Abstract

Plants rely on local accumulation of the phytohormone auxin for a wide range of processes crucial for functional development. In the plant shoot, local auxin maxima specify initiation sites for new organs, such as flowers. Active transport of auxin by PIN proteins, which polarise on cell membranes, is a primary driver for the formation of auxin maxima, but the intricacies of PIN -mediated auxin transport is not fully understood. To this end, we have combined computational and experimental approaches to quantitatively assess the cellular abundance and polarity patterning of the auxin efflux carrier PIN1 , as well as the resulting auxin pattern following comprehensive simulations of auxin transport as mediated by active and passive transport mechanisms. We find that our PIN1 has strong abundance and polarity patterning correlating strongly with the developmental stage of establishing primordia, both in the epidermis and provasculature. Further, our model suggests that resulting local PIN1 and auxin maxima have shifted profiles relative to the developmental stage of the corresponding primordium, implicating a time-scale for PIN1 -auxin feedback coupling. In addition, we analyse the patterning of auxin in meristems with computationally modified patterning of auxin transport proteins, and provide patterning-based explanatory mechanisms for experimentally observed phenotypes. Lastly, we correlate the geometric properties of cells with the output of our analysis and model, linking the timing of local maxima in the shoot to the development of morphologically relevant cellular features.