Balancing starch and protein in the maize endosperm

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Ning et al. identify a transcription factor responsible for modulating nitrogen and carbon metabolism in response to nitrogen availability.

 Background: Starch and protein are the main components of maize (Zea mays) endosperm. Nitrogen (N) fluctuation affects starch and protein levels in the endosperm. Earlier work in maize indicated that several transcription factors (TFs), such as Opaque 2, prolamin-box binding factor 1 (PBF1), Opaque11, and ZmbZIP22 regulate the expression of genes related to starch and protein metabolism in maize endosperm. However, whether there are any TFs responsible for altering protein and starch contents in maize endosperm under limited N conditions, and the corresponding regulatory mechanisms, remain largely unknown.

Question: Are there any TFs responsible for altering starch and protein levels in maize endosperm under N deficiency conditions. If so, how does this regulation work?

Findings: We observed that N deficiency affected the expression of many key genes in N and carbon (C) metabolism in the developing endosperm of maize and that P-box motifs were enriched in the promoter regions of these key genes associated with N and C biosynthesis and metabolism. The loss of PBF1 led to altered accumulation of starch and protein in maize endosperm. Notably, even though PBF1 protein levels remained stable under different N conditions, PBF1 bound different sets of target genes, especially genes related to the biosynthesis and accumulation of N and C storage products. We also demonstrated that PBF1 repressed the expression of Su1 and Sbe2b under normal N supply. We concluded that PBF1 is involved in modulating N and C metabolism during maize endosperm development in an N-dependent manner.

Next steps: To better understand the mechanisms of PBF1 in regulating the balance of protein and carbohydrate storage in an N dependent manner, we will explore the posttranscriptional and/or translation regulation of PBF1 and identify other transcript factors that potentially interact with PBF1 to coordinate the balance of storage protein and starch components under different N conditions.

Reference:

Lihua Ning, Yuanchong Wang, Xi Shi, Ling Zhou, Min Ge, Shuaiqiang Liang, Yibo Wu, Tifu Zhang, Han Zhao (2022). Nitrogen-dependent binding of the transcription factor PBF1 contributes to the balance of protein and carbohydrate storage in maize endosperm. Plant Cell. https://doi.org/10.1093/plcell/koac302