Assigning functions to the Marchantia polymorpha MpKNX1C gene
Evolution and Systematics of Plants and Fungi
Plant Genetics and Genomics
Final Report Abstract
The advent of terrestrial flora from their Charophycean algal ancestors was one of the most formative events in evolutionary history. This aquatic to terrestrial transition required substantial morphological and physiological adaptations to respond to novel biotic and abiotic stressors. A key invention of land plants that had a profound impact on this evolution is the alternation of generations with the formation of multicellular bodies in both, the haploid (1n) and diploid (2n) generation of their life cycle. This invention facilitated adaptations and may have been instrumental in the ascent to terrestrial dominance. The overall aim of this project was to examine the genetic basis underlying the alternation of generations. To this end, I examined the function of the single full-length KNOX1 ortholog in the haploid-dominant liverwort Marchantia polymorpha. M. polymorpha was employed due to its unique intermediary position between Charophytes and vascular plants, its low genetic redundancy as well as increasing availability of genetic manipulation techniques. The results of this studies were combined with findings on MpKNOX2 and MpBELL genes that were obtained by cooperation partners. Together we showed that, upon fertilization, MpKNOX1 likely heterodimerizes with MpBELL3/4 to activate zygotic gene expression. MpKNOX1 which is maternally expressed (egg cell) is thereby absolutely required and loss-function results in zygotic arrest. On the other hand, MpBELL3/4 exhibit both, maternal and paternal (sperm) expression and loss-of either function results in variable zygotic and early embryonic arrest. Thus, similar to the unicellular chlorophyte alga Chlamydomonas, expression of paralogous KNOX and BELL TALE-homeodomain genes in M. polymorpha gametes primes the haploid-to-diploid transition. Co-expression of MpKNOX1 and MpBELL3/4 during later stages of diploid development is further consistent with an additional role in patterning the sporophyte. Taken together, those results suggests that (I) an ancestral genetic mechanism for activating diploid gene expression was retained in early diverging land plants and (II) this mechanism was co-opted and diversified to drive the evolution of complex sporophytic bodies.
Publications
- Plant Science’s Next Top Models. Annals of Botany
Cesarino, I., Dello Ioio, R., Kirschner, G. K., Ogden, M. S., Picard, K. L., Rast- Somssich, M. I., and Somssich, M.
(See online at https://doi.org/10.1093/aob/mcaa063) - Gamete expression of TALE class HD genes activates the diploid sporophyte program in Marchantia polymorpha. eLife 10:e57088
Dierschke, T., Flores-Sandoval, E., Rast-Somssich, M.I., Althoff, F., Zachgo, S., Bowman, J.L.
(See online at https://doi.org/10.7554/eLife.57088)
