Stomatal formation is regulated by multiple developmental and environmental signals, but how these signals are integrated to control this process is not fully understood. In Arabidopsis thaliana, the basic helix-loop-helix transcription factor SPEECHLESS (SPCH) regulates the entry, amplifying and spacing divisions that occur during stomatal lineage development. SPCH activity is negatively regulated by mitogen-activated protein kinase (MAPK)-mediated phosphorylation. Here, we show that in addition to MAPKs, SPCH activity is also modulated by brassinosteroid (BR) signalling. The GSK3/SHAGGY-like kinase BIN2 (BR INSENSITIVE2) phosphorylates residues overlapping those targeted by the MAPKs, as well as four residues in the amino-terminal region of the protein outside the MAPK target domain. These phosphorylation events antagonize SPCH activity and limit epidermal cell proliferation. Conversely, inhibition of BIN2 activity in vivo stabilizes SPCH and triggers excessive stomatal and non-stomatal cell formation. We demonstrate that through phosphorylation inputs from both MAPKs and BIN2, SPCH serves as an integration node for stomata and BR signalling pathways to control stomatal development in Arabidopsis.

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HighlightEthylene affects adventitious rooting by reducing indole-3-acetic acid (IAA) biosynthesis, but enhancing conversion into IAA of its precursor indole-3-butyric acid (IBA). This conversion, together with active IAA-cellular-influx, is essential for adventitious root formation.

Chronic idiopathic constipation, especially the slow transit type, is a troubling problem often afflicting young women. The pathophysiological basis for this entity is unknown, although a defective cholinergic innervation has been postulated. We tested the hypothesis that cholinergic colonic innervation is deranged in this condition by studying colonic motor activity after strong cholinergic stimulation with edrophonium chloride in 14 women complaining of slow transit constipation. Unlike healthy subjects, constipated patients showed minimal or no response to edrophonium injection. It is concluded that in slow transit constipation there is an important alteration of colonic cholinergic activity and that edrophonium chloride may represent a useful test drug for colonic pathophysiological investigations.