Trichomes are specialized epidermal appendages that serve as excellent models to study cell morphogenesis. Although the molecular mechanism underlying trichome morphogenesis in Arabidopsis has been well characterized, most of the regulators essential for multicellular trichome morphology remain unknown in tomato. In this study, we determined that the recessive hairless-2 (hl-2) mutation in tomato causes severe distortion of all trichome types, along with increased stem fragility. Using map-based cloning, we found that the hl-2 phenotype was associated with a 100 bp insertion in the coding region of Nck-associated protein 1, a component of the SCAR/WAVE complex. Direct protein-protein interaction was detected between Hl-2 and Hl (SRA1, specifically Rac1-associated protein) using yeast two-hybrid and co-immunoprecipitation assays, suggesting that these proteins may work together during trichome formation. In addition, knock-down of a HD-Zip IV transcription factor, HDZIPIV8, distorted trichomes similar to the hl-2 mutant. HDZIPIV8 regulates the expression of Hl-2 by binding to the L1-box in the Hl-2 promoter region, and is involved in organizing actin filaments. The brittleness of hl-2 stems was found to result from decreased cellulose content. Taken together, these findings suggest that the Hl-2 gene plays an important role in controlling multicellular trichome morphogenesis and mechanical properties of stems in tomato plants.

Within the canonical auxin signaling pathway, Auxin Response Factors (ARFs) are transcriptionally repressed by AUX/IAA proteins under low auxin conditions, and this repression is alleviated as auxin concentrations increase. By contrast, ARF3 functions as a central regulator of gynoecium morphogenesis in Arabidopsis via a non-canonical auxin-sensing mechanism that relies on dose-dependent modulation of its protein–protein interaction network. To investigate whether an analogous regulatory mechanism operates in tomato (Solanum lycopersicum), we identified the tomato ARF3 homolog (SlARF3) and utilized it as bait in a yeast two-hybrid (Y2H) screen. This screening approach yielded 137 positive clones, corresponding to 118 putative interacting proteins. Notably, all of these interactions were abolished in the presence of 3-indoleacetic acid (IAA), indicating that SlARF3 engages in auxin-sensitive protein–protein interactions and thereby mediates auxin-dependent signal transduction. Among these, we identified an auxin-sensitive interaction between SlARF3 and TM29, a central regulator of parthenocarpy, underscoring its critical role in this developmental pathway. Functional analyses further demonstrated that silencing SlARF3 induces parthenocarpic fruit formation. Taken together, these findings define a previously uncharacterized SlARF3-centered interaction network and provide a conceptual framework for elucidating non-canonical auxin signaling pathways underlying tomato development.

Emergence of adventitious roots (ARs) in partially submerged plants is a crucial morphological adaptation to flooding stress, although the underlying molecular mechanisms are not well understood. In the present research, we investigated the role of CsRBOHB-mediated reactive oxygen species (ROS) production in cucumber (Cucumis sativus L.). ROS specifically accumulated in the vascular tissues of partially submerged hypocotyls. Respiratory burst oxidase homologs (RBOHs) are enzymes that generate ROS. We found that a cucumber RBOH gene, CsRBOHB, was specifically induced in vascular cells by partial submergence. Knockout of CsRBOHB inhibited AR emergence, while overexpression of CsRBOHB enhanced it. Downregulation of an RBOHB homolog SlRBOHB in partially submerged tomato also inhibited AR emergence. Additionally, cucumber calcium-dependent protein kinase 2 (CsCDPK2) directly activated CsRBOHB in cucumber hypocotyls during AR emergence, and silencing it inhibited AR emergence under partially submerged conditions. These findings indicate that AR emergence in partially submerged cucumber is regulated by a CsCDPK-CsRBOHB pathway.