Dissection of the role and regulation of ABCB phosphorylation in root twisting and soil penetration

Immediately after germination, roots have to penetrate the soil in search of water and nutrients However, the soil often represents an unpenetrable barrier for roots Therefore, roots seek pores between clay particles and cracks in hard soil horizons through which they can pursue downward growth This exploratory growth encompasses a complex behaviour that involves waving and twisting However, the relative contributions of both processes to soil penetration have not yet been investigated systematically Here, we will focus on how root twisting is regulated and how this contributes to root growth in soil To achieve this, we will analyze the regulation of two ABCB-type transporters of the growth-regulating plant hormone auxin Defects in these transporters lead to excessive root twisting, suggesting that they are active components of the mechanisms that facilitate soil penetration We will adress the tissues in which these transporter should be active to suppress root twisting, analyse how they are regulated, and visualize the spatial and temporal dynamics of ABCB phosphorylation in a growing root Together, these findings will increase our understanding how roots grow and how root twisting contibutes to soil penetration