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Proc Natl Acad Sci U S A. 2019 Jun 4;116(23):11223-11228. doi: 10.1073/pnas.1904995116. Epub 2019 May 20.

NAC-type transcription factors regulate accumulation of starch and protein in maize seeds.

Author information

1
Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ 08854.
2
National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology & Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 200032 Shanghai, China.
3
Chinese Academy of Sciences Center for Excellence in Molecular Plant Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 200032 Shanghai, China.
4
Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ 08854; messing@waksman.rutgers.edu.

Abstract

Grain starch and protein are synthesized during endosperm development, prompting the question of what regulatory mechanism underlies the synchronization of the accumulation of secondary and primary gene products. We found that two endosperm-specific NAC transcription factors, ZmNAC128 and ZmNAC130, have such a regulatory function. Knockdown of expression of ZmNAC128 and ZmNAC130 with RNA interference (RNAi) caused a shrunken kernel phenotype with significant reduction of starch and protein. We could show that ZmNAC128 and ZmNAC130 regulate the transcription of Bt2 and then reduce its protein level, a rate-limiting step in starch synthesis of maize endosperm. Lack of ZmNAC128 and ZmNAC130 also reduced accumulation of zeins and nonzeins by 18% and 24% compared with nontransgenic siblings, respectively. Although ZmNAC128 and ZmNAC130 affected expression of zein genes in general, they specifically activated transcription of the 16-kDa γ-zein gene. The two transcription factors did not dimerize with each other but exemplified redundancy, whereas individual discovery of their function was not amenable to conventional genetics but illustrated the power of RNAi. Given that both the Bt2 and the 16-kDa γ-zein genes were activated by ZmNAC128 or ZmNAC130, we could identify a core binding site ACGCAA contained within their target promoter regions by combining Dual-Luciferase Reporter and Electrophoretic Mobility Shift assays. Consistent with these properties, transcriptomic profiling uncovered that lack of ZmNAC128 and ZmNAC130 had a pleiotropic effect on the utilization of carbohydrates and amino acids.

KEYWORDS:

gene regulation; maize endosperm; protein; starch synthesis

PMID:
31110006
PMCID:
PMC6561305
[Available on 2019-11-20]
DOI:
10.1073/pnas.1904995116

Conflict of interest statement

The authors declare no conflict of interest.

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