Overexpression of DWARF14-LIKE2 in Arabidopsis thaliana alters multiple traits related to plant morphology and osmotic and salt stress tolerance.

Karrikin signaling, mediated by the KARRIKIN INSENSITIVE 2 (KAI2) receptor, promotes seed germination, inhibits hypocotyl elongation, regulates root architecture, and mitigates abiotic stresses in plants. DWARF14-LIKE2 (DLK2), encoding a close homolog of KAI2, has been considered a marker gene in karrikin signaling pathway. However, the biological roles of DLK2 in plant growth, development, and abiotic stress responses are still unknown. Here, we found that DLK2 disruption significantly decreased hypocotyl elongation and cotyledon angle, while increasing root hair development and rosette leaf downward-curving. These phenotypes of dlk2 mutants are opposite to those observed in DLK2-overexpressing (DLK2-OE) plants. Furthermore, DLK2-OE plants showed significantly induced seed dormancy but reduced growth of cotyledon, rosette leaves, and primary and lateral roots in young seedlings. At later developmental stage, DLK2-OE plants displayed significantly reduced flowering and shoot branching, while showing increased stem diameter, final rosette and petal size, and seed size and weight. Transcriptome analysis of DLK2-OE leaves revealed that cell cycle, cell division, responses to abiotic stresses, and plant hormone pathways are regulated by DLK2. Consistently, DLK2-OE plants exhibited significantly smaller palisade mesophyll cell size, larger cell size in seed surface, and enhanced performance under osmotic and salt stresses. These findings demonstrate that DLK2 plays important roles in regulating plant growth and development, as well as plant stress responses, as their homologs KAI2 and D14, although with diverse functions in some growth-related traits.