Fusion of the SRDX motif to OsPIL11 or OsPIL16 causes rice constitutively photomorphogenic phenotypes in darkness

Dark-grown seedlings develop skotomorphogenesis. Because of the development of rice direct seeding cultivation systems, there is an increasing need for clarifying the molecular mechanism underlying rice skotomorphogenic development. It has been reported that SRDX motif, LDLDLELRLGFA, was able to convert a transcriptional activator into a strong repressor. In the present study, to explore the functions of PILs in rice skotomorphogenesis, we generated OsPIL11-SRDX and OsPIL16-SRDX transgenic lines by fusing the SRDX transcriptional repressor motif to the C-terminal of two members of the phytochrome interacting factor-like (OsPIL) family in rice (OsPIL11 and OsPIL16). The OsPIL11-SRDX and OsPIL16-SRDX seedlings grown in darkness had constitutively photomorphogenic phenotypes with short coleoptiles and open leaf blades. The results of an RNA sequencing analysis revealed that the dark-grown OsPIL11-SRDX and OsPIL16-SRDX lines had gene expression patterns similar to those of wild-type seedlings grown under red light. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses indicated that the expression levels of genes related to photosynthesis, photosynthesis–antenna proteins, and porphyrin and chlorophyll metabolism were up-regulated in the dark-grown OsPIL11-SRDX and OsPIL16-SRDX lines, whereas the expression of genes related to the auxin pathway was down-regulated. In contrast, the expression levels of these photosynthesis-related genes were down-regulated in dark-grown transgenic seedlings overexpressing OsPIL11 or OsPIL16, which had exaggerated skotomorphogenesis. Considered together, our data indicate that OsPIL11 and OsPIL16 primarily function as transcriptional activators, at least in regards to promoting skotomorphogenesis and repressing the expression of photosynthesis-related genes.