A naturally integrated RolD-like gene in sweet potato mediates stress-responsive pathways

Sweet potato (Ipomoea batatas), a globally significant staple crop, exhibits remarkable adaptability to various environmental conditions, largely due to its genetic diversity. Recent studies have revealed the presence of naturally integrated Agrobacterium cellular T-DNAs (cT-DNAs) within the sweet potato genome, suggesting their possible role in the evolution and adaptation of sweet potato. In this study, we characterize a newly identified open reading frame (ORF) within the cT-DNA2 region of I. batatas, which encodes a homolog of the A. rhizogenes rolD gene. This ORF encodes a RolD-like protein with ornithine cyclodeaminase (OCD) activity, a key enzyme in proline biosynthesis. Functional assays confirmed that the recombinant RolD-like protein exhibits ornithine-dependent NAD⁺ reduction, similar to the product of the rolD gene. Notably, rolD-like gene expression was strongly up-regulated by methyl jasmonate treatment, as well as in response to abiotic stresses such as heat, cold, salt, drought, high light, and UV radiation. Overexpression of this rolD-like gene in Arabidopsis thaliana resulted in delayed flowering, shortened siliques, and reduced seed production, along with enhanced proline accumulation, indicating its role in stress response mechanisms. These findings suggest that the natural integration of this rolD-like gene may contribute to the sweet potato's resilience to abiotic stresses, offering potential for the development of improved cultivars with enhanced stress tolerance.