Genetic regulation of maize floral development - insights from the transcriptome and translatome

Abstract

Flowers are produced by floral meristems, groups of stem cells that give rise to floral organs. In grasses, including the major cereal crops, flowers (florets) are contained in spikelets, which contain one to many florets, depending on the species. Floral development in plants is regulated by gene expression. Understanding gene expression regulation in maize floral development is critical to regulate floret fertility in other grasses and potentially useful to engineer more productive cereal crops. In this work, I focus on gene expression regulation at transcriptome and translatome level to gain insights into floral development. To transcriptionally gain insight into the functional differences between florets with different fates, I examined gene expression in upper and lower floral meristems in maize ear using laser capture microdissection coupled with RNA sequencing. Differentially expressed genes were involved in hormone regulation, cell wall, sugar and energy homeostasis. Furthermore, cell wall modifications and sugar accumulation differed between the upper and lower florets. Finally, a novel boundary domain between upper and lower florets was identified, which might be important for floral meristem activity. A model is proposed, in which growth is suppressed in the lower floret by limiting sugar availability and upregulating genes involved in growth repression. To gain insight into microRNA regulation in maize floral development, I examined the translatome of a maize microRNA biogenesis mutant and normal siblings using ribosome profiling and RNA sequencing. My results indicated microRNAs in maize regulate both mRNA decay and translation repression. Importantly, translation repression by microRNAs is broad but magnitude is small in maize. Furthermore, translation is broadly affected beyond direct microRNA targets when microRNAs are perturbed. Thus, translation regulation is likely a critical regulator gene expression during floral development.