MERISTEM L1-like, a HD-Zip IV transcription factor, regulates long-stalked glandular trichome development in <i>Nicotiana tabacum</i>

Glandular trichomes are specialized epidermal structures that contribute to plant defense by secreting protective metabolites. In this study, we investigated the functional role of the homeobox-leucine zipper protein MERISTEM L1-like (ML1), a class IV HD-Zip transcription factor, in regulating glandular trichome development in Nicotiana tabacum. Using an integrated approach combining transcriptomics, reverse genetics, functional genomics, and protein interaction assays, we found that ML1 is essential for the formation of long-stalked glandular trichomes. Loss-of-function mutation in ML1 leads to reduced density of long-stalked glandular trichomes and altered metabolite profiles, underscoring its regulatory role in both trichome initiation and secondary metabolism. Furthermore, ML1 interacts with the R2R3-MYB transcription factor REGULATORY AXILLARY MERSITEM 2 (RAX2) to jointly modulate trichome developmental genes. RNA-sequencing analysis revealed an extensive transcriptional network influenced by ML1, offering novel insights into the molecular mechanisms underlying glandular trichome formation. The results of this study should inform future biotechnological approaches aimed at improving pest resistance and enhancing metabolite production in Solanaceae crops.