Format: ORAL

Rafael Cruz1, Erica de Leau1, Erin Ryan1, Kuo Xu1, Zishan Fu1, Alexander J. Hetherington1

1 Institute of Molecular Plant Sciences, University of Edinburgh, Scotland, UK

Food-conducting cells are present in the major branches of the land plants phylogeny, and specialized phloem tissue is a predicted synapomorphy of the vascular plants. Little is known about the origins of phloem, and when looking at all groups, especially seed-free plants, we can find a great diversity of phloem structure considering the organization of sieve pores and associated parenchyma cells. However, the molecular toolkit necessary for phloem development is mostly described for flowering plants, particularly Arabidopsis. To better understand the evolution of genes related to phloem development in other groups, we conducted phylogenetic analyses of some genes related to phloem development. Our gene trees demonstrate that homologs of OCTOPUS (related to phloem cell polarization) and NAC 45/86 (related to cytoplasm and nucleus dissolution) appeared in the ancestor of vascular plants. The main regulator of Arabidopsis phloem development, ALTERED PHLOEM DEVELOPMENT, a MYB Golden-2-like protein, upregulates several genes in the phloem development pathway (including NAC 45/86). The ancestral copy of these proteins was present in the common ancestor of land plants. We are now exploring the expression of APL homologs in ferns and lycophytes, and we have identified seven and two APL homologs for the experimental models Ceratopteris richardii and Selaginella moellendorffii, respectively. Our preliminary data shows the expression of one of the APL homologs in the developing vascular system of S. moellendorffii. These findings provide insights into a possibly conserved regulatory network governing phloem development, shedding light on their evolution across diverse plant lineages.