world; however, it is commonly affected by phosphate (Pi) deficiency in many regions, particularly in acid and alkaline soils of developing countries. To cope with Pi deficiency, plants have evolved a large number of developmental and biochemical adaptations; however, for maize, the underlying molecular basis of these responses is still unknown. In this work, the transcriptional response of maize roots to Pi starvation at 1, 3, 6, and 10 d after the onset of Pi deprivation was assessed. The investigation revealed a total of 1179 Pi-responsive genes, of which 820 and 363 genes were found to be either up- or down-regulated, respectively, by 2-fold or more. Pi-responsive genes were found to be involved in various metabolic, signal transduction, and developmental gene networks. A large set of transcription factors, which may be potential targets for crop breeding, was identified. In addition, gene expression profiles and changes in specific metabolites were also correlated. The results show that several dicotyledonous plant responses to Pi starvation are conserved in maize, but that some genetic responses appear to be more specific and that Pi deficiency leads to a shift in the recycling of internal Pi in maize roots. Ultimately, this work provides a more comprehensive view of Pi-responses in a model for economically important cereals and also sets a framework to produce Pi-specific maize microarrays to study the changes in global gene expression between Pi-efficient and Pi-inefficient maize genotypes.

Phosphate Deprivation in Maize: Genetics and Genomics

Plants acquire phosphorus (P) from the soil in order to reach the intracellular concentrations necessary for growth and reproduction. To prevent P starvation, both monocotyledonous and dicotyledonous plants have evolved well-regulated systems for inorganic phosphate (Pi) scavenging, acquisition, and

Phosphate deprivation responses in maize: genetics and genomics

Plants acquire phosphorus (P) from the soil in order to reach the intracellular concentrations necessary for growth and reproduction. To prevent P starvation, both monocotyledonous and dicotyledonous plants have evolved well-regulated systems for inorganic phosphate (Pi) scavenging, acquisition, and

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.

Genome distribution and validation of novel microsatellite markers of Fusarium verticillioides and their transferability to other Fusarium species

Improved population studies in the fungus Fusarium verticillioides require the development of reliable microsatellite markers. Here we report a set of ten microsatellite loci that can be used for genetic diversity analyses in F. verticillioides, and are equally applicable to other fungi, especially those belonging to the Gibberella fujikuroi clade.

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.

Maize Under Phosphate Limitation

Phosphorus is one of the least available macronutrient for plants in soils, and is therefore considered to be a major constraint for plant growth and crop productivity. As a consequence, plants evolved a number a biochemical and developmental adaptations to combat this deficiency. In maize, such adaptations are based on a wide spectrum of mechanisms needed to increase the P uptake, assimilation and use efficiency. These mechanisms frequently act in parallel with a morphological plasticity in root architecture. Such adaptive strategies have been reported in several phosphate efficient genotypes, identified and selected from the large natural and man-made diversity found within the maize species. Advances in research have now begun to identify at the molecular level the adaptations evolved by maize to cope with Pi limitation. In this chapter we summarize the current research on the development of tolerant genotypes and the physiological, biochemical and molecular adaptations associated with low phosphate availability. Such knowledge will allows us to identify putative targets for breeding and opens the possibility to improve nutrient acquisition and productivity in maize and other cereals.

PvLOX2 silencing in common bean roots impairs arbuscular mycorrhiza-induced resistance without affecting symbiosis establishment

The arbuscular mycorrhizal (AM) symbiosis is an intimate association between specific soil-borne fungi and the roots of most land plants. AM colonisation elicits an enhanced defence resistance against pathogens, known as mycorrhizal-induced resistance (MIR). This mechanism locally and systemically sensitises plant tissues to boost their basal defence response. Although a role for oxylipins in MIR has been proposed, it has not yet been experimentally confirmed. In this study, when the common bean (Phaseolus vulgaris L.) lipoxygenase PvLOX2 was silenced in roots of composite plants, leaves of silenced plants lost their capacity to exhibit MIR against the foliar pathogen Sclerotinia sclerotiorum, even though they were colonised normally. PvLOX6, a LOX gene family member, is involved in JA biosynthesis in the common bean. Downregulation of PvLOX2 and PvLOX6 in leaves of PvLOX2 root-silenced plants coincides with the loss of MIR, suggesting that these genes could be involved in the onset and spreading of the mycorrhiza-induced defence response.

Evaluación de la Virulencia de Steinernema riobrave y Rhabditis blumi contra Larvas del Tercer Instar de Spodoptera frugiperda1

Resumen. Se evaluó la virulencia de los nematodos Steinernema riobrave (Poinar y Raulston, 1994) y la de un aislamiento nativo de Rhabditis blumi (Sudhaus, 1974) contra gusano cogollero del maíz Spodoptera frugiperda (J.E. Smith). Ambos nematodos fueron usados para inocular larvas del tercer instar de desarrollo concentraciones de 100, 250, y 500 juveniles infectivos (JI) por larva y determinar la mortalidad de las larvas cada 24 h durante 7 días. El nematodo S. riobrave causó 90% de mortalidad a 500 JI, 96 h después de la inoculación, mientras que con la especie R. blumi no hubo mortalidad de larvas a las concentraciones y tiempo de evaluación. El nematodo S. riobrave tuvo alta virulencia, por lo que esta especie se consideran viable para usarse en una prueba de efectividad para el control de S. frugiperda en campo.