Integrated of metabolome and transcriptome analysis reveals the effect of artificial light at night on Platanus...

Artificial light at night (ALAN) and its associated biological impacts have regularly been characterized as predominantly urban issues. ALAN delays the senescence of plane tree leaves in cities, resulting in the longer retention of green leaves. Some studies have described the effects of ALAN on plane trees at the physiological and biochemical levels. However, there is a lack of research at the molecular level.

In this study, we performed metabolic and transcriptomic analyses on plane green leaves with and without streetlight, as well as natural yellowing leaves away from the streetlight. In green leaves exposed to streetlights, numerous genes associated with auxin and cytokinins that inhibit leaf senescence were activated, while most genes associated with salicylic acid, jasmonic acid, ethylene and brassinolide that promote senescence were suppressed. Some candidate senescence-associated genes (SAGs) were identified, and brassinolide (6alpha-hydroxy-castasterone and castasterone), jasmonic acid ((-)-jasmonic acid and methyl jasmonate) and most flavonoids were significantly enriched in yellowing leaves. Combined analyses of transcriptome and metabolome data revealed that compared with the two green leaf groups, biosynthesis of amino acid, phenylpropanoid biosynthesis, tryptophan metabolism and flavonoid biosynthesis were the most significantly enriched metabolic pathway in yellowing leaves. Especially for phenylpropanoid biosynthesis and flavonoid biosynthesis related to leaf yellowing pigment accumulation, most of DEGs and DAMs are upregulated in yellowing leaves, but downregulated in green leaves under streetlight.

Our results indicate that ALAN retarded plant leaf senescence mainly by altering plant hormone levels and inhibiting metabolic pathways such as flavonoid biosynthesis, betalain biosynthesis, caffeine metabolism and phenylpropanoid biosynthesis. This study provides insights into how streetlights affect plane trees.