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Abstract Structural variation in plant genomes is a significant driver of phenotypic variability in traits important for the domestication and productivity of crop species. Among these are traits that depend on functional meristems, populations of stem cells maintained by the CLAVATA-WUSCHEL (CLV-WUS) negative feedback-loop that controls the expression of the WUS homeobox transcription factor. WUS function and impact on maize development and yield remain largely unexplored. Here we show that the maize dominantBarren inflorescence3(Bif3) mutant harbors a tandem duplicated copy of theZmWUS1gene,ZmWUS1-B, whose novel promoter enhances transcription in a ring-like pattern. Overexpression ofZmWUS1-Bis due to multimerized binding sites for type-B RESPONSE REGULATORs (RRs), key transcription factors in cytokinin signaling. Hypersensitivity to cytokinin causes stem cell overproliferation and major rearrangements ofBif3inflorescence meristems, leading to the formation of ball-shaped ears and severely affecting productivity. These findings establishZmWUS1as an essential meristem size regulator in maize and highlight the striking effect of cis-regulatory variation on a key developmental program.
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Genetic dissection of cis -regulatory control of ZmWUSCHEL1 expression by type B RESPONSE REGULATORS
Abstract Mutations in cis-regulatory regions play an important role in the domestication and improvement of crops by altering gene expression. However, assessing the in vivo impact of cis-regulatory elements (CREs) on transcriptional regulation and phenotypic outcomes remains challenging. Previously, we showed that the dominant Barren inflorescence3 (Bif3) mutant of maize (Zea mays) contains a duplicated copy of the homeobox transcription factor gene ZmWUSCHEL1 (ZmWUS1), named ZmWUS1-B. ZmWUS1-B is controlled by a spontaneously generated novel promoter region that dramatically increases its expression and alters patterning and development of young ears. Overexpression of ZmWUS1-B is caused by a unique enhancer region containing multimerized binding sites for type B RESPONSE REGULATORs (RRs), key transcription factors in cytokinin signaling. To better understand how the enhancer increases the expression of ZmWUS1 in vivo, we specifically targeted the ZmWUS1-B enhancer region by CRISPR-Cas9-mediated editing. A series of deletion events with different numbers of type B RR DNA binding motifs (AGATAT) enabled us to determine how the number of AGATAT motifs impacts in vivo expression of ZmWUS1-B and consequently ear development. In combination with dual-luciferase assays in maize protoplasts, our analysis reveals that AGATAT motifs have an additive effect on ZmWUS1-B expression, while the distance separating AGATAT motifs does not appear to have a meaningful impact, indicating that the enhancer activity derives from the sum of individual CREs. These results also suggest that in maize inflorescence development, there is a threshold of buffering capacity for ZmWUS1 overexpression.
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- PAR ID:
- 10497697
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Plant Physiology
- Volume:
- 194
- Issue:
- 4
- ISSN:
- 0032-0889
- Format(s):
- Medium: X Size: p. 2240-2248
- Size(s):
- p. 2240-2248
- Sponsoring Org:
- National Science Foundation
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