The auxin and ethylene pathways cooperatively regulate a variety of developmental processes in plants. Growth responses to ethylene are largely dependent on auxin, the key regulator of plant morphogenesis. Auxin, in turn, is capable of inducing ethylene biosynthesis and signaling, making the interaction of these hormones reciprocal. Recent studies discovered a number of molecular events underlying auxin-ethylene crosstalk. In this review, we summarize the results of fine-scale and large-scale experiments on the interactions between the auxin and ethylene pathways in Arabidopsis. We integrate knowledge on molecular crosstalk events, their tissue specificity, and associated phenotypic responses to decipher the crosstalk mechanisms at a systems level. We also discuss the prospects of applying systems biology approaches to study the mechanisms of crosstalk between plant hormones.

Expansins facilitate cell expansion via mediating pH-dependent cell wall (CW) loosening. However, the role of expansins in the control of biomechanical CW properties in the tissue and organ context remains elusive. We determined hormonal responsiveness and specificity of expression and localization of expansins predicted to be direct targets of cytokinin signalling. We found EXPA1 homogenously distributed throughout the CW of columella/ lateral root cap, while EXPA10 and EXPA14 localized predominantly at the three-cell boundaries of epidermis/cortex in various root zones. Cell type-specific localization of EXPA15 overlaps with higher CW stiffness measured via Brillouin light scattering microscopy. As indicated by both Brillouin frequency shift and AFM-measured Young’s modulus, EXPA1 overexpression upregulated CW stiffness, associated with shortening of the root apical meristem and root growth arrest. We propose that root growth in Arabidopsis requires delicate orchestration of biomechanical CW properties via tight regulation of various expansins’ localization to specific cell types and extracellular domains.

Auxin and ethylene pathways cooperatively regulate a variety of developmental processes in plants. Growth responses to ethylene are largely dependent on auxin, the key regulator of plant morphogenesis. Auxin, in turn, is capable of inducing ethylene biosynthesis and signaling making the interaction of these hormones reciprocal. Recent studies discovered a bunch of molecular events underlying auxin-ethylene crosstalk. In this review, we summarize the results of fine-scale and large-scale experiments on interaction of auxin and ethylene pathways in Arabidopsis. We integrate the knowledge on the molecular crosstalk events, their tissue specificity and associated phenotypic responses to decipher the crosstalk mechanisms at a systems level. We also discuss the prospects of applying systems biology approaches to study the mechanisms of crosstalk between plant hormones.