Molecular genetic basis of pod corn (Tunicate maize)

Area of Science:

• Genetics
• Plant Biology
• Maize Research

Background:

• Pod corn is a maize (Zea mays) mutant characterized by kernels enclosed in glumes.
• This trait is controlled by the dominant Tunicate (Tu) locus, a subject of genetic study for decades.
• Previous research indicated complexity at the Tu locus, but molecular underpinnings were unknown.

Purpose of the Study:

• To elucidate the molecular basis of the pod corn mutation.
• To identify the specific gene(s) and regulatory mechanisms responsible for the Tunicate phenotype.

Main Methods:

• Comparative genetic analysis of wild-type and pod corn maize lines.
• Gene expression profiling to detect ectopic gene activity.
• Molecular characterization of the Tunicate (Tu) locus.

Main Results:

• Pod corn is caused by a cis-regulatory mutation and duplication of the ZMM19 MADS-box gene.
• Wild-type ZMM19 is expressed only in vegetative tissues.
• In pod corn, mutated and duplicated ZMM19 is ectopically expressed in reproductive organs (inflorescences).

Conclusions:

• The Tunicate phenotype in maize arises from altered ZMM19 gene regulation and copy number.
• Ectopic expression of ZMM19 in inflorescences confers vegetative characteristics to reproductive structures.
• This provides a molecular explanation for a classic maize morphological mutant.