A study has revealed new insights into the elusive process that allows a single hormone, known as auxin, to control nearly all aspects of plant growth and development. The research revealed a previously unknown mechanism, that has existed for over 500 million years, which plays key role in controlling auxin’s activity to suit a plant’s needs in different scenarios. The mechanism controls a diverse group of proteins, which are vital in regulating the activity of multiple genes involved in plant development when a cell detects auxin. Diverse processes Mutating these proteins in a maize plant showcased the dramatic impact they have on the plant’s shape – resulting in appearance similar to the iconic Truffula trees from Dr Suess’ book, The Lorax. Auxin is the chemical mastermind that controls a plant’s shape and size to suit its environment. Over hundreds of millions of years, it has allowed plants to thrive and spread across the planet.Previous studies had shown auxin can control so many diverse processes in plant development because it has a complex signalling system, which is regulated by several different proteins.But the mechanisms that control the levels of these signalling proteins, some of which are known as Auxin Response Factors (ARFs), inside plant cells has long been an important missing piece in the puzzle. Mutant maize plants: left to right – normal plant. (2 normal copies of the gene), heterozygous mutant (1 mutant copy of the gene, 1 normal copy of the gene), homozygous mutant (2 mutant copies of the gene). Mutant strains To tackle this an international team, led by researchers at the University of Edinburgh, compared mutant strains of maize and moss which are separated from each other by 500 million years of evolution.Auxin, and its complex signalling system, has helped to create the stunning diversity in the hundreds of thousands of plants species that exist today - from the smallest moss to the tallest oak tree.The team’s analysis revealed a specific region in a gene, that makes a sub-type of ARF proteins, known as class-B auxin response factors (ARFs), which is responsible for regulating the levels of class-B ARF protein accumulation in the cell.Although the DNA sequence of this region was found to vary across plant species, its function has been conserved and controls the rate at which class-B ARF proteins are degraded inside cells.The types and levels of ARFs present in plant cells influences which genes are turned on or off in response to auxin. Disrupted growth The team found that in maize mutating this region in a specific class-B ARF (ARF28) led to a rise in its protein levels, which disrupted nearly all aspects of the plant’s growth and development.The mutant maize plants showed dramatic differences in the position and number of their leaves, and resembled the mythical Truffula tree in the children’s book The Lorax by Dr Seuss.These plants had an elongated stem with leaves accumulated in a large tuft-like structure at the top of the plant.In contrast, maize plants normally have leaves extending throughout the length of their long stem, resulting in the familiar appearance of dense, tall leafy plants – often grown in rows in corn fields. Fine-tuning crops By better understanding the mechanism that controls how leaves are positioned researchers hope that in the future they will be able to fine-tune crops for improved yield and climate resilience. Auxin’s complex mechanism allows plants, which are fixed in place, to adapt to their changing environment - controlling the development of roots, stems and leaves throughout their lifespan to ensure their survival.The study, published in Nature Plants, was funded by UKRI, the Royal Society, National Science Foundation and National Institutes of Health.It also involved researchers from the University of California San Diego, Duke University, USDA Plant Gene Expression Centre, University of California Berkeley and LANGEBIO and CINVESTAV in Mexico. What’s so exciting about this project is that we were able to identify a key regulatory step in auxin signalling by comparing plant species that are separated by 500 million years of evolution! It really highlights the value of taking an evolution approach to better understand our crop plants. Dr Annis Richardson Senior Lecturer in Molecular Crop Science, Institute of Molecular Plant Sciences Related Links Dr Annis Richardson Comparative mutant analyses reveal a novel mechanism of ARF regulation in land plants, Nature Plants Publication date 02 May, 2025
