TWISTED DWARF1 regulates Arabidopsis stamen development by differential activation of ABCB-mediated auxin transport

Despite clear evidence that a local accumulation of auxin is likewise critical for male fertility, much less is known about the components that regulate auxin-controlled stamen development.In this study, we analyzed physiological and morphological parameters in mutants of key players of ABCB-mediated auxin transport and spatially and temporally dissected their expression on the protein level as well as auxin fluxes in the Arabidopsis stamens. Our analyses revealed that the FKBP42, TWISTED DWARF1 (TWD1), promotes stamen elongation and, to a lesser extent, anther dehiscence, as well as pollen maturation and thus is required for seed development. Most of the described developmental defects in twd1 are shared with the abcb1 abcb19 mutant, which can be attributed to the fact that TWD1 - as a described ABCB chaperon - is a positive regulator of ABCB1 and ABCB19-mediated auxin transport. However, reduced stamen number was dependent on TWD1 but not on investigated ABCBs, suggesting additional actors down-stream of TWD1. We predict an overall housekeeping function for ABCB1 during earlier stages, while ABCB19 seems to be responsible for the key event of rapid elongation at later stages of stamen development. Our data indicate that TWD1 controls stamen development by differential activation of ABCB-mediated auxin transport in the stamen.HighlightBy using a mix of phenotypical and imaging analyses, we here identify and functionally characterize a new master regulator of flower development.

Maturation of persistent and hyperpolarization-activated inward currents shapes the differential activation of motoneuron subtypes during postnatal development

The size principle underlies the orderly recruitment of motor units; however, motoneuron size is a poor predictor of recruitment amongst functionally defined motoneuron subtypes. Whilst intrinsic properties are key regulators of motoneuron recruitment, the underlying currents involved are not well defined. Whole-cell patch-clamp electrophysiology was deployed to study intrinsic properties, and the underlying currents, that contribute to the differential activation of delayed and immediate firing motoneuron subtypes. Motoneurons were studied during the first three postnatal weeks in mice to identify key properties that contribute to rheobase and may be important to establish orderly recruitment. We find that delayed and immediate firing motoneurons are functionally homogeneous during the first postnatal week and are activated based on size, irrespective of subtype. The rheobase of motoneuron subtypes become staggered during the second postnatal week, which coincides with the differential maturation of passive and active properties, particularly persistent inward currents. Rheobase of delayed firing motoneurons increases further in the third postnatal week due to the development of a prominent resting hyperpolarization-activated inward current. Our results suggest that motoneuron recruitment is multifactorial, with recruitment order established during postnatal development through the differential maturation of passive properties and sequential integration of persistent and hyperpolarization-activated inward currents.

TWISTED DWARF1 regulates Arabidopsis stamen development by differential activation of ABCB-mediated auxin transport

Despite clear evidence that a local accumulation of auxin is likewise critical for floral organ initiation than for vegetative tissues, much less is known about the molecular key players that regulate auxin-controlled flower development. Here, by an analysis of physiological and morphological parameters and by a spatial and temporal dissection of auxin fluxes and expression of key players of ABCB-mediated auxin transport in the Arabidopsis flower, we demonstrate a crucial role for the FKBP42, TWISTED DWARF1 (TWD1), in the regulation of flower development. Our analyses revealed that TWD1 promotes flower shape and number, stamen elongation, pollen maturation, nectary functionality and seed development. Most of the described developmental defects in twd1 are shared with the abcb1 abcb19 mutant, which can be attributed to the fact that TWD1 as a described ABCB chaperon is a positive regulator of ABCB1 and ABCB19-mediated auxin transport. We predict an overall housekeeping function for ABCB1 during earlier stages, while ABCB19 seems to be responsible for the key event of rapid elongation at later stages of stamen development. Our data indicate that TWD1 controls flower development by differential activation of ABCB-mediated auxin transport.