Lourdes Georgina Iglesias-Andreu

Transcriptome analysis of Arabidopsis roots treated with signaling compounds: a focus on signal transduction, metabolic regulation and secretion

Gene expression in response to signaling molecules has been well studied in the leaves of the model plant species Arabidopsis thaliana. However, knowledge of gene expression and metabolic regulation at the root level is limited. Here, the signaling compounds salicylic acid (SA), methyl jasmonate (MeJA) and nitric oxide (NO) were applied exogenously to induce various defense responses in roots, and their effect was studied using a combination of genomic, molecular and biochemical approaches. Genes involved in defense signaling/activation, cellular redox state, metabolism, transcription factors and membrane transport were altered in expression following treatment with SA, MeJA and NO. In addition, it was found that SA-, MeJA- and NO-elicited roots increased the root exudation of phytochemicals compared with the roots of nontreated control plants. Transport systems likely to be involved in the root exudation of phytochemicals, including the MATE, ABC, MFS, amino acid, sugar and inorganic solute transporters, showed altered expression profiles in response to treatments. Overall, significant differences were found in the signaling compound-elicited expression profiles of genes in roots vs those in leaves. These differences could be correlated to the underground nature of roots and their exposure to higher microbial inoculum rates under natural conditions.

Evaluation of different temporary immersion systems (BIT®, BIG, and RITA®) in the micropropagation of Vanilla planifolia Jacks

The cultivation of Vanilla planifolia is of great economic importance because vanillin, a chemical valued in the food and cosmetics industry, is extracted from its pods. The conventional propagation of this plant is limited by the low viability of its seeds and the very low germination rate. For this reason, in vitro micropropagation techniques using temporary immersion systems (TIS) represent an alternative propagation mechanism. This work assessed three different bioreactor systems in two different micropropagation phases (multiplication and rooting) of V. planifolia: Temporary Immersion Bioreactors (BIT®), Gravity Immersion Bioreactors (BIG), and Recipient for Automated Temporary Immersion (RITA®). A higher number of shoots/explant were observed in the multiplication phase in BIT® systems (18.06 shoots/explant), followed by RITA® (12.77) and BIG (6.83). In the rooting phase, a higher number of longer roots were obtained in BIT® compared with BIG and RITA®. However, higher chlorophyll content was observed in BIG, followed by RITA® and BIT®. A 100% survival was obtained in vitro micropropagated plantlets in BIT®, exceeding the survival rate observed in RITA® and BIG. In general, our findings confirm the utility of BIT® systems in the optimization of the commercial micropropagation of this species. Furthermore, this system reduces the costs associated with the use of RITA® systems.

The Effect of Light Quality on Growth and Development of In Vitro Plantlet of Stevia rebaudiana Bertoni

Abstract Fluorescent lamps are the most commonly used light source for the in vitro culture of various plant species. However, there are other sources of illumination, such as light-emitting diodes (LEDs), which have proven to be more efficient for in vitro culture. In the present study, we evaluated the effect of LEDs on the in vitro morphogenesis, proliferation of shoots, growth and rooting of Stevia rebaudiana Bertoni. For that, five different sources of light were tested under a 16-h photoperiod: fluorescent lamps (Fl), white LEDs (W), red LEDs (R), blue LEDs (B) and a combination of blue and red LEDs (B/R, 1:1). The proliferation rate was higher with R LEDs compared with Fl light, although shoots have a lower length under R LEDs. Under B/R LEDs, maximum shoot elongation was obtained. During rooting, LEDs did not improve the rooting of shoots but increased the content of photosynthetic pigments, which contributed to the acclimation process of in vitro plantlets. Our results revealed that the spectrum of different light sources produced different effects during the in vitro culture of S. rebaudiana.

Vanilla rhizobacteria as antagonists against Fusarium oxysporum f. sp. vanillae.

Pathogens such as Fusarium oxysporum strongly affect the health of various agricultural crops like vanilla. However, despite significant economic losses caused by this pathogen there is no efficient method for its control. Therefore, we propose using rhizobacteria obtained from vanilla roots against F. oxysporum f. sp. vanillae. The results showed that there was no positive correlation between the antagonism expressed under in vitro conditions and those expressed under greenhouse conditions. The 16S rDNA gene analysis indicated that the bacterial genera tested corresponded to Sphingobacterium, Staphylococcus, Serratia, Psychrobacter, Pseudomonas and Stenotrophomonas. The in vitro antifungal activity was evaluated using three culture media (Potato Dextrose Agar, Nutrient Agar and Czapek) using the empty box technique (antagonism). Isolates of Staphylococcus xylosus BAC-JAG15, Serratia sp. BAC-JAG4 and Stenotrophomonas sp. BAC-JAG1 showed 90% in vitro antagonism against F. oxysporum in the three media tested. In the greenhouse evaluation, plants treated with these isolates initially showed symptoms of chlorosis without developing characteristic symptoms of disease produced by F. oxysporum f. sp. vanillae. This demonstrates protection provided by rhizobacteria against infection from F. oxysporum f. sp. vanillae in vanilla plants.

Extinction Risk of Zamia inermis (Zamiaceae): A Genetic Approach for the Conservation of Its Single Natural Population

Zamia inermis, a narrowly endemic cycad, has been classified under the International Union for Conservation of Nature Red List as critically endangered on the basis of a 75% population decline over past 50 yr. There is only one known population occupying an area of less than 10 km2, with 654 individuals with extremely low seed production and recruitment. This study compares the genetic diversity of the only known in situ population of Z. inermis and one ex situ population established 5 yr ago by a local community running a rural backyard nursery. We aimed to assess the current conservation status and to propose a more efficient management strategy. Our results by using a total of 10 simple sequence repeat loci showed a low observed heterozygosity (0.151 ± 0.075) in comparison to other New World cycads. Significant differences were found between ex situ population and wild populations (differentiation index FST1, 156 = 0.734, P < 0.001), with lower variation within (27%) than among (73%) populations. Zamia inermis presented the lowest genetic diversity to be reported for Mexican cycads. The ex situ population had a lower variation than wild population and thus does not fully represent the genetic diversity of the species. This suggests that there was a poor representation of genetic diversity among the seed collected to establish the ex situ population. Alternative conservation strategies are suggested.

Evaluation of molecular variability in germplasm of vanilla ( Vanilla planifolia G. Jackson in Andrews) in Southeast Mexico: implications for genetic improvement and conservation

Molecular variability of vanilla ( Vanilla planifolia ) and three wild species was assessed to explore the possible sources of variation that can be used for crop improvement. A total of 154 ISSR loci were analysed by the UPGMA, assignment tests of individuals (STRUCTURE) and indices of genetic diversity. The assignment tests were done at two levels: first considering the four species and then only the accessions of V. planifolia . The molecular analysis indicated 99.3% polymorphism among all species and 70.45% within V. planifolia . The UPGMA showed the separation of these four species into three groups and grouped V. planifolia accessions into three subgroups. The more genetically differentiated accessions were of the Rayada morphotype and a wild accession was from Oaxaca, followed by a wild accession from Quintana Roo; all the commercial accessions of V. planifolia (Mansa morphotype) were grouped together. The STRUCTURE analysis differentiated between V. planifolia and the three wild species, and among the accessions of the Mansa and Rayada morphotypes and the wild accessions. The STRUCTURE analysis also indicated the presence of mixed individuals. These results are of great importance since the accessions of V. planifolia that are genetically more differentiated are the most threatened due to the scarcity of these individuals, the destruction of habitat and replacement by the commercial morphotype. These individuals should be salvaged and used to expand the genetic background of vanilla.

Fine-Scale Genetic Structure of Zamia furfuracea: Variation with Life-Cycle Stages

Fine-scale spatial genetic structure (SGS) analysis has proved to be a useful tool to establish the distribution of genetic variability between individuals and how these patterns are affected by microenvironmental conditions, associations with pollinators and dispersers, and sex ratio. In this study, the correlation between the fine-scale SGS of a population of Zamia furfuracea L. fil. and its dependence on the patterns of spatial aggregation between categories of life cycle and the proportion of males and females was determined by using intersimple sequence repeat markers. Results showed an aggregation pattern dependent on reproductive adults of up to 10 m; however, dependence on sex was restricted to only 3 m, suggesting limited pollen and seed dispersal. Gene neighborhoods did not exceed 10 m, with three well-defined families within the population. The small size of the neighborhoods, high mortality rate of seedlings, and loss of genetic variability in the juvenile category suggest that this population is severely affected. Our results contribute to the understanding of genetic and spatial dynamics in natural populations of cycads. Such information should be considered for the implementation of ex situ population-management programs.

Detection of Maize Bushy Stunt Phytoplasma in Leafhoppers Collected in Native Corn Crops Grown at High Elevations in Southeast Mexico

Abstract Phytoplasmas are wall-less bacteria, unculturable in vitro, and transmitted primarily by leafhoppers (Cicadellidae). Maize bushy stunt disease has been linked to phytoplasmas belonging to the16SrI-B subgroup and vectored by leafhoppers in the genus Dalbulus spp. (Hemiptera: Cicadellidae). The recent detection of maize bushy stunt affecting native corn, maize, in the southeast highlands of Mexico motivated the survey to determine which leafhoppers were associated with this crop during the 2013-2014 growing season. We detected 7 leafhopper genera in native corn cultivated 2,400 meters above sea level (masl), with 4 of these genera reported for the first time in corn. Based on external morphology and male genitalia, we identified Idiodonus wickhami (Ball) (Hemiptera: Cicadellidae), Amblysellus grex (Oman) (Hemiptera: Cicadellidae), Empoasca fabae (Harris) (Hemiptera: Cicadellidae), Macrosteles quadrilineatus (Forbes) (Hemiptera: Cicadellidae), and Dalbulus elimatus (Ball) (Hemiptera: Cicadellidae). We were not able to identify the leafhopper genera Graphocephala (Hemiptera: Cicadellidae) and Erythridula (Hemiptera: Cicadellidae) to species because of a lack of male leafhoppers. Nymphal stages of I. wickhami also were identified using taxonomic and molecular tools. The presence of adults and nymphs of I. wickhami in the crop suggest that native corn grown in the southeast highlands of Mexico is a feeding and reproductive host for I. wickhami. Moreover, I. wickhami was found infected with 16SrI-B strain maize bushy stunt-Ver while D. elimatus, a well-known maize bushy stunt phytoplasma vector, was found infected with the 16SrI-B strain maize bushy stunt-Pueb.

Preliminary molecular detection of the somatic embryogenesis receptor-like kinase (VpSERK) and knotted-like homeobox (VpKNOX1) genes during in vitro morphogenesis of Vanilla planifolia Jacks

This work aimed to evaluate the embryogenic competence of different tissues from different stages (friable callus, bud-regenerating callus, and whole buds) of Vanilla planifolia, through the molecular detection of the somatic embryogenesis receptor-like kinase (VpSERK) and knotted-like homeobox (VpKNOX1) genes. RNA was extracted with Trizol®, cDNA was obtained, and the studied transcripts were amplified. Using non-specific primers, VpSERK and VpSTM gene expression was detected in the three stages evaluated. This study might contribute to providing an explanation for the recalcitrance of this Vanilla species to somatic embryogenesis.