Functional and molecular characterization of SR45, a plant-specific factor involved in sugar and stress signaling in Arabidopsis thaliana

Dissertation presented to obtain the Ph.D degree in Molecular Biology

The process by which introns are removed from the precursor mRNA (pre-mRNA) is called RNA splicing. Multiple forms of mature mRNAs can be generated from a single pre-mRNA via a mechanism termed alternative splicing, which allows more than one polypeptide product to arise from a single gene and therefore largely contributes to generating transcriptome and proteome diversity. As sessile organisms, plants have evolved unique developmental and physiological strategies that allow them to adapt to an environment that is in constant change. Alternative splicing provides a quick and adjustable means of gene expression regulation, which is likely to be important in plant adaptive processes. The number of reported examples of alternative splicing in plants has increased exponentially over the past few years, and there is growing evidence that this posttranscriptional regulation mechanism plays a pivotal role in plant responses to environmental stress. Serine/arginine-rich (SR) proteins constitute a highly conserved family of splicing factors that play key roles in the early steps of spliceosome assembly. These RNAbinding proteins influence splice site selection in a concentration-dependent manner and are known to be key players in mammalian alternative splicing. At least 18 genes encoding SR proteins are present in the Arabidopsis thaliana genome. The SR45 splicing factor, which had been regarded as a classical SR protein, now falls outside the recently revised SR protein definition.

Financial support from Fundação para a Ciência e a Tecnologia, Portugal through grant SFRH/BD/27948/2006