Recent studies have shown that a group of proteins known as COI1, which were previously linked to defense functions in various plant types like Arabidopsis and rice, mainly governs the growth of maize (corn). This insight could pave the way for creating stronger and more efficient maize strains.
Maize (corn) is a crucial staple crop worldwide and has been the subject of extensive research. Nonetheless, many genetic factors that control its growth and development are still not well-understood. The latest research has identified that the COI1 protein family, known for their role in plant defense in species like Arabidopsis and rice, primarily influences maize growth. This finding could help in breeding more resilient and productive maize cultivars.
In the realm of plants, growth and defense often work against each other. When a plant prioritizes defending itself from pests or diseases, its growth generally suffers due to competing proteins. These proteins include JAZ (jasmonate ZIM-domain) that repress defense genes and DELLA proteins that inhibit growth. COI proteins play a key role in balancing these activities by degrading JAZ proteins.
The study examined six COI proteins in maize, categorized into two groups: COI1 and COI2. Researchers created mutant plants that were missing one, two, or all four COI1 proteins. However, it was impossible to generate mutants lacking both COI2 proteins, as this caused lethal effects in pollen development. This finding underscores the essential role COI2 proteins play in male reproduction and pollen formation in maize.
The research also uncovered surprising results regarding plants missing all four COI1 proteins. “These ‘COI1-4x’ mutants showed a significant decrease in growth compared to normal maize plants,” stated Leila Feiz, the lead author of the recent study published in The Plant Cell. “This was unexpected since COI mutations in other species like Arabidopsis and rice typically lead to taller plants.”
Feiz further explained, “In C3 coi mutant plants such as Arabidopsis, the absence of JAZ degradation by COI traps DELLA proteins. This causes the activation of gibberellic acid-driven growth genes, usually suppressed by DELLA. In contrast, wild-type plants continuously treated with jasmonic acid grow shorter, as COI recognizes jasmonic acid and degrades JAZ. This degradation activates defense genes and releases DELLA from JAZ, thus curbing growth. Unlike COI mutants of Arabidopsis and rice, which grow taller than their wild-type counterparts, the maize quadruple COI1 mutant displayed shorter growth in comparison to both the wild-type and double mutant plants.”
Additional investigations suggested that COI1 proteins in maize may have adapted a new role: the degradation of DELLA proteins that hinder plant growth. Feiz theorizes that by eliminating these growth-inhibiting DELLAs, COI1 proteins allow maize to thrive even under high levels of jasmonic acid, which is common in plants from hot and dry climates where C4 plants like maize and sugar cane originated. This new function of COI1 in managing DELLA levels and promoting growth could be an evolutionary adjustment that has enabled maize, and perhaps other C4 plants, to succeed in harsh environments — a crucial factor in the evolution of C4 plants. By separating growth and defense mechanisms, maize and other C4 plants, including sorghum, can sustain healthy growth even when subjected to environmental challenges that would typically hinder growth.
The origin of this research project is quite fascinating. It began nearly five years ago when a few single-mutant plants were salvaged from an abandoned project. Kevin Ahern, who was then a graduate student and field manager in Georg Jander’s lab at the Boyce Thompson Institute, managed to pollinate and gather seeds from these plants. Eventually, Feiz, a researcher in Jander’s lab, took over the mutant seeds to advance the project. Throughout this study, she worked alongside several other scientists, including Shan Wu, a postdoctoral researcher in Zhangjun Fei’s lab, who assisted with the analysis of extensive RNA sequencing data.
This research opens doors for improving crop strength and yield by shedding light on how COI proteins interact with DELLA proteins and other elements of the plant’s signaling pathways. It demonstrates how fundamental research in plant science can reveal intriguing evolutionary adaptations and lead to significant agricultural developments.
The study received funding from the NSF and USDA.
