Intron 3 of pyruvate orthophosphate dikinase (pdk i3) is used as a spacer sequence between antisense- and sense gene fragments in RNAi constructs to enhance vector stability. When expressed, the intron is spliced and the remaining RNA forms an inverted repeat double stranded structure triggering RNA silencing of the respective target gene. Pdk i3 was cloned into standard vectors used for gene silencing approaches such as pHELLSGATE.

The full gene sequence that includes intron 3 of the pyruvate orthophosphate dikinase (pdk i3) codes for the PPDK enzyme. PPDK is a key enzyme of the C4-photosynthesis mechanism. Its catalysis product phosphoenol pyruvate acts as an acceptor molecule for the primary CO2-fixation in mesophyll cells during C4-photosynthesis. Also in C3-plants PPDK isoforms are known where they most likely fulfil an anaplerotic function by providing carbon skeletons for amino acid biosynthesis.