Project description:Shrub willow (Salix spp.), a short rotation woody biomass crop, has superior properties as a perennial energy crop for the Northeast and Midwest US. However, the insect pest potato leafhopper Empoasca fabae (Harris) (PLH) can cause serious damage and reduce yield of susceptible genotypes. Currently, the willow cultivars in use display varying levels of susceptibility under PLH infestation. However, genes and markers for resistance to PLH are not yet available for marker-assisted selection in breeding. In this study, transcriptome differences between a resistant genotype 94006 (S. purpurea) and a susceptible cultivar ‘Jorr’ (S. viminalis), and their hybrid progeny were determined. Over 600 million RNA-Seq reads were generated and mapped to the Salix purpurea reference transcriptome. Gene expression analyses revealed the unique defense mechanism in resistant genotype 94006 that involves PLH-induced secondary cell wall modification. In the susceptible genotypes, genes involved in programed cell death were highly expressed, explaining the necrosis symptoms after potato leafhopper feeding. Overall, the discovery of resistance genes and defense mechanisms provides new resources for shrub willow breeding and research in the future.
Project description:Most eukaryotes reproduce sexually and a wealth of different sex determination mechanisms have evolved in this lineage. Dioecy or separate sexes are rare among flowering plants but have repeatedly evolved from hermaphroditic ancestors possibly involving male or female sterility mutations. Willows (Salix spp.) and poplars (Populus spp.) are predominantly dioecious and are members of the Salicaceae family. All studied poplars have sex determination loci on chromosome XIX, however, the position differs among species and both male and female heterogametic system exists. In contrast to the situation in poplars, knowledge of sex determination mechanisms in willows is sparse. In the present study, we have for the first time positioned the sex determination locus on chromosome XV in S. viminalis using quantitative trait locus mapping. All female offspring carried a maternally inherited haplotype, suggesting a system of female heterogamety or ZW. We used a comparative mapping approach and compared the positions of the markers between the S. viminalis linkage map and the physical maps of S. purpurea, S. suchowensis and P. trichocarpa. As we found no evidence for chromosomal rearrangements between chromosome XV and XIX between S. viminalis and P. trichocarpa, it shows that the sex determination loci in the willow and the poplar most likely do not share a common origin and has thus evolved separately. This demonstrates that sex determination mechanisms in the Salicaceae family have a high turnover rate and as such it is excellent for studies of evolutionary processes involved in sex chromosome turnover.
Project description:Salt responsive genes were identified in chinese willow (Salix matsudana) after the plants were treated with 100 mM NaCl. for 48 hours We used microarrays to identify genes responsible for combating salt stress. Those up-regulated during the NaCl treatment may protect the plants from damages caused by salt stress.
Project description:BackgroundSex chromosomes have evolved independently multiple times in eukaryotes and are therefore considered a prime example of convergent genome evolution. Sex chromosomes are known to emerge after recombination is halted between a homologous pair of chromosomes, and this leads to a range of non-adaptive modifications causing gradual degeneration and gene loss on the sex-limited chromosome. However, the proximal causes of recombination suppression and the pace at which degeneration subsequently occurs remain unclear.ResultsHere, we use long- and short-read single-molecule sequencing approaches to assemble and annotate a draft genome of the basket willow, Salix viminalis, a species with a female heterogametic system at the earliest stages of sex chromosome emergence. Our single-molecule approach allowed us to phase the emerging Z and W haplotypes in a female, and we detected very low levels of Z/W single-nucleotide divergence in the non-recombining region. Linked-read sequencing of the same female and an additional male (ZZ) revealed the presence of two evolutionary strata supported by both divergence between the Z and W haplotypes and by haplotype phylogenetic trees. Gene order is still largely conserved between the Z and W homologs, although the W-linked region contains genes involved in cytokinin signaling regulation that are not syntenic with the Z homolog. Furthermore, we find no support across multiple lines of evidence for inversions, which have long been assumed to halt recombination between the sex chromosomes.ConclusionsOur data suggest that selection against recombination is a more gradual process at the earliest stages of sex chromosome formation than would be expected from an inversion and may result instead from the accumulation of transposable elements. Our results present a cohesive understanding of the earliest genomic consequences of recombination suppression as well as valuable insights into the initial stages of sex chromosome formation and regulation of sex differentiation.
Project description:Frost is a major abiotic stress limiting plant growth and development. Climate change models predict an increase in the magnitude and frequency of late-frost events, which, together with an observed loss of soil insulation, will significantly damage roots. To withstand freezing stress, plants have evolved an adaptative process known as cold acclimation. While this process is well documented, it is known that the plant response to multiple stresses is unique and cannot be deduced from the response to each stress taken separately. Here, we investigate the impact of long-term metal exposure on the cold acclimation of Salix viminalis roots. To do so, we used physiological, transcriptomic and proteomic approaches. We found that while metal exposure significantly affected plants morphology and physiology, it did not impede cold acclimation. The impact of the simultaneous exposure to metals and cold acclimation on the transcriptome was unique, while at the proteomic level, the cold acclimation component seemed to be dominant. Further analysis revealed that metals strongly and negatively impacted the cellular antioxidant system. While this should have led to a loss of frost tolerance, it was not observed. A group of proteins was identified that could have played a role in compensating the impediment of the antioxidative system in metal-exposed roots.