The RS domain of Arabidopsis splicing factor RRC1 is required for phytochrome B signal transduction

Abstract

SUMMARYPlants monitor the light environment through informational photoreceptors that include phytochromes. In seedling de-etiolation, phytochrome B (phyB), which is the most important member of the phytochrome family, interacts with transcription factors to regulate gene expression and transduce light signals. In this study, we identified rrc1 (reduced red-light responses in cry1cry2 background 1), an Arabidopsis mutant that is impaired in phyB-mediated light responses. A genetic analysis demonstrated that RRC1 affected light signaling in a phyB-dependent manner. RRC1 encodes an ortholog of the human potential splicing factor SR140. The RRC1 polypeptide contains a C-terminal arginine/serine-rich (RS) domain that is important for the regulation of alternative splicing. Although the complete loss of RRC1 caused pleiotropic developmental abnormalities, the deletion of the RS domain specifically reduced phyB signaling and caused aberrant alternative splicing of several SR protein genes. Moreover, semi-quantitative RT-PCR analysis revealed that the alternative splicing patterns of some of the SR protein genes were altered in a red-light-dependent manner, and that these responses were reduced in both phyB and rrc1 mutants. These findings suggest that the regulation of alternative splicing by the RS domain of RRC1 plays an important role in phyB signal transduction.

Phytochrome controls alternative splicing to mediate light responses in Arabidopsis

“…Phytochrome probably regulates the expression level (mRNA and protein level) or posttranslational modification of more upstream splicing regulators. RRC1, an SR-like splicing factor that is required for phyB signaling, is among these candidate upstream factors, because the R-responsive AS alterations of RS31 an SR34b have been shown to be partially dependent on RRC1 (21). Moreover, we found that some of the early R-responsive and phytochrome-dependent AS changes were substantially reduced in rrc1 mutants, whereas others were totally independent of RRC1 (Fig.…”

“…Time-course analysis revealed that the AS changes were detected within 1 h and peaked 3 h after pR irradiation (Fig. S2E), as was the case for cR irradiation (21). Next, we exposed etiolated seedlings to various intensities of 2-min pR or 3-h cR to confirm that the AS responses were dependent on the fluence rate of R (Fig.…”

“…PhyA and PhyB Are Responsible for R-Dependent AS Control. We previously showed that two SR protein genes, RS31 and SR34b, display cR-induced changes in AS, and that this response is partially reduced in phyB mutants (21). The mRNAseq analysis conducted in this study revealed that RS31 and SR34b undergo phytochrome-mediated AS control (Dataset S1).…”

“…However, the physiological significance of this finding and the identity of the photoreceptors that mediate light-regulated AS remain unclear. Recently, we identified rrc1 (reduced red-light responses in cry1cry2 background 1), an Arabidopsis mutant that is impaired in phyB-mediated light responses (21). Because RRC1 encodes a novel SR-like protein and rrc1 mutants show aberrant AS profiles, we hypothesized that RRC1 controls AS to mediate phyB signaling.…”

“…Because RRC1 encodes a novel SR-like protein and rrc1 mutants show aberrant AS profiles, we hypothesized that RRC1 controls AS to mediate phyB signaling. Furthermore, we proposed that phyB is involved in the R-dependent AS changes of several genes (21).…”