ZmABI19 Takes Center Stage during Maize Grain Filling and Development

Yang and colleagues set out to untangle the network of transcription factors controlling O2 expression during maize seed development

By Tao Yang and Yongrui Wu, National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai 200032, China.

 Background. Maize seeds contain a large endosperm that serves as the primary storage organ to support embryo development and germination. In addition, the embryo also functions as a secondary storage organ in the grain. During grain filling, a group of spatiotemporally synchronized transcription factors (TFs, such as Opaque2, Prolamin Binding Factor1, NAC128, NAC130 and Opaque11) are expressed to regulate the biosynthesis of starch and storage proteins in the endosperm, while Viviparous1 is known to regulate the accumulation of storage proteins and oil in the embryo. Whether these TFs are coordinately regulated by upstream factors and the mechanism responsible for this process are currently largely unknown.

Question. What are the upstream factors and how do they coordinate expression of key factors required for maize seed development and grain filling?

Findings. We used the O2 promoter as bait to screen for the upstream factors that control O2 expression. We identified ZmABI19, a B3 domain-containing TF that binds to the promoter of and activates expression of the O2 gene. We showed that ZmABI19 is involved in regulating endosperm and embryo development, including starch, storage proteins, and lipid accumulation. We also demonstrated that ZmABI19 binds to the promoters of several other key TFs and other genes involved in grain filling and phytohormone responses to regulate their expression. We concluded that ZmABI19 is an upstream hub regulator of grain filling that coordinates embryo and endosperm development.

Next steps. To better understand the central role of ZmABI19 in maize seed development and grain filling, we will explore the posttranscriptional and translational regulation of ZmABI19 and other upstream factors that interact with ZmABI19 to coordinate endosperm and embryo development and initiate grain filling.

Tao Yang, Liangxing Guo, Chen Ji, Haihai Wang, Jiechen Wang, Xixi Zheng, Qiao Xiao, Yongrui Wu. The B3 Domain-Containing Transcription Factor ZmABI19 Coordinates Expression of Key Factors Required for Maize Seed Development and Grain Filling. The Plant Cell (2021),