Gamete expression of TALE class HD genes activates the diploid sporophyte program in < i > Marchantia polymorpha < /i >

Eukaryotic life cycles alternate between haploid and diploid phases and in phylogenetically diverse unicellular eukaryotes, expression of paralogous homeodomain genes in gametes primes the haploid-to-diploid transition. In the unicellular Chlorophyte algaChlamydomonas KNOX and BELL TALE-homeodomain genes mediate this transition. We demonstrate that in the liverwortMarchantia polymorpha paternal (sperm) expression of three of five phylogenetically diverse BELL genes, MpBELL234, and maternal (egg) expression of both MpKNOX1 and MpBELL34mediate the haploid-to-diploid transition. Loss-of-function alleles of MpKNOX1 result in zygotic arrest, whereas loss of either maternal or paternal MpBELL234 results in variable zygotic and early embryonic arrest. Expression of MpKNOX1 and MpBELL34 during diploid sporophyte development is consistent with a later role for these genes in patterning the sporophyte. These results indicate that the ancestral mechanism to activate diploid gene expression was retained in early diverging land plants and subsequently co-opted during evolution of the diploid sporophyte body.
Source: eLife - Category: Biomedical Science Tags: Developmental Biology Evolutionary Biology Source Type: research