A new pear scab resistance gene Rvp1 from the European pear cultivar ‘Navara’ maps in a genomic region syntenic to an apple scab resistance gene cluster on linkage group 2

Scab, caused by the ascomycete fungus Venturia pirina, leads to severe damage on European pear varieties resulting in a loss of commercial value and requiring frequent use of fungicides. Identifying scab resistance genes, developing molecular markers linked to these genes and establishing marker-assisted selection would be an effective way to improve European pear breeding for scab resistance. Most of the European pear cultivars (Pyrus communis) are currently reported to be sensitive. The pear cultivar ‘Navara’ was shown to carry a major scab resistance gene whose phenotypic expression in seedling progenies was a typical stellate necrosis symptom. The resistance gene was called Rvp1, for resistance to V. pirina, and was mapped on linkage group 2 of the pear genome close to microsatellite marker CH02b10. This genomic region is known to carry a cluster of scab resistance genes in apple indicating a first functional synteny for scab resistance between apple and pear

Dissecting the Photoprotective Mechanism Encoded by the flv4-2 Operon: a Distinct Contribution of Sll0218 in Photosystem II Stabilization

In Synechocystis sp. PCC 6803, the flv4-2 operon encodes the flavodiiron proteins Flv2 and Flv4 together with a small protein, Sll0218, providing photoprotection for Photosystem II (PSII). Here, the distinct roles of Flv2/Flv4 and Sll0218 were addressed, using a number of flv4-2 operon mutants. In the sll0218 mutant, the presence of Flv2/Flv4 rescued PSII functionality as compared with sll0218-flv2, where neither Sll0218 nor the Flv2/Flv4 heterodimer are expressed. Nevertheless, both the sll0218 and sll0218-flv2 mutants demonstrated deficiency in accumulation of PSII proteins suggesting a role for Sll0218 in PSII stabilization, which was further supported by photoinhibition experiments. Moreover, the accumulation of PSII assembly intermediates occurred in Sll0218-lacking mutants. The YFP-tagged Sll0218 protein localized in a few spots per cell at the external side of the thylakoid membrane, and biochemical membrane fractionation revealed clear enrichment of Sll0218 in the PratA-defined membranes, where the early biogenesis steps of PSII occur. Further, the characteristic antenna uncoupling feature of the flv4-2 operon mutants is shown to be related to PSII destabilization in the absence of Sll0218. It is concluded that the Flv2/Flv4 heterodimer supports PSII functionality, while the Sll0218 protein assists PSII assembly and stabilization, including optimization of light harvesting. This work clarifies and dissects the roles of the flv4-2 operon-encoded proteins, Flv2/Flv4 heterodimer and the elusive Sll0218, in photoprotection of the photosynthetic apparatus in Synechosystis. While Flv2/Flv4 heterodimer is involved in an alternative electron transfer route, the Sll0218 protein is localized to specific cell compartments where photosynthetic complexes are assembled, and it is involved in the stabilization of Photosystem II complexes

High-quality de novo assembly of the apple genome and methylome dynamics of early fruit development

Using the latest sequencing and optical mapping technologies, we have produced a high-quality de novo assembly of the apple (Malus domestica Borkh.) genome. Repeat sequences, which represented over half of the assembly, provided an unprecedented opportunity to investigate the uncharacterized regions of a tree genome; we identified a new hyper-repetitive retrotransposon sequence that was over-represented in heterochromatic regions and estimated that a major burst of different transposable elements (TEs) occurred 21 million years ago. Notably, the timing of this TE burst coincided with the uplift of the Tian Shan mountains, which is thought to be the center of the location where the apple originated, suggesting that TEs and associated processes may have contributed to the diversification of the apple ancestor and possibly to its divergence from pear. Finally, genome-wide DNA methylation data suggest that epigenetic marks may contribute to agronomically relevant aspects, such as apple fruit development

Redefinition of the map position and validation of a major quantitative trait locus for fire blight resistance of the pear cultivar ‘Harrow Sweet’ (Pyrus communis L.)

In a previous study, a QTL analysis was conducted on a pear F1 progeny derived from a cross ‘Passe Crassane’ (PC) × ‘Harrow Sweet’ (HS). Four genomic regions associated with fire blight resistance were identified, including two main QTL located on linkage groups (LGs), 2A and 4 of ‘Harrow Sweet’ (HS02A and HS04). In the present study, we report the combination of LGs HS02A and HS02B into a single LG by mapping additional SSR loci from Malus or Pyrus spp. We could thereby precisely identify a single major QTL on LG HS02. We also confirm a putative QTL on LG HS04 by including new SSR markers to the pre-existing LG HS04. Based on SSR marker analysis of ‘Harrow Sweet’ pedigree, the major HS02 QTL is presumed to originate from the cultivar ‘Early Sweet’, while the HS04 QTL was traced from ‘Harrow Sweet’ back to ‘Bartlett’. We also describe the validation of the major HS02 QTL for the fire blight severity trait in a second F1 progeny derived from a cross ‘Angelys’ × ‘Harrow Sweet’

An overview of the position and robustness of scab resistance QTLs and major genes by aligning of genetic maps in five apple progenies

In the frame of the D.A.R.E. project, five mapping populations have been studied for partial scab resistance against several races of Venturia inaequalis. A main objective was to identify QTLs (quantitative traits loci) with broad spectrum of resistance towards a wide range of strains of the fungus. Genetic markers (mainly SSR and AFLP) were tested on each population and genetic maps were constructed for both parents of each population. Meanwhile, pathological tests with several isolates of different races of V. inaequalis were performed. Four major genomic regions appear to be involved in scab resistance: they are located on linkage groups (LG) LG-1, LG-2, LG-11, and LG-17. Some other linkage groups carry either QTLs or major resistance genes that are isolate specific: a QTL on LG-5, Vd on LG-10, and Vg on LG-12. The QTL region located on LG-17 clearly exhibited the widest spectrum of resistanc

Klärung der Elternschaft der Apfelsorte ‘Meran’

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