A plethora of plant serine/arginine-rich proteins: redundancy or evolution of novel gene functions?

Precursor-mRNA (pre-mRNA) processing is an important step in gene expression and its regulation leads to the expansion of the gene product repertoire. SR (serine-arginine)-rich proteins are key players in intron recognition and spliceosome assembly and significantly contribute to the alternative splicing process. Due to several duplication events, at least 19 SR proteins are present in the Arabidopsis genome, which is almost twice as many as in humans. They fall into seven different subfamilies, three of them homologous with metazoan splicing factors, whereas the other four seem to be specific for plants. The current results show that most of the duplicated genes have different spatiotemporal expression patterns indicating functional diversification. interestingly, most of the SIR protein genes are alternatively spliced and in some cases this process was shown to be under developmental and/or environmental control. This might greatly influence gene expression of target genes as also exemplified by ectopic expression studies of particular SR proteins.