Roles of UV-damaged DNA binding protein 1 (DDB1) in epigenetically modifying multiple traits of agronomic importance in tomato

Epigenetic regulation participates broadly in many fundamentally cellular and physiological processes. In this study, we found that DDB1, a protein originally identified as a factor involved in DNA repairing, plays important roles in regulating organ size, growth habit and photosynthesis in tomato via an epigenetic manner. We generated transgenic tomato plants overexpressing an alternatively spliced DDB1 transcript (DDB1F, prevalently present in tomato tissues) and found the primary transformants displayed small-fruited "cherry tomato" in companion with strikingly enhanced shoot branching and biomass, dark-green leaves with elevated chlorophyll accumulation, and increased soluble solids in fruits. Significantly, these phenotypic alterations did not segregate with the DDB1F transgene in subsequent generations, suggesting that the effect of DDB1F on multiple agronomic traits is implemented via an epigenetic manner and is inheritable over generations. We speculate that DDB1, as a core subunit in the recently identified CUL4-based E3 ligase complex, mediates the 26S proteasome-dependent degradation of a large number of proteins, some of which might be required for perpetuating epigenetic marks on chromatins.