Evolutionary Adaptations of Plant AGC Kinases: From Light Signaling to Cell Polarity Regulation.

Signaling and trafficking over membranes involves a plethora of transmembrane proteins that control the flow of compounds or relay specific signaling events. Next to external cues, internal stimuli can modify the activity or abundance of these proteins at the plasma membrane (PM). One such regulatory mechanism is protein phosphorylation by membrane-associated kinases, several of which are AGC kinases.

Different auxin response machineries control distinct cell fates in the early plant embryo.

The cell types of the plant root are first specified early during embryogenesis and are maintained throughout plant life. Auxin plays an essential role in embryonic root initiation, in part through the action of the ARF5/MP transcription factor and its auxin-labile inhibitor IAA12/BDL. MP and BDL function in embryonic cells but promote auxin transport to adjacent extraembryonic suspensor cells, including the quiescent center precursor (hypophysis).

A cellular expression map of the Arabidopsis AUXIN RESPONSE FACTOR gene family.

The plant hormone auxin triggers a wide range of developmental and growth responses throughout a plant's life. Most well-known auxin responses involve changes in gene expression that are mediated by a short pathway involving an auxin-receptor/ubiquitin-ligase, DNA-binding auxin response factor (ARF) transcription factors and their interacting auxin/indole-3-acetic acid (Aux/IAA) transcriptional inhibitors. Auxin promotes the degradation of Aux/IAA proteins through the auxin receptor and hence releases the inhibition of ARF transcription factors.

Green beginnings - pattern formation in the early plant embryo.

Embryogenesis in plants transforms the zygote into a relatively simple structure, the seedling, which contains all tissues and organs that later form the mature plant body. Despite a profound diversity in cell division patterns among plant species, embryogenesis yields remarkably homologous seedling architectures. In this review, we describe the formative events during plant embryogenesis and discuss the molecular mechanisms that regulate these processes, focusing on Arabidopsis.

MONOPTEROS controls embryonic root initiation by regulating a mobile transcription factor.

Acquisition of cell identity in plants relies strongly on positional information, hence cell-cell communication and inductive signalling are instrumental for developmental patterning. During Arabidopsis embryogenesis, an extra-embryonic cell is specified to become the founder cell of the primary root meristem, hypophysis, in response to signals from adjacent embryonic cells. The auxin-dependent transcription factor MONOPTEROS (MP) drives hypophysis specification by promoting transport of the hormone auxin from the embryo to the hypophysis precursor.

Bimodular auxin response controls organogenesis in Arabidopsis.

Like animals, the mature plant body develops via successive sets of instructions that determine cell fate, patterning, and organogenesis. In the coordination of various developmental programs, several plant hormones play decisive roles, among which auxin is the best-documented hormonal signal. Despite the broad range of processes influenced by auxin, how such a single signaling molecule can be translated into a multitude of distinct responses remains unclear.