Auxin effects on maize seed transciptome during the early stages of endosperm development

In angiosperms, the endosperm is the primary nourishing tissue that provides nutrients for seed germination and in monocots it represents the main constituent of the seed. Cereal seed, and in particular maize seed, could be used as a model for the study of the endosperm tissue. To discover the genes involved in early seed development we performed a time course experiment of the transcriptome of the maize endosperm at 8, 12 and 16 DAP. Endosperm transcript profiling was extended to a mutant impaired in auxin biosynthesis, defective endosperm 18 (de18), to study the hormone-dependent transcriptional network and in particular the auxin effect on transcriptome. The number of transcripts aligned to the reference genome progressively decreased from 8 to 16 DAP and the majority of them were up-regulated in the earliest stage. This evidences a more dynamic transcriptional regulation at 8 DAP, as expected for endosperm that is a tissue that undergoes cell death at maturation. Gene Ontology (GO) analysis of annotated genes showed that these genes were enriched in biological process terms such as cellular and metabolic processes, regulation of biological process, localization and response to stimulus. As regards the molecular function category, the most representative belong to the binding and catalytic activity terms. The main GO term found up regulated during development was the nutrient reservoir activity that is in agreement with the storage accumulation function of endosperm. The regulation of RNA metabolic process, transcription and signaling were the main GO terms down regulated together with the RNA transport, mRNA surveillance and biosynthesis of secondary metabolites pathways. DEGs belonging to hormones signaling pathways, cell cycle and epigenetic effectors were evidenced and validated by real time PCR and in situ hybridization. A morphological description of the mutant and wild type together with the in situ hybridization of the most interesting genes will allow localizing genes related to early endosperm development.