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Fusarium circinatum poses a threat to both commercial and natural pine forests. Large variation in host resistance exists between species, with many economically important species being susceptible. Development of resistant genotypes could be expedited and optimised by investigating the molecular mechanisms underlying host resistance and susceptibility as well as increasing the available genetic resources. RNA‐seq data, from F. circinatum inoculated and mock‐inoculated ca. 6‐month‐old shoot tissue at 3‐ and 7‐days postinoculation, was generated for three commercially important tropical pines, Pinus oocarpa, Pinus maximinoi and Pinus greggii. De novo transcriptomes were assembled and used to investigate the NLR and PR gene content within available pine references. Host responses to F. circinatum challenge were investigated in P. oocarpa (resistant) and P. greggii (susceptible), in comparison to previously generated expression profiles from Pinus tecunumanii (resistant) and Pinus patula (susceptible). Expression results indicated crosstalk between induced salicylate, jasmonate and ethylene signalling is involved in host resistance and compromised in susceptible hosts. Additionally, higher constitutive expression of sulfur metabolism and flavonoid biosynthesis in resistant hosts suggest involvement of these metabolites in resistance. Summary statement: F. circinatum resistant pines showed higher constitutive sulfur and flavonoid metabolism gene expression and susceptible hosts showed compromised induced responses. Counteracting these compromised pathways through hormone treatment or nutrient supplementation could improve pine resistance. [ABSTRACT FROM AUTHOR]

Climate change challenges the adaptive capacity of several forest tree species in the face of increasing drought and rising temperatures. Therefore, understanding the mechanistic connections between genetic diversity and drought resilience is highly valuable for conserving drought-sensitive forests. Nonetheless, the post-drought recovery in trees from a transcriptomic perspective has not yet been studied by comparing contrasting phenotypes. Here, experimental drought treatments, gas-exchange dynamics and transcriptomic analysis (RNA-seq) were performed in the relict and drought-sensitive fir Abies pinsapo Boiss. to identify gene expression differences over immediate (24 h) and extended drought (20 days). Post-drought responses were investigated to define resilient and sensitive phenotypes. Single nucleotide polymorphisms (SNPs) were also studied to characterize the genomic basis of A. pinsapo drought resilience. Weighted gene co-expression network analysis showed an activation of stomatal closing and an inhibition of plant growth-related genes during the immediate drought, consistent with an isohydric dynamic. During the extended drought, transcription factors, as well as cellular damage and homeostasis protection-related genes prevailed. Resilient individuals activate photosynthesis-related genes and inhibit aerial growth-related genes, suggesting a shifting shoot/root biomass allocation to improve water uptake and whole-plant carbon balance. About, 152 fixed SNPs were found between resilient and sensitive seedlings, which were mostly located in RNA-activity-related genes, including epigenetic regulation. Contrasting gene expression and SNPs were found between different post-drought resilience phenotypes for the first time in a forest tree, suggesting a transcriptomic and genomic basis for drought resilience. The obtained drought-related transcriptomic profile and drought-resilience candidate genes may guide conservation programs for this threatened tree species. [ABSTRACT FROM AUTHOR]

Background De novo phased (haplo)genome assembly using long-read DNA sequencing data has improved the detection and characterization of structural variants (SVs) in plant and animal genomes. Able to span across haplotypes, long reads allow phased, haplogenome assembly in highly outbred organisms such as forest trees. Eucalyptus tree species and interspecific hybrids are the most widely planted hardwood trees with F1 hybrids of Eucalyptus grandis and E. urophylla forming the bulk of fast-growing pulpwood plantations in subtropical regions. The extent of structural variation and its effect on interspecific hybridization is unknown in these trees. As a first step towards elucidating the extent of structural variation between the genomes of E. grandis and E. urophylla , we sequenced and assembled the haplogenomes contained in an F1 hybrid of the two species. Findings Using Nanopore sequencing and a trio-binning approach, we assembled the separate haplogenomes (566.7 Mb and 544.5 Mb) to 98.0% BUSCO completion. High-density SNP genetic linkage maps of both parents allowed scaffolding of 88.0% of the haplogenome contigs into 11 pseudo-chromosomes (scaffold N50 of 43.8 Mb and 42.5 Mb for the E. grandis and E. urophylla haplogenomes, respectively). We identify 48,729 SVs between the two haplogenomes providing the first detailed insight into genome structural rearrangement in these species. The two haplogenomes have similar gene content, 35,572 and 33,915 functionally annotated genes, of which 34.7% are contained in genome rearrangements. Conclusions Knowledge of SV and haplotype diversity in the two species will form the basis for understanding the genetic basis of hybrid superiority in these trees. [ABSTRACT FROM AUTHOR]

We performed gene and genome targeted SNP discovery towards the development of a genome‐wide, multispecies genotyping array for tropical pines. Pooled RNA‐seq data from shoots of seedlings from five tropical pine species was used to identify transcript‐based SNPs resulting in 1.3 million candidate Affymetrix SNP probe sets. In addition, we used a custom 40 K probe set to perform capture‐seq in pooled DNA from 81 provenances representing the natural ranges of six tropical pine species in Mexico and Central America resulting in 563 K candidate SNP probe sets. Altogether, 300 K RNA‐seq (72%) and 120 K capture‐seq (28%) derived SNP probe sets were tiled on a 420 K screening array that was used to genotype 576 trees representing the 81 provenances and commercial breeding material. Based on the screening array results, 50 K SNPs were selected for commercial SNP array production including 20 K polymorphic SNPs for P. patula, P. tecunumanii, P. oocarpa and P. caribaea, 15 K for P. greggii and P. maximinoi, 13 K for P. elliottii and 8K for P. pseudostrobus. We included 9.7 K ancestry informative SNPs that will be valuable for species and hybrid discrimination. Of the 50 K SNP markers, 25% are polymorphic in only one species, while 75% are shared by two or more species. The Pitro50K SNP chip will be useful for population genomics and molecular breeding in this group of pine species that, together with their hybrids, represent the majority of fast‐growing tropical and subtropical pine plantations globally. [ABSTRACT FROM AUTHOR]