Cytokinin response factors regulate PIN-FORMED auxin transporters.

Auxin and cytokinin are key endogenous regulators of plant development. Although cytokinin-mediated modulation of auxin distribution is a developmentally crucial hormonal interaction, its molecular basis is largely unknown. Here we show a direct regulatory link between cytokinin signalling and the auxin transport machinery uncovering a mechanistic framework for cytokinin-auxin cross-talk.

Polarized cell growth in Arabidopsis requires endosomal recycling mediated by GBF1-related ARF exchange factors.

Polarized tip growth is a fundamental cellular process in many eukaryotic organisms, mediating growth of neuronal axons and dendrites or fungal hyphae. In plants, pollen and root hairs are cellular model systems for analysing tip growth. Cell growth depends on membrane traffic.

Molecular and cellular aspects of auxin-transport-mediated development.

The plant hormone auxin is frequently observed to be asymmetrically distributed across adjacent cells during crucial stages of growth and development. These auxin gradients depend on polar transport and regulate a wide variety of processes, including embryogenesis, organogenesis, vascular tissue differentiation, root meristem maintenance and tropic growth. Auxin can mediate such a perplexing array of developmental processes by acting as a general trigger for the change in developmental program in cells where it accumulates and by providing vectorial information to the tissues by its polar intercellular flow.

Functional redundancy of PIN proteins is accompanied by auxin-dependent cross-regulation of PIN expression.

Plant development displays an exceptional plasticity and adaptability that involves the dynamic, asymmetric distribution of the phytohormone auxin. Polar auxin flow, which requires polarly localized transport facilitators of the PIN family, largely contributes to the establishment and maintenance of the auxin gradients. Functionally overlapping action of PIN proteins mediates multiple developmental processes, including embryo formation, organ development and tropisms.

Partial loss-of-function alleles reveal a role for GNOM in auxin transport-related, post-embryonic development of Arabidopsis.

The Arabidopsis GNOM gene encodes an ARF GDP/GTP exchange factor involved in embryonic axis formation and polar localisation of the auxin efflux regulator PIN1. To examine whether GNOM also plays a role in post-embryonic development and to clarify its involvement in auxin transport, we have characterised newly isolated weak gnom alleles as well as trans-heterozygotes of complementing strong alleles. These genotypes form a phenotypic series of GNOM activity in post-embryonic development, with auxin-related defects, especially in the maintenance of primary root meristem activity and in the initiation and organisation of lateral root primordia.

Efflux-dependent auxin gradients establish the apical-basal axis of Arabidopsis.

Axis formation occurs in plants, as in animals, during early embryogenesis. However, the underlying mechanism is not known. Here we show that the first manifestation of the apical-basal axis in plants, the asymmetric division of the zygote, produces a basal cell that transports and an apical cell that responds to the signalling molecule auxin.