ABSCISIC ACID INSENSITIVE 5 fine-tunes expression of lipid body genes through modulating ABSCISIC ACID INSENSITIVE 3 binding strength

Seed development and germination are two important transitions in a plant's life cycle. During such transitions, extensive transcriptional regulation reprogramming is performed to support major changes in cellular, tissue, and physiological levels. Transcription factors contain diverse interacting partners for precise transcriptional regulations. Different combinations of interactors would affect temporal and spatial transcriptional regulations. While a large number of transcription factors (TFs) are involved in these transcriptional networks, in vivo investigation on how TF interaction dynamics affect transcriptional regulation in seed-to-seedling transition is lacking. ABSCISIC ACID INSENSITIVE 3 (ABI3) has played a major role serving as the center hub of these transcriptional networks during seed development. ABI3 has diverse interacting partners, including ABI5. The presence of these interacting partners allows ABI3 to bind to diverse cis-regulatory elements (CRE) in a precise manner. One of the processes collectively governed by ABI3 and ABI5 is nutrient deposition, including lipid storage. ABI3 and ABI5 regulate lipid body (LB) related genes such as oleosins for controlling LB dynamics. Notwithstanding, not much is known on ABI5's significance on ABI3's binding towards CREs. Here, we showed that ABI5 impacts ABI3's binding strength towards G-Box motifs. The interaction of ABI3 and ABI5 strengthens ABI3's binding towards ABI3 induced genes. We further demonstrated that ABI3 and ABI5 regulates far more LB related genes during seed development and germination, suggesting that ABI3 and ABI5's have a more precise role in regulating LB dynamics. Our results had further consolidated ABI5's role in ABI3's binding preferences and strength and its significance in controlling LB during seed development and germination.