Legumes form endosymbiotic interaction with host compatible rhizobia, resulting in the development of nitrogen-fixing root nodules. Within symbiotic nodules, rhizobia are intracellularly accommodated in plant-derived membrane compartments, termed symbiosomes. In mature nodule, the massively colonized cells tolerate the existence of rhizobia without manifestation of visible defense responses, indicating the suppression of plant immunity in the nodule in the favur of the symbiotic partner. Medicago truncatula DNF2 (defective in nitrogen fixation 2) and NAD1 (nodules with activated defense 1) genes are essential for the control of plant defense during the colonization of the nitrogen-fixing nodule and are required for bacteroid persistence. The previously identified nodule-specific NAD1 gene encodes a protein of unknown function. Herein, we present the analysis of novel NAD1 mutant alleles to better understand the function of NAD1 in the repression of immune responses in symbiotic nodules. By exploiting the advantage of plant double and rhizobial mutants defective in establishing nitrogen-fixing symbiotic interaction, we show that NAD1 functions following the release of rhizobia from the infection threads and colonization of nodule cells. The suppression of plant defense is self-dependent of the differentiation status of the rhizobia. The corresponding phenotype of nad1 and dnf2 mutants and the similarity in the induction of defense-associated genes in both mutants suggest that NAD1 and DNF2 operate close together in the same pathway controlling defense responses in symbiotic nodules.

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The hexaploid European plum (Prunus domestica L.) is an economically important fruit species with limited information on its genetic structure. Our objective was to fingerprint 55 cultivars using seven simple sequence repeat (SSR) markers to estimate the polymorphism level and determine allelic variation and genetic relationships among local and international cultivars. The primer pairs amplified a total of 135 alleles ranging from six to 27 alleles per locus, displaying high polymorphism. All genotypes were clearly distinguished with the seven SSRs used in this study. In a neighbor-joining cluster analysis, cultivars belonging to the same species did not group together. Foreign modern cultivars clustered together, and Hungarian landraces positioned distantly from those. STRUCTURE analysis indicated three genetically distinct groups of the studied genotypes. Each cluster of Hungarian landrace cultivars received strong bootstrap support (89% to 100%). Most genotypes kept under identical name showed different DNA fingerprints. A principal component analysis (PCA) confirmed the information provided by the dendrogram and clarified the origin of ʻFehérszilva’. Our results confirmed the potential of the application of SSR markers in plum breeding.

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Apple exhibits self-incompatibility controlled by the multiallelic S-locus. Twenty-three old apple cultivars were S-genotyped using three different approaches (allele-specific polymerase chain reaction (PCR) + cleaved amplified polymorphic sequences (CAPS), consensus PCR + sequencing and consensus PCR+CAPS) to compare the robustness and reliability of these techniques and characterise genotypes from the Carpathian basin that might be useful in resistance breeding. Best results were obtained using the ASPF3 and ASPR3S consensus primer pair that detected 96% of all alleles carried by the 23 cultivars tested. Flow cytometry analysis was also needed to control the completeness of the genotypes as was seen in case of a tetraploid cultivar with only three assigned S-alleles. The genetic disparity between the old Carpathian basin and modern apple cultivars was indicated by differences in allele frequency data (S 9 , S 24 and S 26 ) as well as single nucleotide polymorphisms in S 1 , S 2 , S 7 S 24 and S 26 and indels in S 20 and S 26 alleles. An alignment of partial genomic sequences indicated trans-specific and transgeneric evolution of S-ribonuclease alleles in the Maloideae subfamily (S 26 and S 28 ) and a possibly recent introgression event (S 1 ) between Malus×domestica and Malus sylvestris. These data suggest that the genome of old cultivars from the Carpathian basin was enriched by several Malus taxa and are free from the consequences of modern breeding. These cultivars may contribute to the widening of the genetic basis of cultivated apple and prevent genetic erosion in future commercial cultivars.