Emerging Functions of Plant Serine/Arginine-Rich (SR) Proteins: Lessons from Animals

Serine/arginine-rich (SR) proteins are widely found in higher eukaryotes, including metazoans and plants. They form a major family of essential splicing factors that function in both constitutive splicing (CS) and alternative splicing (AS). Some SR proteins can also shuttle between the nucleus and cytoplasm and have roles beyond splicing. The activities of SR proteins are required for many living organisms to maintain normal growth and development. Although SR genes have been identified in numerous plants, they are less studied than those found in animals. The results of existing research suggest that plant SR proteins share many similar properties with their animal counterparts. However, plants generally have a higher number of SR proteins that display largely redundant functions under normal conditions but participate in specific stress responses. Moreover, many animal and plant SR genes are alternatively spliced and can be regulated by themselves or other SR proteins. These AS events, often coupled to nonsense-mediated decay (NMD), enable a mechanism for protein amount control under different conditions but sometimes also lead to translated protein isoforms with different functions. Here, we summarize the key findings of SR proteins in animals and plants and compare the essential characteristics of SR studies in these two research areas.