A plant molecule produces heme

The symbiotic relationship between legumes and the bacteria that grow on their roots is critical to the plant's survival

To establish this symbiotic relationship, some legumes produce hundreds of peptides that help bacteria survive in the structure of rhizobia

"This is the first truly detailed molecular mechanism of the 700 peptides in this system," said Graham Walker, MIT American Cancer Society Research Professor of Biology, Howard Hughes Medical Institute Professor, and senior author of the study

The heme-sequestering peptide may have beneficial uses in the treatment of a variety of human diseases, the researchers said

"This study shows that basic research on plant-microbe interactions also has the potential to translate into therapeutic applications," said Siva Sankari, a research scientist at MIT and lead author of the study

iron control

For nearly 40 years, Walker's lab has been studying the symbiotic relationship between legumes and Rhizobium, a type of nitrogen-fixing bacteria

A few years ago, plant biologists discovered that Medicago truncatula produces about 700 peptides that contribute to the formation of these bacterioids

The researchers then found that when they fused NCR247 to a larger protein, the hybrid protein was unexpectedly red in color

"Usually bacteria fine-tune their iron metabolism, and when there's enough iron, they don't take in more iron," Sankari said.

Nitrogenase, the main enzyme bacteria use to fix nitrogen, requires 24 to 32 iron atoms per enzyme molecule, so the extra influx of iron ions may help these enzymes become more active, the researchers said

"These peptides are produced in waves in the nodules, and when the bacteria are ready to fix nitrogen, the production of this particular peptide is higher

Without the NCR247 peptide, alfalfa and rhizobia could not form an effective nitrogen-fixing symbiosis, the researchers said

The peptides the researchers studied in this work could have potential therapeutic uses

A variety of human diseases cause free heme to circulate in the blood, including sickle cell anemia, sepsis, and malaria

The human protein hemagglutinin, which also binds to heme, is currently being explored as a possible treatment for sickle cell anemia