Biological complexity: how plants stop U_V damage (Introduction)

by David Turell @, Tuesday, April 17, 2018, 18:53 (339 days ago) @ David Turell

Plants sit out in the sun, needing it for energy , but are exposed to UV radiation, and must protect themselves. They have a mechanism like animals have with slight different proteins employed:

"because plants can't come in from the sun or slather on sunblock, they have a super robust DNA repair kit. Today, the UNC School of Medicine lab of 2015 Nobel laureate Aziz Sancar, MD, PhD, has published an exquisite study of this powerful DNA repair system in plants, which closely resembles a repair system found in humans and other animals.

"The study, published in Nature Communications, is the first repair map of an entire multicellular organism. It revealed that the "nucleotide excision repair" system works much more efficiently in the active genes of plants as compared to humans. And this efficiency depends on the day/night cycle.


"Sancar, the Sarah Graham Kenan Professor of Biochemistry and Biophysics, was awarded the 2015 Nobel Prize in Chemistry for his studies of excision repair, which is now widely viewed as the major mechanism of DNA repair -- including repair of UV damage -- in living organisms.


"For the study, Oztas and colleagues used an excision-repair mapping technique they recently developed, known as XR-seq. The technique enables them to detect and sequence the short lengths of damaged DNA that are cut from chromosomes during the excision repair process. The sequences of these DNA snippets can be matched to corresponding stretches of DNA on a reference genome, in order to map precisely the spots where DNA-damage is under repair.

"The UNC researchers performed XR-seq scans on cells from UV-exposed plants -- Arabidopsis thaliana, the "lab rat" of plant research also known as thale cress or mouse-ear cress. The resulting repair maps revealed that excision repair in Arabidopsis works faster on genes that are active. Genes when active are transcribed into strands of RNA that may then be translated into proteins, the main machinery of cells. Prior studies from the Sancar lab showed that excision repair works more efficiently for actively transcribed genes in animals and bacteria. The phenomenon, called transcription-coupled repair, is thought to have evolved as a way to direct DNA repair where it is most acutely needed.

"'Here we found that the jump in efficiency for transcription-coupled repair is even more pronounced in plants than it is in animals or bacteria," Oztas said.

"Sancar's lab performed XR-seq on UV-exposed Arabidopsis over 24-hour periods to discover that the efficiency of transcription-coupled repair also varies according to the "circadian" day/night cycle for 10 to 30 percent of Arabidopsis's genes. This reflects the normal daily variations of transcription activity in these genes.

"'The results show that excision repair in plants is regulated in much the same way it is in other organisms -- in order to maximize efficiency," Oztas said.


"The plant excision repair system also involves a slightly different set of repair proteins than are found in other organisms. The UNC scientists hope to determine why that is and precisely how plants' distinctive set of excision repair proteins work together to keep plant genomes in good repair."

Comment: Since plants must be constantly exposed to sunlight and UV wavelengths, this system must have been designed into plants at the beginning of plants development on Earth. Not by chance.

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