Functional Characterization of Fasciclin-like Arabinogalactan Protein 1 Reveals Its Role in Biotic Stress Resistance and Morphological Adaptation in Tomato

Abstract The fasciclin-like arabinogalactan proteins (FLAs) have significant functions in plant development and adaptation to the environment. While numerous studies have elucidated the molecular roles of specific FLA genes in plant growth and development, there is limited knowledge regarding their contribution to plant tolerance against biotic stress. This study investigated the role of the SlFLA1 gene in tomato by overexpressing SlFLA1 and comparing its morphology to that of the wild type under biotic stress caused by Pseudomonas viridiflava and Meloidogyne incognita . Overexpression of SlFLA1 in tomato plants enhanced growth and reduced the size of bacterial lesions. The expression levels of SlFLA1 in lines FLA1-02, FLA1-10, and FLA1-12 were significantly elevated on the first day following the bacterial inoculation, while at day 21 day post-inoculation, SlFLA1 expression was significantly downregulated in lines FLA1-02 and FLA1-10 compared to wild-type. According to the reproduction index (RI) of nematodes, lines FLA1-04 and FLA1-12 exhibited similar levels of relative resistance, responding as moderately resistant, and suppressed nematode reproduction by 49% and 51%, respectively. In contrast, the other tomato lines exhibited a reduction of nematode reproduction by less than 50%. Gene expression analysis of markers associated with defense-related phytohormones revealed an increase in salicylic acid-induced PR‑1 and a decrease in jasmonic acid-induced PI and OPR3 in the inoculated roots overexpressing SlFLA1 at different times. The transgenic lines FLA1-10 and FLA1-02 exhibited a significantly higher trichome density compare to wild-type plants, while FLA1-17 exhibited the lowest. Collectively, our findings provide valuable insights into the role of the SlFLA1 gene in response to biotic stress caused by bacterial and nematode infections.