Investigating the Role of Arabidopsis thaliana Phytolongins in Development and Stress Responses: A Mutant-Based Approach

Phytolongins are non-SNARE longin proteins found exclusively in land plants. In Arabidopsis thaliana, four isoforms have been identified, all encoded by single-exon genes. A recent study proposed their involvement in vesicular trafficking, based on localization analyses showing their presence along the endomembrane system. For this reason, phytolongins are hypothesized to play important roles in plant development and in responses to abiotic stresses. As these proteins remain poorly characterized, this thesis focuses on the functional analysis of two isoforms, PHYL1.1 and PHYL2.1, through phenotypic characterization of knock-out mutant lines. Parameters such as primary root length, root meristem organization, and germination rate were analysed under both control and salt stress conditions. Phenotypic analyses were complemented by gene expression studies aimed to understand how these proteins are transcriptionally regulated during stress responses. Our results show that PHYL1.1 and PHYL2.1 are crucial for proper development of the root apical meristem and root architecture; in addition, germination is also affected in the mutant lines, supporting their proposed role in developmental processes. Moreover, transcriptional analyses revealed a strong upregulation of all phytolongin isoforms during the early response to salt stress. These findings contribute to clarifying the essential roles of phytolongins in key biological processes such as plant development and stress adaptation.