ENVIRONMENTAL EPIGENETICS IN MAIZE: ADVANCES FROM A EUROPEAN INITIATIVE

The AENEAS (Acquired Environmental Epigenetics Advances: from Arabidopsis to maize) research collaborative project was recently funded by the European Commission. The AENEAS initiative aims to assess the impact of environmental conditions on epigenetic states in the model plant Arabidopsis thaliana and then transfer knowledge to maize: one of the most important crops of the world. Here, we illustrate some of the recent advances obtained by studying maize epigenetics within AENEAS project.A first objective of AENEAS is to characterize, in maize, three epi-regulatory pathways, which have been chosen because they are well characterized in Arabidopsis for their interaction with environmental signals in mediating changes into the epigenome. These pathways are: the autonomous flowering (AF), the CpG methylation (mCG), and the small RNA (sRNA) pathway. The expected outcome is to produce tools (e.g. mutants and epi-targets) to be subsequently employed to analyze epigenetic-mediated response to environmental cues. In this context, we have focused our study on the maize homolog (named nfc102) of the Arabidopsis FVE gene, which encodes a MSI-like WD-repeat protein belonging to AF pathway. Phenotypic analysis of nfc102 RNAi mutants revealed that plants exhibit several developmental defects, suggesting a pleiotropic nfc102 function. Among sequences showing differences in RNA accumulation in nfc102 mutant compared to wild-type plants is enclosed the maize homolog of the Arabidopsis florigen FT (ZCN8). Our results suggest that nfc102 is involved in regulating processing of ZCN8 sense and antisense RNA. Additional targets of nfc102 function are different types of transposons and retrotransposons (TEs), which show an increase of their RNA level in nfc102 mutants. In accordance with a nfc102 role in epigenetic-mediated silencing, a decrease of histone marks associated with transcription activation and an increase of histone modifications related to silencing was also observed in the TEs analyzed. Finally, we show that nfc102 gene is ubiquitously expressed, but it exhibits a specific accumulation of sense and antisense RNA in specific tissues, including inflorescences.Since nfc102 regulates the RNA level of various TEs and because it is well known that TEs are sensitive to different environmental cues, we have performed experiments to analyze TEs response in nfc102 mutants, concomitantly with application of temperature stresses. In these experiments we have also enclosed the rmr6 mutant, affecting the function of the maize homolog of the Arabidopsis NRPD1 gene, which encodes the largest subunit of RNA polymerase IV. Since retrotransposition occurs through retrotranscription of TE-derived RNAs, the level of both transcripts and extrachromosomal DNA copies for a number of TEs was detected. The analysis was performed immediately after stress removal and after some days of recovery to assess maintenance of changes through mitotic division. Preliminary results from these experiments will be illustrated and discussed.