Alternative Splicing in Plants: Retain or Remove?

Shih et al. investigate red light-triggered pre-mRNA splicing in Physcomitrella patens. Plant Cell (2019) 

 By Chueh-Ju Shih and Shih-Long Tu

 Background: Light is important for plant growth and development. Plants have developed various types of photoreceptors to perceive different wavelength of lights. In response to light, photoreceptors tightly regulate gene expression at various levels. Alternative splicing (AS) is a widespread mechanism in eukaryotes that generates two or more mRNAs from the same pre-mRNA, therefore potentially leading to the generation of multiple protein products or unstable mRNAs. AS is tightly controlled by splicing regulators, which recruit spliceosomal components to initiate splicing. Several studies have suggested that the red/far-red light photoreceptor phytochrome participates in light-mediated splicing regulation, but the detailed mechanism remains unclear.

Question: We aim to understand how phytochromes regulate AS. Do phytochromes interact with the splicing machinery? Does such regulation affect plant growth and development?

Findings: In the moss Physcomitrella patens, when phytochrome is activated by light, it interacts with the splicing regulator PphnRNP-H1. PphnRNP-H1 binds with higher affinity to the spliceosomal component PpPRP39-1 in the presence of light-activated phytochromes. Such an interaction might induce the dissociation PpPRP39-1 from the spliceosome. PpPHY4, PphnRNP-H1, and PpPRP39-1 are all involved in light-mediated splicing regulation. Our results suggest that phytochromes target the early step of spliceosome assembly via a cascade of protein–protein interactions to control pre-mRNA splicing and photomorphogenic responses.

Next steps: PphnRNP-H1 might associate with pre-mRNA, as it contains an RNA recognition domain. We plan to investigate the target transcripts of hnRNP-H1 in response to light. How phytochromes modulate hnRNP-H1 activity is also an important question to investigate.

 Chueh-Ju Shih, Hsiang-Wen Chen, Hsin-Yu Hsieh, Yung-Hua Lai, Fang-Yi Chiu, Yu-Rong Chen, and Shih-Long Tu (2019). Heterogeneous Nuclear Ribonucleoprotein H1 Coordinates with Phytochrome and the U1 snRNP Complex to Regulate Alternative Splicing in Physcomitrella patens. Plant Cell 31: xxx.

Key words: Phytochrome, alternative splicing, splicing regulator