BEGIN:VCALENDAR VERSION:2.0 PRODID:icalendar-ruby CALSCALE:GREGORIAN METHOD:PUBLISH BEGIN:VTIMEZONE TZID:Europe/Vienna BEGIN:DAYLIGHT DTSTART:20260329T030000 TZOFFSETFROM:+0100 TZOFFSETTO:+0200 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3 TZNAME:CEST END:DAYLIGHT BEGIN:STANDARD DTSTART:20261025T020000 TZOFFSETFROM:+0200 TZOFFSETTO:+0100 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10 TZNAME:CET END:STANDARD END:VTIMEZONE BEGIN:VEVENT DTSTAMP:20260925T123456Z UID:1792396800@ist.ac.at DTSTART:20261019T100000 DTEND:20261019T110000 DESCRIPTION:Speaker: Adrijana Smoljan\nhosted by Andela Saric\nAbstract: Th e successful colonization of terrestrial environments by plants required t he evolution of developmental and signalling mechanisms that enabled adapt ation to increasingly heterogeneous environments. Among these innovations\ , environmental sensing and directional transport of the plant hormone aux in have played central roles in shaping plant morphology and adaptation to external cues. However\, the evolutionary origins of these regulatory sys tems remain incompletely understood. This thesis investigates two fundamen tal evolutionary questions: when auxin transport mediated by PIN auxin tra nsporters emerged during plant evolution and how MIZ1 proteins acquired th eir role in root hydrotropism.The first part of the thesis examines the ev olution of PIN-FORMED (PIN) auxin transporters using chlorophyte algae and other early-diverging eukaryotic lineages. Physiological analyses demonst rated that chlorophyte algae exhibit concentration-dependent responses to exogenous auxin and possess both passive and energy-dependent auxin transp ort systems\, indicating that fundamental aspects of auxin biology predate the emergence of land plants. Phylogenetic\, structural\, and functional analyses revealed that PIN homologs are broadly distributed across diverse eukaryotic lineages and retain the characteristic PIN protein fold and pr edicted auxin-binding residues. However\, heterologous expression assays i n Xenopus laevis oocytes\, tobacco BY-2 cells\, and Arabidopsis thaliana d emonstrated that these ancestral PIN homologs lack the directional auxin e xport activity characteristic of canonical land plant PIN proteins. Instea d\, they predominantly localize to the endoplasmic reticulum and display l imited or no auxin transport activity\, suggesting that ancestral PIN prot eins primarily functioned in intracellular auxin homeostasis before being recruited for polar auxin transport during land plant evolution.The second part of the thesis investigates the evolutionary diversification of MIZ1 proteins\, key regulators of root hydrotropism in Arabidopsis thaliana. Ph ylogenetic analyses showed that MIZ1 proteins are conserved throughout lan d plants but absent from green algae\, indicating that the protein family originated early during terrestrialization. Although MIZ1 homologs from Ma rchantia polymorpha\, Physcomitrium patens\, Selaginella moellendorffii\, and Amborella trichopoda displayed highly conserved predicted structures a nd endoplasmic reticulum localization\, none were able to complement the h ydrotropic or cytokinin-response defects of the Arabidopsis miz1 mutant. F unctional characterization of Marchantia revealed that MpMIZ1a regulates t hallus development\, cytokinin-dependent growth responses\, expression of cytokinin biosynthetic genes\, and normal sporophyte development\, indicat ing an ancestral role in cytokinin homeostasis and developmental regulatio n rather than hydrotropism. Furthermore\, protein docking predicted an int eraction between MpMIZ1a and its native cytokinin receptor MpCHK\, which w as supported experimentally by bimolecular fluorescence complementation (B iFC). BiFC revealed interactions between the cognate protein pairs MpMIZ1a –MpCHK and AtMIZ1–AtAHK4\, whereas little or no interaction was detect ed for the reciprocal cross-species combinations MpMIZ1a–AtAHK4 and AtMI Z1–MpCHK. This species-specific interaction compatibility provides a pot ential mechanistic explanation for the inability of MpMIZ1a to functionall y complement the Arabidopsis miz1 mutant. Together\, the findings present ed in this thesis demonstrate that both auxin transport and MIZ1 protein f unction evolved through the progressive modification and recruitment of an cestral molecular components. The results support a model in which early P IN proteins primarily regulated intracellular auxin homeostasis before evo lving into specialized plasma membrane auxin exporters\, while MIZ1 protei ns originated as endoplasmic reticulum-associated regulators of cytokinin- dependent development and were subsequently recruited into the hydrotropic signalling pathway of seed plants. By integrating comparative genomics\, structural biology\, molecular genetics\, live-cell imaging\, and physiolo gical analyses across diverse evolutionary lineages\, this work provides n ew insights into the molecular innovations that contributed to the success ful colonization of terrestrial environments and the evolution of developm ental plasticity in land plants. LOCATION:Central Bldg / O1 / Mondi 2a (I01.O1.008)\, ISTA ORGANIZER: SUMMARY:Adrijana Smoljan: Thesis Defense: Evolution of auxin transport and MIZ1-mediated developmental responses during plant adaptation to terrestri al environments URL:https://talks-calendar.ista.ac.at/events/6666 END:VEVENT END:VCALENDAR