Methylation of the S locus in almond is associated with S-RNase loss of function.

Self-compatibility in almond ( Prunus dulcis) is attributed to the presence of the S haplotype, allelic to and dominant over the series of S-alleles controlling self-incompatibility. Some forms of the S haplotype, however, are phenotypically self-incompatible even though their nucleotide sequences are identical. DNA from leaves and styles from genetically diverse almond samples was cloned and sequenced and then analyzed for changes affecting S-RNase variants. Epigenetic changes in several cytosine residues were detected in a fragment of 4,700 bp of the 5′ upstream region of all self-compatible samples of the S-RNases, differentiating them from all self-incompatible samples of S-RNases analyzed. This is the first report of DNA methylation in a Rosaceae species and appears to be strongly associated with inactivation of the S allele. Results facilitate an understanding of the evolution of self-compatibility/self-incompatibility in almond and other Prunus species, and suggest novel approaches for future crop improvement. [ABSTRACT FROM AUTHOR]