Investigating Plant Stem Cells’ Role in Yielding More and Bigger Fruit

Madelaine Bartlett
Madelaine Bartlett

Madelaine Bartlett, biology, and plant genome scientist colleagues elsewhere have received a four-year, $4 million grant from the National Science Foundation ($812,000 to Bartlett) to study the genes that regulate plant stem cell biology and the role they play in yielding more and bigger fruit.

One goal is to experimentally speed up the mutation process, she says. “Instead of waiting for the next thousand years to see what new mutations arise in these genes, we will accelerate evolution in a very controlled and intelligent way to create genetic diversity for use by traditional plant breeders.”

The evolutionary biologist adds, “All the plants we eat have been domesticated, that is, selected by ancient farmers to be more convenient to grow and to yield more food. Because of all we know about how evolution works, we’ll use the same tools that nature does to create new genetic diversity.”

The research collaboration, which will focus on tomatoes, corn and the model plant Arabidopsis thaliana, is led by principal investigator David Jackson of Cold Spring Harbor Laboratory, N.Y. Others on the team are colleague Zachary Lippman at Cold Spring, Bartlett and Zachary Nimchuk of the University of North Carolina. In earlier studies by the Jackson lab published in Nature Genetics with Bartlett as a co-author, the researchers showed that weak alleles of a gene in the CLAVATA gene network can enhance fruit yield in corn. The researchers plan to build on that success.

Bartlett says that it has become clear from Jackson and Lippman’s earlier work that during the domestication of both tomatoes and corn some CLAVATA network gene variants were selected, leading to bigger tomatoes and more corn. “Some farmer saw this, and the variant was passed down. We now know that the genes in both cases are in the same network.”

Her lab’s role will be to uncover the evolutionary history of the CLAVATA network and how its genes are regulated. “They seem to have been important in domestication and plant evolution more broadly,” she adds. “As humans we are completely dependent on plants and on these genes in particular. Every single grain of rice and corn, every single tomato on this planet is dependent on this cluster of stem cells.”

CLAVATAmeans “club-like,” to describe the misshapen cluster of too many stem cells at the plant’s growing tip in CLAVATA genetic mutants. Bartlett says in ancient plants mutations in CLAVATA-networkgenes created “weak alleles,” versions of the genes that still functioned, but differently. “The advantage of a weak allele is that the gene isn’t broken,” Bartlett explains. “Its expression is just turned up or down slightly so growth regulation is still healthy and well balanced but may yield bigger and more fruit or corn.”

She and colleagues will use a CRISPR/Cas9 multiplex knockout strategy to make semi-random mutations across gene regulatory sequence regions. They will screen these to recover weak alleles with enhanced yield traits.

“We want to generate genetic diversity for breeders, so they have new material to work from,” Bartlett says. “Right now, they have to wait for mutations to randomly occur, which of course can take a very long time. We will be like those ancient farmers except we are using more modern tools. From our work, somebody in the future will be able to give plant breeders access to variants they might be interested in for growing bigger fruit and more fruit.”

The team also plans outreach activities such as open house displays and lab visits in rural farm communities in New York, Massachusetts and North Carolina to illustrate how plant genomics research can be useful in agriculture.

Bartlett, who arrived on campus in 2014, has an undergraduate degree from the University of the Witwatersrand, South Africa. She earned her Ph.D. in the evolution of flower development in bananas and gingers at the University of California Berkeley and completed postdoctoral studies at Brigham Young University in maize genetics and grass evolution.