A PARTHENOGENESIS allele from apomictic dandelion can induce egg cell division without fertilization in lettuce

The PARTHENOGENESIS (PAR) gene is identified in apomictic dandelion. A dominant allele has a MITE transposon insertion similar to that found in apomictic hawkweed. Expression of dandelion PAR in lettuce induces embryo-like structures without fertilization. Apomixis, the clonal formation of seeds, is a rare yet widely distributed trait in flowering plants. We have isolated the PARTHENOGENESIS (PAR) gene from apomictic dandelion that triggers embryo development in unfertilized egg cells. PAR encodes a K2-2 zinc finger, EAR-domain protein. Unlike the recessive sexual alleles, the dominant PAR allele is expressed in egg cells and has a miniature inverted-repeat transposable element (MITE) transposon insertion in the promoter. The MITE-containing promoter can invoke a homologous gene from sexual lettuce to complement dandelion LOSS OF PARTHENOGENESIS mutants. A similar MITE is also present in the promoter of the PAR gene in apomictic forms of hawkweed, suggesting a case of parallel evolution. Heterologous expression of dandelion PAR in lettuce egg cells induced haploid embryo-like structures in the absence of fertilization. Sexual PAR alleles are expressed in pollen, suggesting that the gene product releases a block on embryogenesis after fertilization in sexual species while in apomictic species PAR expression triggers embryogenesis in the absence of fertilization.

Automated summary

The PAR gene in dandelion triggers embryo development without fertilization, a rare phenomenon in flowering plants. This gene is inserted with a MITE transposon in the promoter region, and its expression is able to induce embryogenesis in the absence of fertilization.