Growing up with a sweet tooth: investigating the underlying mechanism of how sugars control miR156 levels in Arabidopsis

Abstract

Flowering in plants can only occur after juvenile plants have moved into an adult phase. This process has been described as early as 1790, and has later been phrased vegetative phase change. MicroRNA 156 has emerged as the regulator of vegetative phase change by repressing the positive regulator of flowering SPL. Interestingly, it has been shown that miR156 levels are strongly correlated to internal sugar levels, and correlated with the timing of phase change, offering a endogenous mechanism for the timing of vegetative phase change. These authors showed that sugar influences miR156 abundance at three levels: by reducing transcription of miR156 genes, by degrading pri-miR156 and by reducing mature miR156. Furthermore they found that sugar-induced miR156 reduction is partly dependent on the activity of the sugar sensor HEXOKINASE1. HXK1 is a major component of sugar-signalling pathways and this linked the sugar-induced miR156 reduction to sugar signalling. However it remains unclear which parts of the sugar signalling are involved in the sugar-induced miR156 reduction and how sugar is able to control miR156 abundance transcriptionally and post-transcriptionally. We will test this in a two way approach. Firstly, we will investigate which parts of sugar-signalling are involved in the sugar-induced miR156 reduction. Furthermore, to find involved mechanisms unrelated to sugar signalling, a mutagenesis screen will be performed. Secondly, we will investigate how sugar controls miR156 reduction by investigating how sugar represses transcription, how it leads to degradation of pri-miR156 and how it is able to reduce mature miR156 levels. Positive results of the first part will supplement the research of the second part.