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

Short Answer: Polycomb gene family controls the expression of MADSbox and homeobox gene families (found in Arabidopsis and Drosophila, respectively) by targeting and modifying chromatin features associated with these homeotic genes, such as histone modifications and chromatin accessibility. This mechanism operates irrespective of the DNA-binding domain differences between MADSbox and homeobox genes, allowing Polycomb genes to regulate their expression and coordinate developmental processes in both plants and animals.

Step-by-step solution

Understanding Homeotic Genes

Homeotic genes are involved in determining the overall body pattern and the formation of structures during development. These genes are responsible for organizing the identity of different body segments in both plants and animals.

Differences between MADSbox and Homeobox Gene Families

MADSbox and homeobox gene families are two different families of homeotic genes. MADSbox gene family, found mostly in plants like Arabidopsis, consists of genes that code for a specific DNA-binding domain called the MADS domain. On the other hand, homeobox gene family, found in animals like Drosophila, consists of genes that code for a similar DNA-binding domain called the homeodomain.

Role of Polycomb Gene Family in Gene Expression

Polycomb group (PcG) genes are a set of conserved genes that are responsible for controlling the expression of homeotic genes by modifying the chromatin structure. PcG proteins are known to form complexes that can specifically bind to chromatin, altering its structure, and thereby, repress target gene expression. Polycomb gene family operates based on epigenetic regulation to maintain the desired pattern of gene expression.

Answering the Main Question

Despite the differences in the DNA-binding domains of MADSbox and homeobox gene families, Polycomb gene family can control their expression because it doesn't rely on the sequence-specific DNA-binding domains. Instead, Polycomb proteins target specific chromatin features associated with these homeotic genes, such as histone modifications and chromatin accessibility. By targeting and modifying these chromatin features, Polycomb proteins can inhibit or promote the expression of both MADSbox and homeobox homeotic genes, regardless of their DNA-binding domain differences. This allows Polycomb genes to control the expression of two very different sets of homeotic genes in Arabidopsis and Drosophila.