Structural and molecular analysis of self-incompatibility in almond ( Prunus dulcis )

Abstract

A multi-approach was used to study different aspects of self-incompatibility (SI) in almond (Prunus dulcis). First, a population of almond cultivars was characterised as to their individual S-allele combination using separation of stylar protein extracts (non-equilibrium pH gradient electrofocusing) followed by staining for RNase activity, which led to the identification of one putative new allele and several new S-allele combinations. Second, a field pollination scheme was designed to study pollen tube progression and to obtain a spatial and temporal characterisation of this reproductive stage in both incompatible and compatible crosses. In addition, an antiserum was raised against a synthetic peptide designed from an almond S-protein (S 8 ) and used for immunological in situ detection in pistil cryosections. S-RNases were found to accumulate intercellularly in the stylar transmitting tissue as previously reported for other rosaceous species. The results are discussed in view of the evolution of the gametophytic SI system and the models proposed for its mechanism. Gametophyte selection is also proposed as an important intraspecific barrier to fertilisation in this species.

Genetic relatedness of Portuguese almond cultivars assessed by RAPD and ISSR markers

“…'Boa Casta' from Algarve and from Trµs-os-Montes have a similarity coefficient of 0.94 thus representing the same cultivar [they also have the same Sallele composition, S8S21 (Ma and Oliveira 2001;Certal et al 2002)]. The two accessions of 'Bonita de S¼o Braz' were considered to be homonyms (different genotype under the same name) since their similarity is only 0.81.…”

Phylogenetic relationships among the first and second introns of selectedPrunus S-RNase genes

“…Interspecies hybridization and subsequent introgression appear relatively common within this subgenus as documented by the introgression of selfcompatibility to cultivated almond from P. webbii (Spach) Vieh. (Godini 2000;Certal et al 2002;Martı´nez-Go´mez et al 2007). The Prunus self-incompatibility system differs from other widely studied self-incompatibility systems, such as in the Solanaceae, by the absence of strong breeding barriers to interspecific hybridization/introgression (Gradziel 2011).…”

“…Although most samples were of a species other than P. dulcis, naming was done based on the alleles to which they had maximum homology in GenBank since interspecies exchange has been documented in this subgenus (Godini 2000;Certal et al 2002;Martı´nez-Go´mez et al 2007). Sequences in the first intron showed a maximum identity from 84% in band 418 bp for sample #116 (P. carduchorum) with S4 RNase of P. webbii in NCBI, to 99% in band 348 bp for sample #100 (P. spartioides) with S29 precuror gene of P. dulcis, and 99% in band 336 bp for sample #116 (P. carduchorum) with S1/S3 of P. dulcis.…”

“…Alleles conferring self-compatibility have been identified (Lo´pez et al 2006), usually being derived from wild species (Certal et al 2002), though their mode of action is not fully understood Banovic et al 2009). When the S-allele haplotype of the pollen is identical to either of the two S-alleles present in diploid pistil, pollen tube growth will be arrested (Pimienta et al 1983;Channuntapipat et al 2001;Kodad et al 2008b) and fertilization prevented.…”

Trans-specific S-RNase and SFB alleles in Prunus self-incompatibility haplotypes

“…Prunus cerasifera accession M3 gave two S-RNase sequences, S 3 and S 6 , and the deduced polypeptide of one of them held 97.6% identity with a putative polypeptide of S 12 Table 1 Description of six trans-speciWc S-haplotypes sequenced from P. cerasifera and P. domestica and their transspeciWc pair alleles in other species of Prunus (Certal et al 2002), with three non-conserved and one conserved amino acid diVerences occurring out of 169 residues in the available deduced polypeptide chain (Fig. 1a).…”