GSE112662
Genomic evidence reveals SPA-regulated developmental and metabolic pathways in dark-grown Arabidopsis seedlings
Background: Photomorphogenesis is repressed in the dark mainly by an E3 ubiquitin ligase complex comprising CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) and four homologous proteins called SUPPRESSOR OF PHYA-105 (SPA1-SPA4) in Arabidopsis. This complex induces the ubiquitination and subsequent degradation of positively acting transcription factors (e.g., HY5, HFR1, PAP1 and others) in the dark to repress photomorphogenesis. Genomic evidence showed a large number of genes regulated by COP1 in the dark, of which many are direct targets of HY5. However, the genomic bases for the constitutive photomorphogenic phenotypes of spaQ remain unknown. Results: Here, we show that >7200 genes are differentially expressed in the spaQ background compared to wild type in the dark. Comparison of the RNAseq data between cop1 and spaQ revealed a large overlapping set of genes regulated by the COP1-SPA complex. In addition, many of the genes coordinately regulated by the COP1-SPA complex are also regulated by HY5 directly and indirectly. Moreover, a large number of genes (~2790) are predominantly regulated by SPA proteins and not by COP1, suggesting that SPA proteins might regulate many biological processes independently of COP1. Conclusions: Taken together, our data reveal that SPA proteins repress photomorphogenesis by controlling expression of a large number of genes in concert with COP1, likely through regulating the abundance of downstream transcription factors in light signaling pathways. Moreover, SPA proteins may function both in a COP1-dependent and –independent manner in regulating many biological processes and developmental pathways in Arabidopsis. Overall design: Total of 9 samples of  3 day dark-grown seedlings,  wild-type, cop1-4 mutant and spaQ mutant, each has three replicates