EPIGENETIC AND GENETIC VARIATION IN MICRO-PROPAGATED STRAWBERRY PLANTS

Epigenetic and genetic variation often present in micro-propagated strawberry plants. In the past five years, we systematically investigated the phenomena of epigenetic and genetic variation displayed by the micro-propagated strawberry plants and its offsprings. To elucidate the mechanism of epigenetic variation, DNA methylation and microRNAs (miRNAs) were analyzed. Methylation sensitive amplified polymorphism (MSAP) showed that the methylation level was lower in micro-propagated plants than in conventionally propagated runner plants, and in the asexual descendants of the micro-propagated plants it increased gradually in the field. The transcriptional expressions of both methyltransferase (MET1) and domain-rearranged methyltransferase (DRM) genes were downregulated in micro-propagated plants, and they were recovered in the first and second runner generations of micro-propagated plants. To discover the expression difference of miRNAs between conventional and micro-propagated strawberry plants, we carried out the detection and quantification of strawberry miRNAs by microarray and real time PCR. Seventy-four miRNAs were checked in leaves of strawberry and four miRNA genes displayed clear expression difference between conventional and micro-propagated strawberry plants, including two upregulated genes (miR535 and miR390) and two downregulated genes (miR169a and miR169d). The genetic variation was detected with the sequence-specific amplification polymorphism (S-SAP) markers, and a 187 bp different S-SAP band appeared in the strawberry plants regenerated from leaves in vitro. Among the micro-propagated strawberry plants, a stable mutant with white berry was found. The phenotype and physiology were compared between wild type and mutant. To elucidate the mechanism of color formation, the gene expression profiles in berry were analyzed with transcriptome and small RNAs data.