Expression of Fragaria vesca PIP aquaporins in response to drought stress: PIP down-regulation correlates with the decline in substrate moisture content

PIP aquaporin responses to drought stress can vary considerably depending on the isoform, tissue, species or level of stress; however, a general down-regulation of these genes is thought to help reduce water loss and prevent backflow of water to the drying soil. It has been suggested therefore, that it may be necessary for the plant to limit aquaporin production during drought stress, but it is unknown whether aquaporin down-regulation is gradual or triggered by a particular intensity of the stress. In this study, ten Fragaria PIP genes were identified from the woodland strawberry (Fragaria vesca L.) genome sequence and characterised at the sequence level. The water relations of F. vesca were investigated and the effect of different intensities of drought stress on the expression of four PIP genes, as well as how drought stress influences their diurnal transcription was determined. PIP down-regulation in the root corresponded to the level of drought stress. Moreover, transcript abundance of two genes highly expressed in the root (FvPIP1;1 and FvPIP2;1) was strongly correlated to the decline in substrate moisture content. The amplitude of diurnal aquaporin expression in the leaves was down-regulated by drought without altering the pattern, but showing an intensity-dependent effect. The results show that transcription of PIP aquaporins can be fine-tuned with the environment in response to declining water availabilit

Mapping QTL associated with Verticillium dahliae resistance in the cultivated strawberry (Fragaria 3 ananassa)

A biparental cross of octoploid strawberry segregating for resistance to Verticillium dahliae, the causative agent of Verticillium wilt, was screened under field conditions for three seasons. Average wilt scores were significantly associated with multiple QTL, which were mostly significant across all years. Markers significantly associated with the traits were used to screen material with known wilt resistance and susceptibility phenotypes. A clear and statistically significant relationship was observed between resistant, tolerant and susceptible material and the total number of markers present in the different resistance classes. In field situations resistance QTL appear to behave in an additive manner. These markers are abundant in the cultivated strawberry germplasm indicating that, despite the large number of markers, clear genetic gain is possible through marker-assisted breeding

Characterisation of the virescent locus controlling a recessive phenotype in apple rootstocks (Malus pumila Mill.)

Certain progenies of Malling apple rootstocks (Malus pumila) have been reported to segregate for a virescent trait: leaves are chlorotic at germination or bud break but turn green as the season progresses. The M432 rootstock mapping progeny, from which a linkage map has recently been elaborated with 323 simple sequence repeat (SSR) markers and 3,069 single nucleotide polymorphism (SNP) markers, also segregates for this phenotype. In this investigation, 188 seedlings were scored and, on the basis of a 3:1 segregation, virescence was attributed to the recessive gene (vir) for which the two parents, M.27 and M.116, are heterozygous. At least seven of 28 Malling rootstocks are heterozygous for this apparently deleterious trait. With the published marker data the gene was mapped to linkage group 12, tightly flanked by the SSR CH01g12 and the SNP marker 475880474, and was located in a physical interval of 2.36 Mb on the Golden Delicious genome sequence. A PCR-based marker was developed from the SNP and along with the SSR was scored in a set of Malus rootstock accessions. The screening of this collection demonstrated that those accessions known to be heterozygous at the vir locus all carried the 152 allele of the SSR and the G allele of the SNP, whilst a virescent accession was homozygous for the alleles. The results we present here could help predict the genotype of apple rootstocks at the vir locus, assist in the fine mapping of the vir locus to identify potential candidate genes for the trait and also aid rootstock breedin

A microsatellite linkage map for the cultivated strawberry (Fragaria 3 ananassa) suggests extensive regions of homozygosity in the genome that may have resulted from breeding and selection

The linkage maps of the cultivated strawberry, Fragaria 9 ananassa (2n = 8x = 56) that have been reported to date have been developed predominantly from AFLPs, along with supplementation with transferrable microsatellite (SSR) markers. For the investigation of the inheritance of morphological characters in the cultivated strawberry and for the development of tools for markerassisted breeding and selection, it is desirable to populate maps of the genome with an abundance of transferrable molecular markers such as microsatellites (SSRs) and gene-specific markers. Exploiting the recent release of the genome sequence of the diploid F. vesca, and the publication of an extensive number of polymorphic SSR markers for the genus Fragaria, we have extended the linkage map of the ‘Redgauntlet’ 9 ‘Hapil’ (RG 9 H) mapping population to include a further 330 loci, generated from 160 primer pairs, to create a linkage map for F. 9 ananassa containing 549 loci, 490 of which are transferrable SSR or gene-specific markers. The map covers 2140.3 cM in the expected 28 linkage groups for an integrated map (where one group is composed of two separate male and female maps), which represents an estimated 91% of the cultivated strawberry genome. Despite the relative saturation of the linkage map on the majority of linkage groups, regions of apparent extensive homozygosity were identified in the genomes of ‘Redgauntlet’ and ‘Hapil’ which may be indicative of allele fixation during the breeding and selection of modern F. 9 ananassa cultivars. The genomes of the octoploid and diploid Fragaria are largely collinear, but through comparison of mapped markers on the RG 9 H linkage map to their positions on the genome sequence of F. vesca, a number of inversions were identified that may have occurred before the polyploidisation event that led to the evolution of the modern octoploid strawberry specie

Functional gametophytic self-incompatibility in a peripheral population of Solanum peruvianum (Solanaceae)

The transition from self-incompatibility to self-compatibility is a common transition in angiosperms often reported in populations at the edge of species range limits. Geographically distinct populations of wild tomato species (Solanum section Lycopersicon (Solanaceae)) have been described as polymorphic for mating system with both self-incompatible and self-compatible populations. Using controlled pollinations and sequencing of the S-RNase mating system gene, we test the compatibility status of a population of S. peruvianum located near its southern range limit. Pollinations among plants of known genotypes revealed strong self-incompatibility; fruit set following compatible pollinations was significantly higher than following incompatible pollinations for all tested individuals. Sequencing of the S-RNase gene in parents and progeny arrays was also as predicted under self-incompatibility. Molecular variation at the S-RNase locus revealed a diverse set of alleles, and heterozygosity in over 500 genotyped individuals. We used controlled crosses to test the specificity of sequences recovered in this study; in all cases, results were consistent with a unique allelic specificity for each tested sequence, including two alleles sharing 92% amino-acid similarity. Site-specific patterns of selection at the S-RNase gene indicate positive selection in regions of the gene associated with allelic specificity determination and purifying selection in previously characterized conserved regions. Further, there is broad convergence between the present and previous studies in specific amino-acid positions inferred to be evolving under positive selection