Pinoy biologists challenge idea of plant life

MANILA, Philippines – Can a plant exist without the genome that allows it to perform the basic function of photosynthesis? A plant that lives in the forests of Luzon apparently can, a study revealed.

Chloroplasts, a type of plastid or plant organelle, are at the core of plant life – it is essential in photosynthesis, is responsible for the green color of leaves, and provides many essential compounds the plant needs to live.

These chloroplasts are governed by a genome that gives these instructions, and even if a plant species, such as parasitic plants, ceases to do these, it has been thought that the genetic material remains.

However, two studies – one conducted by a team led by two Filipino biologists – found out that two organisms that should have the chloroplast genome could be missing it entirely, and one of the plants in question is native to the Philippines.

The Rafflesia lagascae is a parasitic plant species found in Luzon, and is best known for its huge, five-petaled flower that smells akin to rotting flesh. A team of scientists from the United States, Philippines, United Arab Emirates and New Zealand, led by Jeanmarie Molina of Long Island University and Michael Purugganan of New York University, showed that this particular Rafflesia species may be missing the genetic code in the chloroplast.

The Rafflesia is a parasitic plant, which means it doesn’t have to do photosynthesis for itself – its host plant does the hard work. Following the logic all plants, regardless of how they live, still have the chloroplast gene, the Rafflesia should still have it so it can still do other essential chemical processes. But Molina, Purugganan, and their team discovered that this particular plant species apparently doesn’t have an intact chloroplast genome.

“Using genome sequencing techniques, the researchers could not find an intact genome of the chloroplast in the parasitic plant Rafflesia lagascae. This is the first time that it has been shown that a plant can exist without a chloroplast genome,” the researchers said. 

They were only able to find small fragments of what used to be the chloroplast genome – and many of the genes apparently came from the Rafflesia‘s host, the vine species Tetrastigma.

One theory is that the genes have either relocated to the nucleus or the mitochondria of the plant, they said. In addition, despite the apparent absence of the chloroplast genome, the Rafflesia‘s cells still have structures that look like plastids – cell parts related to chloroplasts but do other plant functions.

Ideas about plants challenged

Meanwhile, another study, this time by a team of Canadian scientists, focused on the algal genus Polytomella, a single-cell plant that gets food from its water habitat.

Researchers David Roy Smith and Robert W Lee, in their study, tried to look for the plastid genome in four species of Polytomella – and they were not able to find one. Instead, they found proteins used in plastids, but none involved in expressing the plastid genes.

In effect, these two studies are challenging some of the the basic ideas of plant life.

The Rafflesia study, the researchers said “raises questions on how important plant compounds are chemically synthesized in plants,” and could have implications in pharmaceutical research.

Meanwhile, Smith tells The Scientist that both studies show plastids can lose genomes given a certain condition, “which opens up the big question: Why do they have genomes at all?”

Both studies were published online in February 2014. – Rappler.com

Full text

J. Molina et al., “Possible loss of the chloroplast genome in the parasitic flowering plant Rafflesia lagascae (Rafflesiaceae),” Molecular Biology and Evolution, doi:10.1093/molbev/msu051, 2014.

D. R. Smith and R. W. Lee, “A plastid without a genome: evidence from the nonphotosynthetic green alga Polytomella,” Plant Physiology, doi:10.1104/pp.113.233718, 2014.