Multiple overlapping copies of a red corn silk tassel on an ear of corn in a field

Plants carry multiple gene copies — but why?

October 24, 2019

Plant geneticist Joe Gallagher, a postdoctoral researcher in evolutionary developmental biologist Madelaine Bartlett’s biology lab, recently received a coveted two-year postdoctoral fellowship from the U.S. Department of Agriculture (USDA) that includes salary and research support for his study of the evolution of duplicate growth repression genes. 

 

One of the unusual features of plants and a fact that non-biologists may not know about them is that they often have many sets of duplicate genes, Gallagher says, many more than they apparently need and more than other organisms, including humans. He says the repeated occurrence of this in land plants is “one of the great discoveries of the genomics era,” and is a very active research area at present. Most food crops either bear signatures of it from ancient times or are still in a duplicated state, he adds, but the mechanisms remain poorly understood. 

“We humans have exactly two copies of our genes,” he explains. “But in some plants there are as many as 12 copies or more. They are the results of ancient duplication, and any one of them can split off at any time, branch out and evolve to perform different functions and act in different areas of the plant. They can pick up new functions, which can lead the plant down new pathways of evolution.” 

One of his research goals is to better understand this redundancy, which may be conferred by polyploidy – when the plant has more than two sets of paired chromosomes. “If we can figure out how this is happening, it could have some fairly practical implications for agriculture,” the geneticist notes. “Many crop plants are polyploids or show a history of polyploidy,” he adds. 

Bartlett says, “Dr. Gallagher is a fantastic scientist, I’m lucky that he came to join my lab. His fellowship project is going to make an important contribution to the field of plant development and will have exciting implications for crop improvement and engineering.”  

Gallagher’s earlier work had focused on the effects of polyploidy on genomic diversity, transcription and gene expression in wild and domesticated cotton. In the Bartlett lab, he is now working on the evolution of the highly duplicated leucine-rich repeat receptor-like kinase (LRR-RLK) genes, which have many roles in plant development and defense, he notes. “Up to now, I’ve been doing evolutionary analysis of this pathway and these genes, and this new grant will allow me to branch into a new area with similar themes.” 

These new areas involve genes that control growth repression. Plants use growth repression to form shapes, for example, by turning off genes in a pathway that forms leaves, they can make a lobed leaf or a thin, lacy leaf. 

His work will focus on a growth repression function that regulates branching and flower development in the grasses, in particular corn. Normally, corn forms a male tassel and a female ear, but when the gene is broken, female parts form in the tassel alongside the male parts. “It’s a sign that the repression pathway failed,” Gallagher says. “It should have prevented the female parts from developing that much. Normally the female parts would be suppressed and only form in the ear.” 

Further, he will investigate the hypothesis that some growth repression genes have persisted since ancient times in groups or modules, units “that you can plug and play like a CD,” he notes. “We’re seeing these growth repression genes being used in different pathways and being recruited over and over again throughout evolution. We’ll look at a broad sample, in different plant species, at how they have changed and their role in plant development.” 

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