Plant Agc protein kinases orient auxin-mediated differential growth and organogenesis

Abstract

In view of their predominant sessile lifestyle, plants need to be able to adapt to changes in their environment. Environmental signals such as light and gravity modulate plant growth and architecture by redirecting polar cell-to-cell transport of auxin, thus causing changes in the distribution of this plant hormone. The PIN auxin efflux carriers are key drivers of auxin transport that determine the direction of auxin flow through their asymmetric subcellular distribution. An important component in PIN polarity establishment is the plant protein kinase PINOID (PID). PID instructs apical (shoot meristem facing) PIN polarity by phosphorylating the central hydrophylic loop of PIN proteins (PINHL). In this thesis we investigated modulation of PID activity by the calcium binding proteins TCH3 and PBP1, and by the protein kinase PDK1. All three proteins were found to regulate both the enzymatic activity and the sub-cellular localisation of PID in response to calcium and phospholipids, respectively, and as such they are likely to be involved in translating environmental signals into PIN polarity changes. In addition, we show that PID and its close homologs act both redundantly and differentially in orienting plant development by instructing the subcellular distribution of PINs.