Functional Analysis of CbbHLH35 Reveals Its Role in Drought and Cold Stress Tolerance in Caladium bicolor

Caladium bicolor is an important ornamental foliage plant; however, its tropical origin makes it highly sensitive to environmental stresses such as drought and low temperature, which limits its cultivation and industrial development. Basic helix–loop–helix (bHLH) transcription factors play key roles in plant responses to abiotic stresses, but their functions in C. bicolor remain largely unknown. Here, a bHLH transcription factor gene, CbbHLH35, was cloned from C. bicolor, and its sequence characteristics, subcellular localization, expression patterns, and potential roles in stress responses were analyzed. The results showed that CbbHLH35 contains a conserved bHLH domain and is localized in the nucleus. qRT-PCR analysis revealed that CbbHLH35 is expressed in different tissues, with the highest expression in tubers, and is significantly induced by methyl jasmonate (MeJA), abscisic acid (ABA), drought, and low-temperature treatments. Transgenic C. bicolor plants overexpressing CbbHLH35 were generated and subjected to drought and cold stress. Compared with control plants, the overexpression lines showed higher chlorophyll content and POD activity but lower electrolyte leakage and MDA content, indicating enhanced drought and cold tolerance. These results suggest that CbbHLH35 plays a positive role in regulating drought and cold tolerance in C. bicolor and represents a promising candidate gene for the molecular breeding of stress-resistant cultivars.