Detection of 16SrIV-A phytoplasma DNA in Colpoptera sp. (Hemiptera: Nogodinidae) insects in Yucatan Peninsula, Mexico.

Lethal yellowing (LY) is a disease that affects coconut and other palm species. It is associated to phytoplasmas of the group 16SrIV and the only reported insect vector for this pathogen so far is Haplaxius crudus. H. crudus is present in Mexico and has been associated to 16SrIV phytoplasmas, however, it was not detectable during a LY outbreak in the coast of Yucatan, Mexico, suggesting the existence of other vector species. To test this hypothesis a survey of insects was carried out and a total of 3074 insects were captured during a year of monthly sampling. Ten taxonomic orders were identified in this sample, Hemiptera being the most abundant (N=2094), and these were classified into nine families. The leafhopper Colpoptera sp. from to the Nogodinidae family was de most abundant representing 56% of the total number of insects sampled and 23% of these samples resulted positive for LY phytoplasma by PCR detection. The BLAST comparison, virtual RFLP and phylogenetic analyses of the sequenced amplicons relate the detected phytoplasma to the subgroup 16SrIV-A. The findings presented herein suggest that Colpoptera sp. could be considered as a new putative vector of the LY-causing phytoplasmas in Mexico and a candidate for further research.

Transcriptome analysis reveals key defense-related genes upon SA induction in Cocos nucifera L.

BACKGROUND: Salicylic acid (SA) is an important regulator of genes involved in plant defense and pathogen-triggered systemic acquired resistance (SAR). Coconut is an important crop affected by several pathogens. Reported evidence suggests SA involvement in defense responses, including SAR in coconut. OBJECTIVE: To identified differentially expressed genes in leaf and root tissues of coconut plantlets, as a result of SA, that might be involved in coconut defense responses. METHODS: Comparative transcriptomic analysis by RNA-Seq of leaf and root tissues from in vitro coconut plantlets unexposed and exposed to SA 2.5 mM for 48 h. And in silico validation of gene expression by qRT-PCR. RESULTS: We identified 4615 and 3940 differentially expressed unigenes (DEUs) in leaf and root tissues respectively. Our GO analysis showed functional categories related to the induction of defense responses, such as "systemic acquired resistance" and highly enriched hormone categories, such as abscisic acid. The most abundant KEGG pathway in our results was "Biosynthesis of antibiotics". Our findings support that exogenous application of SA to plantlets induced the activation of PRs, RGAs, ICS2, NLTP2, PER4, TRXM and some WRKYs mediated by NPR1-dependent pathways. Also, we found DEUs, such as BZR1, HSL1, and WHY2 that support that SA could regulate defense-related genes through NPR1-independent pathways. CONCLUSION: The present study of massive data analysis carried out on coconut plantlets exposed to SA, generates valuable information that increases our understanding of defense molecular mechanisms in coconut and open new venues for research for the improvement of management of coconut diseases.

Genes coding for transporters showed a rapid and sharp increase in their expression in response to lead, in the aquatic fern (Salvinia minima Baker).

Salvinia minima was assessed for its ability to accumulate lead (Pb) by exposing it to concentrations of 40µM Pb(NO3)2 during 24h. At the same time, the expression levels were quantified, of four genes coding for transporters: SmABCC (ABCC-MRP), SmATPase (ATPase-P3A), SmNhaD (Type-Na+/H+) and SmABCG (ABCG-WBC). In the absence of lead, S. minima had very low expression of those genes, when plants were exposed to the metal however, those genes showed a rapid (in just three hours or less) and sharp increase (up to 60 times) in their expression, particularly the SmNhaD (Type-Na+/H+) gene. This sharp increase in expression levels of the genes studied, occurred at the same time that the plant accumulated the highest content of lead in its tissues. The first two genes, are apparently implicated in detoxification and lead accumulation mechanisms, while the other two genes are apparently involved in maintaining cell balance (homeostatic control) and membrane integrity. Our results confirmed that S. minima is efficient for phytoremediation of water bodies contaminated by lead, as it is efficient in accumulating this metal in its tissues (bioconcentration factor; BCF) values greater than 1000, in short times of exposure. More importantly, our data on the expression profiles of four genes coding for transporters, represent a first sight scenario of the molecular basis for understanding the different mechanism of detoxification, apparently present in this aquatic fern.

Identification of up-regulated genes from the metal-hyperaccumulator aquatic fern Salvinia minima Baker, in response to lead exposure.

Lead (Pb) is one of the most serious environmental pollutants. The aquatic fern Salvinia minima Baker is capable to hyper-accumulate Pb in their tissues. However, the molecular mechanisms involved in its Pb accumulation and tolerance capacity are not fully understood. In order to investigate the molecular mechanisms that are activated by S. minima in response to Pb, we constructed a suppression subtractive hybridization library (SSH) in response to an exposure to 40µM of Pb(NO3)2 for 12h. 365 lead-related differentially expressed sequences tags (ESTs) were isolated and sequenced. Among these ESTs, 143 unique cDNA (97 were registered at the GenBank and 46 ESTs were not registered, because they did not meet the GenBank conditions). Those ESTs were identified and classified into 3 groups according to Blast2GO. In terms of metabolic pathways, they were grouped into 29 KEGG pathways. Among the ESTs, we identified some that might be part of the mechanism that this fern may have to deal with this metal, including abiotic-stress-related transcription factors, some that might be involved in tolerance mechanisms such as ROS scavenging, membrane protection, and those of cell homeostasis recovery. To validate the SSH library, 4 genes were randomly selected from the library and analyzed by qRT-PCR. These 4 genes were transcriptionally up-regulated in response to lead in at least one of the two tested tissues (roots and leaves). The present library is one of the few genomics approaches to study the response to metal stress in an aquatic fern, representing novel molecular information and tools to understand the molecular physiology of its Pb tolerance and hyperaccumulation capacity. Further research is required to elucidate the functions of the lead-induced genes that remain classified as unknown, to perhaps reveal novel molecular mechanisms of Pb tolerance and accumulation capacity in aquatic plants.