Plant responses to full moonlight requires the SUVH4 HMTase which may target active genes via interaction with the splicing factor SAP18

The relationships between plants and the moonlight is frequently dismissed as a myth, which obstructs a deeper understanding of this topic, but recent work provided evidence for its effect on plant cellular activities and growth. We addressed the involvement of the Arabidopsis epigenetic modifiers DDM1 and SUVH4 in plant responses to full moonlight (FML) by using their corresponding mutants. Wild type (WT) and ddm1 etiolated seedlings responded to FML by apical hook opening and cotyledon unfolding; suvh4 mutant was impaired in skotomorphogenesis. Exposure to FML resulted in notable changes in genome organization and protein and metabolite profiles in WT and ddm1 but not in suvh4. Among the upregulated proteins in WT and ddm1 are those related to photosynthesis such as the photosystem I reaction center subunits PSAK and PSAH1 and chlorophyll a-b binding proteins LHB1B1 and LHCA1 as well as the blue light receptor phototropin 1 (PHOT1) and the phytochrome-associated serine/thronine-protein phosphatase 1 (PYPP1). Using GST pull down coupled proteome analysis we identified the apoptosis and splicing-associated protein (ASAP) SAP18 as a SUVH4 interacting protein. The interaction of SUVH4 with SAP18 was confirmed by GFP-TRAP of proteins extracted from SAP18-GFP expressing plants followed by proteome analysis. Indeed, SAP18-GFP could trap SUVH4 along with SR45 and the Acinus paralog PININ, components of the ASAP complex. Our study highlighted a previously unrecognized link between histone modification by SUVH4 HMTase and the ASAP complex of splicing factors which may facilitate the silencing of active genes and possibly interpret the moonlight signal into a functional state.