Broccoli going extinct? Scientists reveal why global warming turns it into cauliflower

ITHACA, N.Y. — A warming planet could mean the end of broccoli as we know it. Researchers from Cornell University explain that broccoli heads don’t develop properly when people try to grow them in higher temperatures. This leaves the plant looking more like cauliflower. Now, scientists finally have an answer as to why this happens — potentially opening the door to a way to save the crop.

Even the smallest amount of climate change has a particularly significant impact on broccoli. The vegetable grows best when people plant it in cooler temperatures in early spring or late summer into fall. Ideally, broccoli heads grow best when the average temperature is 61 degrees Fahrenheit. At 72 degrees (room temperature), the crown starts to deform. At 82 degrees, broccoli actually turns into a dense, cauliflower-like head — or a curd.

The problem is taking place in broccoli’s genes

Researchers experimented on broccoli by applying 5-azacytidine, a chemical which stops a process called DNA methylation. This is a process where a methyl group – a small molecule – is added to DNA. Methylation is one of the processes which turns genes on and off. In broccoli’s case, methylation shuts down a group of genes which broccoli needs to grow a healthy head.

When the team applied 5-azacytidine — shutting down DNA methylation — it allowed broccoli to grow normally even at temperatures over 80 degrees. Researchers say their results suggest that methylation is what is driving abnormal crop growth in warmer weather.

“Once we understand the mechanism better, we should be able to devise ways to develop a new biotechnology, a molecular genetics approach to suppress DNA methylation, in order to breed crops to grow in much warmer temperatures and in wider regions,” says co-corresponding author Susheng Gan, professor in the School of Integrative Plant Science Plant Biology Section, in the College of Agriculture and Life Sciences, in a university release.

Warming temperatures impact all aspects of plant growth

Study authors say flower development is extremely sensitive to temperature changes. Heat can reduce the quality and yield of vegetables like broccoli — where people eat the stems, stalks, leaves, and flowers. Gan adds their study adds evidence that DNA methylation may impact floral development in all crops, not just broccoli.

During their experiment, the team profiled broccoli plants (Brassica oleracea) using whole-genome sequencing. This helped to identify the plant’s methylome (where in the genes methylation is occurring) and its transcriptome (which genes are turning on).

Results show that sets of floral development cessation-associated genes (FCGs) help to regulate abnormal flower development. Genes that turn on FCGs shut down when the temperature rose above 72 and 82 degrees, respectively.

Without finding a way of counteracting these climate-related changes, global warming could regularly turn broccoli into a cauliflower-like curd.

The study is published in the journal Molecular Horticulture.

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