Applying Synteny Networks (SynNet) to Study Genomic Arrangements of Protein-Coding Genes in Plants.

In comparative genomics, the study of synteny can be a powerful method for exploring genome rearrangements, inferring genomic ancestry, defining orthology relationships, determining gene and genome duplications, and inferring gene positional conservation patterns across taxa. In this chapter, we present a step-by-step protocol for microsynteny network (SynNet) analysis, as an alternative to traditional methods of synteny comparison, where nodes in the network represent protein-coding genes and edges represent the pairwise syntenic relationships. The SynNet pipeline consists of six main steps: (1) pairwise genome comparisons between all the genomes being analyzed, (2) detection of inter- and intrasynteny blocks, (3) generation of an entire synteny database (i.e., edgelist), (4) network clustering, (5) phylogenomic profiling of the gene family of interest, and (6) evolutionary inference. The SynNet approach facilitates the rapid analysis and visualization of synteny relationships (from specific genes, specific gene families up to all genes) across a large number of genomes.

Phylogenomic and Microsynteny Analysis Provides Evidence of Genome Arrangements of High-Affinity Nitrate Transporter Gene Families of Plants.

Nitrate transporter 2 (NRT2) and NRT3 or nitrate-assimilation-related 2 (NAR2) proteins families form a two-component, high-affinity nitrate transport system, which is essential for the acquisition of nitrate from soils with low N availability. An extensive phylogenomic analysis across land plants for these families has not been performed. In this study, we performed a microsynteny and orthology analysis on the NRT2 and NRT3 genes families across 132 plants (Sensu lato) to decipher their evolutionary history. We identified significant differences in the number of sequences per taxonomic group and different genomic contexts within the NRT2 family that might have contributed to N acquisition by the plants. We hypothesized that the greater losses of NRT2 sequences correlate with specialized ecological adaptations, such as aquatic, epiphytic, and carnivory lifestyles. We also detected expansion on the NRT2 family in specific lineages that could be a source of key innovations for colonizing contrasting niches in N availability. Microsyntenic analysis on NRT3 family showed a deep conservation on land plants, suggesting a high evolutionary constraint to preserve their function. Our study provides novel information that could be used as guide for functional characterization of these gene families across plant lineages.

The SoNAP gene from sugarcane (Saccharum officinarum) encodes a senescence-associated NAC transcription factor involved in response to osmotic and salt stress.

Climate change has caused serious problems related to the productivity of agricultural crops directly affecting human well-being. Plants have evolved to produce molecular mechanisms in response to environmental stresses, such as transcription factors (TFs), to cope with abiotic stress. The NAC proteins constitute a plant-specific family of TFs involved in plant development processes and tolerance to biotic and abiotic stress. Sugarcane is a perennial grass that accumulates a large amount of sucrose and is a crucial agro-industry crop in tropical regions. Our previous transcriptome analyses on sugarcane that were exposed to drought conditions revealed significant increases in the expression of several NAC TFs through all of the time-point stress conditions. In this work, we characterize all previously detected sugarcane NAC genes, utilizing phylogenetics and expression analyses. Furthermore, we characterized a sugarcane NAC gene orthologous to the senescence-associated genes AtNAP and OsNAP via transient expression in tobacco calluses, from Arabidopsis and rice respectively, thus we named it the SoNAP gene. Transient localization assays on onion epidermal cells confirmed the nuclear localization of the SoNAP. Expression analysis showed that the SoNAP gene was induced by high salinity, drought, and abscisic acid treatments. The overexpression of the SoNAP gene in tobacco calluses caused a senescence associated phenotype. Overall, our results indicated that the SoNAP gene from sugarcane is transcriptionally induced under abiotic stress conditions and conserved the predicted senescence-associated functions when it was overexpressed in a heterologous plant model. This work provides key insights about the senescence mechanisms related to abiotic stress and it provides a benchmark for future work on the improvement of this economically important crop.

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.