New Relationship Between Gene Duplication and Alternative Splicing in Plants

Researchers from the University of Georgia, looking at how the isochorismate synthase (ICS) gene is regulated in Arabidopsis and Populus, found for the first time an inverse relationship between gene duplication and alternative splicing in plants. Led by Chung-Jui Tsai, the team believes that the discovery has implications for diversity not only in plants, but in animals and humans.

ICS encodes an enzyme that plays important roles in the synthesis of vitamin K for photosynthesis and synthesis of salicylic acid for stress response. Arabidopsis has two copies of the ICS gene. Populus, on the other hand, only has one. Tsai and colleagues discovered that Populus ICS undergoes extensive alternative splicing which is rare for the duplicated ICS and that it does not respond to stresses. Alternative splicing allows genes to produce two or more protein products with potentially different functions.

When the Populus ICS gene was inserted into an Arabidopsis mutant that lacked the stress-fighting ICS copy, the team found that the introduced gene could not be correctly spliced at all in the foreign Arabidopsis host and could not restore the plant's ability to produce salicylic acid. Tsai's team proved that unlike in Arabidopsis, Populus ICS functions primarily for photosynthesis. Populus, and other trees, which face environmental stress throughout their long lifetimes have evolved other pathways to synthesize salicylic acid and other chemicals for "constitutive" defense, Tsai pointed out.

"The finding that the Populus ICS gene cannot be properly spliced in Arabidopsis opens up new prospects in the quest for what makes a tree a tree," said Tsai. "The quest is certainly beyond differences in gene numbers, or individual gene functions, between trees and weeds."Tsai said she suspects that "subtle but fundamental differences in how genes are spliced between these species can have significant contributions as well."

Read the original story at http://www.uga.edu/news/artman/publish/printer_091207_Plants.shtml The open access paper published by PNAS is available at http://dx.doi.org/10.1073/pnas.0906869106