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Once the energy resources in a seed are depleted, seedlings switch on a 'green' photosynthesis program. (Jesse Woodson/Salk Institute for Biological Studies)
Genes inside plant chloroplasts, the structures that house the photosynthetic pigment chlorophyll, help an embryonic plant to begin photosynthesizing, according to a study published in the May issue of the journal Current Biology.
Scientists in California at the Salk Institute for Biological Studies have revealed how these signals are relayed.
"When a seedling establishes a photosynthetic lifestyle, it needs to activate several thousand genes in the nucleus," said team leader Joanne Chory in a press release.
"One of the signals to do this comes from the organelle in charge of photosynthesis, called the chloroplast. In this study we identified this signaling molecule as heme."
Heme is a cofactor in multiple plant and animal biosynthetic pathways, being most notably the oxygen-bearing component of hemoglobin in red blood cells.
When plants encounter stressful situations, such as the herbicide norflurazon, the genes that control photosynthesis are turned off leading to a bleached appearance. (Jesse Woodson/Salk Institute for Biological Studies)
The researchers used the mustard plant Arabidopsis thaliana in their work because it grows easily and quickly, its genome has already been sequenced, and it can be manipulated genetically.
They found that a gene in genetically altered plants, called gun 6, synthesizes the enzyme ferrochelatase 1 (FC1), and plants with this gene make too much FC1, which is needed to synthesize heme. Excess heme may lead to expression of photosynthesis-related genes.
"Heme is likely the signal sent from a healthy chloroplast to the nucleus saying it is time to make proteins required for photosynthesis,” said co-author Jesse Woodson in the release.
These findings help to explain how a young plant grows, generates chloroplasts, and captures sunlight to become a photosynthetic organism.
"Understanding how plants coordinate gene expression between the chloroplast and nucleus will ultimately increase crop yields in the field, where plants often encounter multiple stresses during the growing season,” Chory said.
