Comparison of conventional and temporary immersion systems on micropropagation (multiplication phase) of Agave angustifolia Haw. 'Bacanora'.

The aim of this study was to improve the quality of the micropropagated A. angustifolia Haw. plants cultured in temporary immersion bioreactors (TIS) comparing them with those produced through conventional semisolid-solid tissue culture system (SS). The Recipient for Automated Temporary Immersion (RITA®) bioreactor was used as TIS in this work. The effect of different culture conditions, such as explants density, genotype, and duration of the incubation stages, were analyzed. The growth and morphological parameters measured for the in vitro cultured plants were: plant height, number of new leaves, number of shoots/explants, growth index (GI), dry mass content, and water content. In all experiments, it was observed that plantlets cultivated in the TIS grew larger than those cultivated in SS. Analyzing all the parameters used in this study, the results showed that RITA bioreactor generates a better shoot production and a better GI when using 20 plantlets per container. The number of shoots increased with time of culture (60 days) in both systems. However, the shoots and plantlets cultivated in TIS grew bigger and showed better quality (did not present necrosis in the leaves) than the ones cultured in SS. This study provides experimental evidence that the application of TIS for micropropagation of A. angustifolia is a viable option for the production of high-quality shoots for reforestation purposes.

Transcriptomics and co-expression networks reveal tissue-specific responses and regulatory hubs under mild and severe drought in papaya (Carica papaya L.).

Plants respond to drought stress through the ABA dependent and independent pathways, which in turn modulate transcriptional regulatory hubs. Here, we employed Illumina RNA-Seq to analyze a total of 18 cDNA libraries from leaves, sap, and roots of papaya plants under drought stress. Reference and de novo transcriptomic analyses identified 8,549 and 6,089 drought-responsive genes and unigenes, respectively. Core sets of 6 and 34 genes were simultaneously up- or down-regulated, respectively, in all stressed samples. Moreover, GO enrichment analysis revealed that under moderate drought stress, processes related to cell cycle and DNA repair were up-regulated in leaves and sap; while responses to abiotic stress, hormone signaling, sucrose metabolism, and suberin biosynthesis were up-regulated in roots. Under severe drought stress, biological processes related to abiotic stress, hormone signaling, and oxidation-reduction were up-regulated in all tissues. Moreover, similar biological processes were commonly down-regulated in all stressed samples. Furthermore, co-expression network analysis revealed three and eight transcriptionally regulated modules in leaves and roots, respectively. Seventeen stress-related TFs were identified, potentially serving as main regulatory hubs in leaves and roots. Our findings provide insight into the molecular responses of papaya plant to drought, which could contribute to the improvement of this important tropical crop.

Fungal Screening on Olive Oil for Extracellular Triacylglycerol Lipases: Selection of a Trichoderma harzianum Strain and Genome Wide Search for the Genes.

A lipolytic screening with fungal strains isolated from lignocellulosic waste collected in banana plantation dumps was carried out. A Trichoderma harzianum strain (B13-1) showed good extracellular lipolytic activity (205 UmL-1). Subsequently, functional screening of the lipolytic activity on Rhodamine B enriched with olive oil as the only carbon source was performed. The successful growth of the strain allows us to suggest that a true lipase is responsible for the lipolytic activity in the B13-1 strain. In order to identify the gene(s) encoding the protein responsible for the lipolytic activity, in silico identification and characterization of triacylglycerol lipases from T. harzianum is reported for the first time. A survey in the genome of this fungus retrieved 50 lipases; however, bioinformatic analyses and putative functional descriptions in different databases allowed us to choose seven lipases as candidates. Suitability of the bioinformatic screening to select the candidates was confirmed by reverse transcription polymerase chain reaction (RT-PCR). The gene codifying 526309 was expressed when the fungus grew in a medium with olive oil as carbon source. This protein shares homology with commercial lipases, making it a candidate for further applications. The success in identifying a lipase gene inducible with olive oil and the suitability of the functional screening and bioinformatic survey carried out herein, support the premise that the strategy can be used in other microorganisms with sequenced genomes to search for true lipases, or other enzymes belonging to large protein families.

Transcriptional profiling of sugarcane leaves and roots under progressive osmotic stress reveals a regulated coordination of gene expression in a spatiotemporal manner.

Sugarcane is one of the most important crops worldwide and is a key plant for the global production of sucrose. Sugarcane cultivation is severely affected by drought stress and it is considered as the major limiting factor for their productivity. In recent years, this plant has been subjected to intensive research focused on improving its resilience against water scarcity; particularly the molecular mechanisms in response to drought stress have become an underlying issue for its improvement. To better understand water stress and the molecular mechanisms we performed a de novo transcriptomic assembly of sugarcane (var. Mex 69-290). A total of 16 libraries were sequenced in a 2x100 bp configuration on a HiSeq-Illumina platform. A total of 536 and 750 genes were differentially up-regulated along with the stress treatments for leave and root tissues respectively, while 1093 and 531 genes were differentially down-regulated in leaves and roots respectively. Gene Ontology functional analysis showed that genes related to response of water deprivation, heat, abscisic acid, and flavonoid biosynthesis were enriched during stress treatment in our study. The reliability of the observed expression patterns was confirmed by RT-qPCR. Additionally, several physiological parameters of sugarcane were significantly affected due to stress imposition. The results of this study may help identify useful target genes and provide tissue-specific data set of genes that are differentially expressed in response to osmotic stress, as well as a complete analysis of the main groups is significantly enriched under this condition. This study provides a useful benchmark for improving drought tolerance in sugarcane and other economically important grass species.

RAP2.4a Is Transported through the Phloem to Regulate Cold and Heat Tolerance in Papaya Tree (Carica papaya cv. Maradol): Implications for Protection Against Abiotic Stress.

Plants respond to stress through metabolic and morphological changes that increase their ability to survive and grow. To this end, several transcription factor families are responsible for transmitting the signals that are required for these changes. Here, we studied the transcription factor superfamily AP2/ERF, particularly, RAP2.4 from Carica papaya cv. Maradol. We isolated four genes (CpRap2.4a, CpRAap2.4b, CpRap2.1 and CpRap2.10), and an in silico analysis showed that the four genes encode proteins that contain a conserved APETALA2 (AP2) domain located within group I and II transcription factors of the AP2/ERF superfamily. Semiquantitative PCR experiments indicated that each CpRap2 gene is differentially expressed under stress conditions, such as extreme temperatures. Moreover, genetic transformants of tobacco plants overexpressing CpRap2.4a and CpRap2.4b genes show a high level of tolerance to cold and heat stress compared to non-transformed plants. Confocal microscopy analysis of tobacco transgenic plants showed that CpRAP2.4a and CpRAP2.4b proteins were mainly localized to the nuclei of cells from the leaves and roots and also in the sieve elements. Moreover, the movement of CpRap2.4a RNA in tobacco grafting was analyzed. Our results indicate that CpRap2.4a and CpRap2.4b RNA in the papaya tree have a functional role in the response to stress conditions such as exposure to extreme temperatures via direct translation outside the parental RNA cell.

Comparative Genomics of NAC Transcriptional Factors in Angiosperms: Implications for the Adaptation and Diversification of Flowering Plants.

NAC proteins constitute one of the largest groups of plant-specific transcription factors and are known to play essential roles in various developmental processes. They are also important in plant responses to stresses such as drought, soil salinity, cold, and heat, which adversely affect growth. The current knowledge regarding the distribution of NAC proteins in plant lineages comes from relatively small samplings from the available data. In the present study, we broadened the number of plant species containing the NAC family origin and evolution to shed new light on the evolutionary history of this family in angiosperms. A comparative genome analysis was performed on 24 land plant species, and NAC ortholog groups were identified by means of bidirectional BLAST hits. Large NAC gene families are found in those species that have experienced more whole-genome duplication events, pointing to an expansion of the NAC family with divergent functions in flowering plants. A total of 3,187 NAC transcription factors that clustered into six major groups were used in the phylogenetic analysis. Many orthologous groups were found in the monocot and eudicot lineages, but only five orthologous groups were found between P. patens and each representative taxa of flowering plants. These groups were called basal orthologous groups and likely expanded into more recent taxa to cope with their environmental needs. This analysis on the angiosperm NAC family represents an effort to grasp the evolutionary and functional diversity within this gene family while providing a basis for further functional research on vascular plant gene families.