Sucrose and ABA regulate starch biosynthesis in maize through a novel transcription factor, ZmEREB156

Starches produced by higher plants function as seed storage reserve carbohydrates and are the most important dietary source of energy for humans, representing a major proportion of daily caloric intake1. The storage starches produced in maize endosperm amyloplasts account for over 90% of the world market for starch2. Starch biosynthesis and accumulation is an important process that not only determines grain yield but also influences grain quality3. Starch biosynthesis in the cereal endosperm requires the coordinated activities of several major enzymes, including adenosine 5′ diphosphate-glucose (ADP-Glc) pyrophosphorylase (AGPase), starch synthase (SS), starch branching enzyme (SBE), and starch debranching enzyme (DBE)4,5. However, the molecular mechanisms that regulate the gene expression of the network of starch synthesis enzymes remain unclear6. Sucrose (Suc) is an important source of energy and carbon skeletons for plant growth and development, but also acts as an important signal that modulates developmental and metabolic processes in the plant life cycle7,8. It has been reported that sucrose acts as a signalling molecule for genes critical to starch biosynthesis in different species9,10. Sucrose is the only sugar capable of inducing the expression of the AGPase large subunit genes (iAGPLI-1 and ApL3) in sweet potato and Arabidopsis thaliana11,12. Both starch synthase (GBSSI) and β-amylase genes are also reportedly induced by sucrose in sweet potato13,14. Kim and Guiltinan showed that expression of the Sbe1 gene was induced by sucrose and was regulated through mEmBP-1, a bZIP transcription activator, in suspension-cultured maize endosperm cells, suggesting a possible regulatory role of the C-box present in the Sbe1 promoter from −227 to −22015. Sun found that the transcription factor SUSIBA2, induced by sucrose, belongs to the WRKY protein family and binds to sucrose-responsive elements (SURE) and W-box elements but not to the SP8a element in the iso1 promoter16. These reports confirm the importance of sucrose as a signalling molecule, but the molecular mechanism is not fully understood. In a previous study, we found that sucrose combined with abscisic acid (ABA) synergistically influenced expression of 15 starch biosynthetic genes in maize endosperm17. Few reports indicate that sucrose induces starch biosynthetic gene expression by interacting with ABA signalling pathways18,19,20,21. AtAPL3 and OsAPL3 expression increased in response to exogenous application of sucrose in Arabidopsis leaves and cultured rice cells, respectively20,21. In addition, their expression was further enhanced by co-treatment with ABA. However, the molecular mechanisms by which starch biosynthetic genes in maize endosperm are regulated by interaction with sucrose and ABA remain unclear. In the present study, maize endosperms 10 DAP (days after pollination) were treated with sucrose, ABA, or both, and then analysed by RNA sequencing (RNA-seq). Analysis of these gene sets identified different treatments of gene expression, including hundreds of transcription factor genes. We found that some transcription factor genes were affected synergistically by Sucrose and ABA. We hypothesized that at least one transcription factor gene would be involved in maize endosperm starch synthesis by synergistic effect of sucrose combined with ABA. The results lay a foundation for understanding the underlying mechanisms that control seed yield and quality.