Auxin efflux by PIN-FORMED proteins is activated by two different protein kinases, D6 PROTEIN KINASE and PINOID.

The development and morphology of vascular plants is critically determined by synthesis and proper distribution of the phytohormone auxin. The directed cell-to-cell distribution of auxin is achieved through a system of auxin influx and efflux transporters. PIN-FORMED (PIN) proteins are proposed auxin efflux transporters, and auxin fluxes can seemingly be predicted based on the--in many cells--asymmetric plasma membrane distribution of PINs. Here, we show in a heterologous Xenopus oocyte system as well as in Arabidopsis thaliana inflorescence stems that PIN-mediated auxin transport is directly activated by D6 PROTEIN KINASE (D6PK) and PINOID (PID)/WAG kinases of the Arabidopsis AGCVIII kinase family. At the same time, we reveal that D6PKs and PID have differential phosphosite preferences. Our study suggests that PIN activation by protein kinases is a crucial component of auxin transport control that must be taken into account to understand auxin distribution within the plant.

A large number of tetraploid Arabidopsis thaliana lines, generated by a rapid strategy, reveal high stability of neo-tetraploids during consecutive generations.

Arabidopsis thaliana has, in conjunction with A. arenosa, developed into a system for the molecular analysis of alloplolyploidy. However, there are very few Arabidopsis lines available to study autopolyploidy. In order to investigate polyploidy on a reliable basis, we have optimised conventional methodologies and developed a novel strategy for the rapid generation and identification of polyploids based on trichome branching patterns. The analysis of more than two dozen independently induced Arabidopsis lines has led to interesting observations concerning the relationship between cell size and ploidy levels and on the relative stability of tetraploidy in Arabidopsis over at least three consecutive generations. The most important finding of this work is that neo-tetraploid lines exhibit considerable stability through all the generations tested. The systematic generation of tetraploid collections through this strategy as well as the lines generated in this work will help to unravel the consequences of polyploidy, particularly tetraploidy, on the genome, on gene expression and on natural diversity in Arabidopsis.