What makes plants change their growth habits?

A new study from the John Innes Centre explains why some plants grow tall, yet have relatives that stay close to the ground. The researchers set out to investigate the various growth habits of plants, including differences that exist even among closely related species. 

For example, plants belonging to the Brassica family include a widely variable assortment of heights, ranging from the compressed rosette growth of cabbages to tall crops such as oilseed rape.

The experts have identified the genes that control changes in growth habits. Using genetic analysis, microscopy, and a technique called ChIP sequencing, the team linked compact growth to two different types of genes, ATH1 and DELLA, which work in tandem.

When both types of genes are turned off, compact growth is converted to elongated growth. On the other hand, when the genes are active, either can stop the activity of well-known genes that normally promote elongated growth.

“It is well known that the way plants grow depends heavily on the environment. At the same time, each species of plant keeps its recognizable shape. We know a little about how responses to the environment are integrated with the genetic mechanisms that give plants their basic, characteristic shape, or morphology. Thanks to this study, we now understand how responses to the environment can be modified in specific parts of the plant to produce their characteristic shape,” explained study co-author Professor Robert Sablowski.

“It was exciting to see that a relatively small number of genetic changes can convert the plant’s growth habit from one like cabbage to one like oilseed rape. It remains to be seen whether comparable changes explain the differences in growth habit we see in nature.”

Previous research has shown that there is a similar mechanism of two genes that work together to control the growth habits of rice, which indicates this may be a common tool that controls plant architecture.

Genes that control plant height are important in agriculture. DELLA genes have been used extensively in crop breeding to improve yields.

By understanding the genes that regulate how tall a plant grows, experts can develop more reliable ways to improve the shape of crop plants. Going forward, the researchers are planning to explore how ATH1 is regulated.

“If we can alter the location or time when ATH1 is active, this could lead to useful ways to modify plant height and shape,” said study first author Dr. Mahwish Ejaz.

“We have shown that ATH1 and DELLA genes prevent stem growth in part by stopping the activity of genes that cause stems to elongate in response to light. But this is not the whole story – there are many other genes and processes that ATH1 and DELLAs regulate to change the growth habit, most of which remain unstudied.”

The study is published in the journal Proceedings of the National Academy of Sciences.

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By Chrissy Sexton, Earth.com Staff Writer