Genetic evidence for paternal inheritance of the chloroplast in four Australian Callitris species (Cupressaceae)

The mode of chloroplast inheritance was investigated in the four Australian conifer species; Callitris columellaris, C. intratropica, C. gracilis and C. verrucosa (Callitroideae, Cupressaceae), as a basis for future use of chloroplast genetic markers for the genus. Open-pollinated seeds and the foliage tissue of the mother trees were collected from one population per species, in which two distinct chloroplast haplotypes at the trnL (UAA) 5′ exon-trnF (GAA) region were co-distributed. In total, the DNA sequences of the chloroplast fragments in 255 samples were determined, and the haplotypes of the germinated seedlings and the mother trees were compared. Among the 16 mother trees examined across all species, 12 trees were shown to have produced at least one offspring with a different haplotype from the mother, indicating the occurrence of paternal inheritance of chloroplast in the fertilization processes. In binomial GLMM analyses, the haplotype of mother trees in C. columellaris, C. gracilis, and C. verrucosa did not significantly affect those of their offspring, and the predicted frequency of seedlings' haplotypes was compatible with the observed frequency in adult canopy trees. These findings provide a genetic support that paternal inheritance of chloroplast DNA via pollen dispersal would be dominant in the Callitris species.