Plants face the constant challenge of accurately passing down their genetic information to future generations. In this blog post, we explore how Arabidopsis thaliana, a common model plant, has evolved a remarkable backup system to ensure the precise partitioning of chromosomes during cell division. Discover the intricate mechanisms plants employ to maintain genetic stability and adapt to environmental changes.
River VIPLThe Delicate Dance of Chromosome Segregation
Consider the complexity of the way that plants reproduce to share their genetic material correctly. A plant, however, must carefully partition billions of chromosomes to each cell division. This is a delicate process which can be thrown out of balance in any number of ways which in turn stops the plant living or reproducing.
To address this challenge, plants like Arabidopsis thaliana have evolved an elegant alternative. This system rests upon a backbone molecule known as DDM1, which is vital for chromosome separation when cells divide. Every time a cell divides, chromosomes must be correctly partitioned. This requires a centromere on each chromosome and in plants, centromeres regulate the partitioning of chromosomes with the assistance of DDM1.
Seeing Arabidopsis at Its Heartless Best
In fact, when their human version of DDM1 is lost, it’s responsible for a devastating genetic disorder, called ICF syndrome, in which centromeres can no longer be divided equitably. If DDM1 is lost in Arabidopsis, however, the plant thrives. Martienssen was so struck by this that he and his group, who included Tetsuji Kakutani, decided to take a deeper look.
They found that in addition to CRISP-Cas, plants have a second backup system called RNA interference (RNAi). “Plants really have both DDM1 and RNAi,” Martienssen notes. So we said, ‘Well let’s knock these two down in Arabidopsis’. And we did that, and it turns out the plants just looked really bad. Closer inspection revealed only a single transposon—the genetic element from the unlinked chromosome 5—was responsible for the phenotypes observed.
Small RNAs to the Rescue: Reviving Centromere Function
They reecntly found that in Arabidopsis, DDM1 and RNAi cooperate to protect centromere function and Hedgehog division. If both systems go awry, the parasitic centromere on chromosome 5 creates a great deal of trouble. But Martienssen and lead author, Atsushi Shimada, found a way around this.
The authors designed short hairpin RNAs against the troublesome transposon. These little RNAs compensate for the absence of DDM1. They found that all the transposon copies in the centromere were recognized and, incredibly, they regenerated a functional centromere. And now the plants were reproductive. They make seeds. They are much improved,” says Martienssen.
Besides explaining how plants use the process to maintain genetic integrity, this discovery is expected to be relevant to human health applications. Thus, skewed centromere division can contribute to diseases such as ICF syndrome and early cancer progression. Perhaps one day, the research from Martienssen’s team could be part of a new generation of treatments for AD and some other human diseases.
