Evolutionary Analysis and Functional Characterization of Selected SABATH Methyltransferases in Potato and Tomato

The plant SABATH family of methyltransferases are important for both modulating plant hormones and producing diverse secondary metabolites. While a growing list of SABATH methyltransferases has been characterized, function for many members of the SABATH family remains unknown. The goal of this dissertation is to expand our knowledge on the biochemical function, biological function and functional evolution of the SABTH family. The dissertation is arranged in four chapters. In the first chapter, a comprehensive review of the SABATH family was developed, covering their different biochemical functions, diverse biological roles, and representative three-dimensional structures. Their evolutionary relationship was studied in large-scale comparative genomic and phylogenetic analysis, providing insights into substrate specificities, reaction mechanisms, and evolutionary adaptations of this family. In the second chapter, a novel SABATH methyltransferase, phenylacetic acid methyltransferase (PAAMT), specifically methylating phenylacetic acid (PAA), was identified in potato, expanding the family's known catalytic functions and providing new insights into its functional evolution. The discovery of PAAMT further revealed that different auxin methyltransferase has strict substrate specificity, implying that auxins have complex and precise regulatory mechanisms in plants. In the third chapter, the salicylic acid methyltransferase (SlSAMT) as the key enzyme for methyl salicylate (MeSA) production in tomato roots was first identified. Next, the interaction between MeSA and root-knot nematodes (RKN, Meloidogyne spp.) was examined in transgenic tomato lines with varying SlSAMT levels. Higher MeSA levels increased RKN susceptibility, while lower levels conferred resistance. These findings highlight the complex interplay between plant secondary metabolites and pest resistance, suggesting potential strategies to enhance crop resilience through SAMT pathway modifications. The fourth chapter recaptures the main conclusions of this research and discusses future directions. In conclusion, the research presented in this dissertation enhances our understanding of the SABATH methyltransferases family and provides valuable insights for agricultural biotechnology and crop improvement.