Question

The floral homeotic genes of Arabidopsis belong to the MADSbox gene family, while in Drosophila, homeotic genes belong to the homeobox gene family. In both Arabidopsis and Drosophila, members of the Polycomb gene family control expression of these divergent homeotic genes. How do Polycomb genes control expression of two very different sets of homeotic genes?

Short answer

Polycomb genes control the expression of two different sets of homeotic genes, MADS-box genes in Arabidopsis and homeobox genes in Drosophila, through their epigenetic regulatory mechanisms. They produce proteins that form Polycomb repressive complexes (PRCs), which modify the chromatin structure and affect gene expression. PRCs can either activate or repress transcription of target genes depending on their modifications on the chromatin, such as methylation or acetylation. Regardless of the type of homeotic gene, Polycomb genes act by controlling chromatin structure, which is a central regulatory element in both Arabidopsis and Drosophila.

Step-by-step solution

Understand homeotic genes, MADS-box, homeobox, and Polycomb gene families

Homeotic genes are responsible for determining the basic body plan and development of an organism, ensuring that body parts develop in the correct position and sequence. MADS-box genes are a subset of homeotic genes found in Arabidopsis that encode transcription factors, which control the development of plant reproductive organs. Homeobox genes are a subset of homeotic genes found in Drosophila and many other organisms, and they also encode transcription factors controlling body plan and segment development. Polycomb gene family is a group of genes that act as epigenetic regulators of gene expression, meaning they control expression of other genes by modifying chromatin structures without changing the DNA sequence itself.

The role of Polycomb genes in controlling gene expression

Polycomb genes produce proteins that can form complexes called Polycomb repressive complexes (PRCs). These complexes can modify the chromatin structure and as a result, affect gene expression. PRCs can either activate or repress transcription of target genes depending on their modifications on the chromatin, such as methylation or acetylation.

Polycomb genes' mechanism of action on both Arabidopsis and Drosophila homeotic genes

Although MADS-box gene family in Arabidopsis and homeobox gene family in Drosophila are different sets of homeotic genes, both types of genes are controlled by the epigenetic regulation mechanisms involving Polycomb repressive complexes. PRCs recognize specific DNA sequences in the regulatory regions of target genes and modify the chromatin structure by adding or removing chemical groups. These groups can influence the accessibility of the DNA to other proteins involved in transcription, therefore controlling the expression levels of target homeotic genes. In summary, Polycomb genes can control the expression of two very different sets of homeotic genes (MADS-box and homeobox families), because their mechanism of action is focused on the regulation of chromatin structure, which plays a central role in gene expression control in both Arabidopsis and Drosophila.