Investigation of two homologues of Auxin Binding Protein 1 (ABP1) in the moss Physcomitrella patens

Abstract

Auxin Binding Protein 1 (ABP1) is present in all plants, from some algae and bryophytes to angiosperms. It is central to the plants responsiveness to auxin. The bryophytes are a polyphyletic group, evolutionarily basal to the seed plants: the embryophytes, and Physcomitrella patens is their best known member. Studies have shown that ABP1 in Physcomitrella is unusual in that the genome contains two copies of the gene, each slightly different from the other, and that it lacks a KDEL motif that is present on the ABP1s from the higher plants. The KDEL motif in the higher plants serves to localise the ABP1 to the endoplasmic reticulum, so there is a mystery as to where it is localised in Physcomitrella. In this study I established that both of the two copies of the ABP1 gene are expressed during moss development. To assess the function of ABP1 both copies of ABP1 were separately knocked out and investigated to determine what effect that had on both the physical phenotype and on the molecular responses to exogenous auxin. Furthermore, the localisation of the ABP1s was probed by means of ABP1 fusion with Yellow Fluorescent Protein (YFP). Confocal laser scanning fluorescence microscopy was to be used to show where within the Physcomitrella cells the ABP1/YFP accumulated. Knowledge of how auxin is sensed by ABP1 in Physcomitrella illuminates how it is similarly sensed in the more economically important higher plants.