Plant DNA recombinases: a long way to go

Abstract

DNA homologous recombination is fundamental process by which two homologous DNA molecules exchange the genetic information for the generation of genetic diversity and maintain the genomic integrity. DNA recombinases, a special group of proteins bind to single stranded DNA (ssDNA) nonspecifically and search the double stranded DNA (dsDNA) molecule for a stretch of DNA that is homologous with the bound ssDNA. Recombinase A (RecA) has been well characterized at genetic, biochemical, as well as structural level from prokaryotes. Two homologues of RecA called Rad51 and Dmc1 have been detected in yeast and higher eukaryotes and are known to mediate the homologous recombination in eukaryotes. The biochemistry and mechanism of action of recombinase is important in understanding the process of homologous recombination. Even though considerable progress has been made in yeast and human recombinases, understanding of the plant recombination and recombinases is at nascent stage. Since crop plants are subjected to different breeding techniques, it is important to know the homologous recombination process. This paper focuses on the properties of eukaryotes recombinases and recent developments in the field of plant recombinases Dmc1 and Rad51.

Figure 1

DNA damage caused by different genotoxic agents. The figure shows the formation of double strand breaks (DSBs) in dsDNA when exposed to DNA damaging agents like genotoxic chemicals, ionizing radiation as well as errors in the replication, programmed and unprogrammed action of nucleases.

Figure 2

Biochemical steps and corresponding proteins involved in homologous recombination in eukaryotes. Left hand side of the figure shows the different steps involved in the process and the corresponding proteins responsible for the process are shown on the right. The double strand break introduced in one of the two homologous DNA molecules is subjected to nucleolytic processing by MRX/MRN complex to expose 3′ ends. With the help of RPA, Rad52, Rad54, Rad55, Rad57, and Rad51/Dmc1, the ssDNA locates the complementary region on homologous DNA molecule resulting in strand invasion followed by strand exchange. Rad54 helps in branch migration. The 3′ ends are used as primers for new DNA synthesis at gap site. Resulted Holliday junction is resolved to generate repaired molecules.