Cell division plays a central role in plant development, since it supplies the plant body with new cells. In the eukaryotic cell cycle, two important events occur: the DNA duplication and segregation of the genetic material.
Control of the cell cycle is essential. It guarantees daughter cells will receive correctly duplicated DNA, and that it will occur no more than once at each cycle. Also, that cell division does not occur until duplication of the DNA is correct and complete.
The APC (Anaphase-promoting complex), composed of at least 11 subunits, is an essential multiproteic complex for the mitotic progression. It presents ubiquitin E3 ligase activity, tagging target proteins for ubiquitination and directing them to degradation via 26S proteasome.
Mining in the Arabidopsis thaliana genome led to the identification of an ORF with high homology to the APC7 subunit of the Anaphase-promoting complex. Surprisingly a C-terminal portion of 263 amino acids of this ORF shows high homology to a tobacco gene that codes for a protein with antiviral activity, called inhibitor of virus replication (IVR)-like. This protein greatly reduces the replication of the Tobacco mosaic virus (TMV) in assays with Nicotiana tabacum.
The AtAPC7 gene presents alternative processing of mRNA: the complete transcript AtAPC7 and another one which contains only the C-terminal region called AtAPC7 splicing. In order to study the possible distinct functions of these splicing products, the mRNA levels of the AtAPC7 variant forms were investigated through real time RT-PCR. In general, the AtAPC7 splicing show higher levels of mRNA than the AtAPC7 in Arabidopsis thaliana.  Moreover, the AtAPC7 splicing is highly expressed in reproductive organs, while AtAPC7 is more intensively expressed in vegetative organs. Mining at the TAIR microarray database (www.arabidopsis.org) confirmed the observations.
Aiming to investigate the possible distinct functions of the splicing variants during plant development, genetic transformation of Arabidopsis thaliana was carried out with the full-length AtAPC7 cDNA, the AtAPC7 3' end splicing variant and with a subclone containing only the 5' region AtAPC7 cDNA, under the control of the 35S constitutive promoter. Surprisingly, only plants transformed with the cDNA corresponding to the C-terminal region of the AtAPC7 protein grow quite faster than control. These plants are being further characterized.
This work was funded by CAPES.