Previous studies hypothesized that extreme branching might be the result of a pause or a delay in the maturation of inflorescence meristems, causing them to sprout extra branches instead of ending their growth by making flowers. "Our previous work as well as those of others hinted at the existence of a timer or clock," Lippman notes. "We wanted to define this clock at the highest resolution, in terms of the genes that modulate the rate of meristem maturation, with the idea that finding the genes that define the clock would enable us to tweak it to get the desired level of branching."
Using a systems biology approach and next-generation sequencing technology to "capture" the transcriptome the activity of all the genes in a genome of stem cells at five different stages of maturation, the team identified nearly 4000 genes that represent the clock. With help from CSHL associate professor and computational biologist Michael Schatz, the team, which included post-doctoral researchers Soon-ju Park and Ke Jiang, compared the clocks of a mutant variety that undergoes extreme branching and a wild relative from Peru that undergoes modest branching.
This analysis revealed that subtle differences in the activity of the clock's genes could alter branching architecture. "Our data showed that wild relatives of tomato have evolved to have a slight delay in maturation, which leads to just a few more branches and a doubling of the number of flowers and fruits compared to what is typically found on cultivated tomatoes grown for ketchup or in the home garden," explains Lippman, who is enthusiastic about the implications of this work and the next steps that his team will take. "We now have a master list of candidate genes that we can go after to manipulate the clock in order to make domesticated tomatoes produce a branching architecture that's similar to the wild variety," he say
|Contact: Hema Bashyam|
Cold Spring Harbor Laboratory