By the end of the 21st century, Earth is expected to be home to 11 billion people. As the demands on agricultural production grow, climate change is affecting growing seasons, crop yields and plant health, making food security one of the biggest challenges.
At a greenhouse laboratory atop the Sixth Street Garage at the University of Arizona, a team of faculty, graduate and undergraduate students is diving into the unexplored, microscopic universe of the maize genome to shed new light on the developmental mechanisms of this important food crop.
Around the world, more than 50 percent of calories in the human diet come directly or indirectly from rice, wheat and maize. Of these, maize is the highest-producing cereal commodity, according to 2014 figures from the Food and Agriculture Organization of the United Nations. An understanding of how plant seed can be modified to increase yield under environmental stress could lead to strategies to increase agricultural yields in the context of shrinking arable land, major changes in the climate and the ever-growing population.
The main nutritive and economic value of maize lies in the kernel's endosperm, or the seed-storage compartment, that provides proteins and carbohydrates for human diets and animal feed, as well as raw materials for industrial products. The size and quality of the endosperm can make or break the survival of the seedling during germination and affect crop yields, yet little is known about the genetic mechanisms that drive endosperm development.
The National Science Foundation has funded an ongoing five-year project totaling nearly $7.5 million for a consortium of four universities to decipher how the maize kernel develops during the first 16 days after pollination, when it is most susceptible to drought and other stresses.
Headed by Ramin Yadegari at the UA with Gary N. Drews at the University of Utah, Philip W. Becraft at Iowa State University and Joanne M. Dannenhoffer at Central Michigan University, the project builds on a previous NSF grant that identified gene networks associated with creating various cell types within the endosperm and how genes are activated during endosperm development.
"In this project, we want to know how the endosperm becomes the storage compartment of the kernel," said Yadegari, a professor in the School of Plant Sciences in the UA College of Agriculture and Life Sciences. "We want to go into greater detail as to which genes have to be activated at what time in the endosperm, to pick up sugar from the mother plant and use it in developing the storage compartment of the kernel. High storage content is what makes maize kernels so valuable."
In only four to eight days after pollination, a complex series of developmental activities takes place within the endosperm. Between 10,000 and 20,000 genes are expressed within this short time frame. But this activity has an enormous impact on kernel size and the type of storage material it accumulates.
"We want to uncover the gene regulatory networks of endosperm development in maize to improve the yield and also the seed quality, to help it survive in a stressful environment with extreme drought stress and high temperatures," said Choong-Hwan Ryu, a postdoctoral research associate in plant sciences. "We can adjust our controls of the gene expression to improve drought tolerance. I am working to uncover that regulatory network in maize."
An R&D and Educational Enterprise
Back in the laboratory, the research team is using high-powered sequencing technology and laser-capture microdissection on plant samples to compile an atlas of gene expression profiles for each of the cell types involved in early endosperm development in maize, and conduct network analysis to discover how key developmental processes are regulated. It also is studying the impact of drought on these networks to understand exactly how yields are reduced.
"A lot of the transcription factor proteins I've looked at do interact with each other, meaning a lot of complex interaction is going on to make the maize kernel," said Pierce Longmire, an undeergraduate studying molecular and cellular biology, who is cloning maize genes to see how they are expressed in the kernel. "Many of these proteins haven't been described before — we're the first ones to actually see some of these interactions."
Tricia Ramsay, majoring in biochemistry and molecular and cellular biology with a plant sciences minor, hopes to go into graduate research.
"So far, I have discovered science is 90 percent failure and 10 percent results. You just work and work and sometimes it turns out well and other times you are problem solving the whole time," she said. "I'm waiting for that moment when I know something nobody else knows for at least 10 seconds, but I haven't gotten to that point. I'm looking for that place where you've actually found something that hasn't been discovered before."
Better-Adapted Crops in Less Space
The world has increasingly limited amounts of space to grow ever-larger amounts of food. To assist in developing solutions, all data from this project are deposited continuously in designated online resources that can be accessed freely. This is fundamental research, but there are people working in applied areas, and breeders, who will take the knowledge and extend it. Maize growers are major supporters of this type of research and also breeders, basic plant scientists and others, according to Yadegari.
"The value is building the basic knowledge base, finding novel things that allow us to understand the plant's functional processes such as seed development that can be directly used by universities and agricultural companies to create new accessions that would benefit farmers," Yadegari said.
"For me, a driving interest is — rather than having a uniform set of genetic material you can send all over the world — to identify genetic stocks, accessions that are highly adaptable to the local environment. Maize accessions that can be grown in parts of Africa that are highly adaptable to an individual area, for example. When you look at the diversity of maize accessions that are available, we can grow different types in different parts of the world — a significant diversity that people and researchers can use."