Plants are able to orient their growth according to gravity, which ultimately controls both shoot and root architecture.¹ Gravitropism is a dynamic process whereby gravistimulation induces the asymmetric distribution of the plant hormone auxin, leading to asymmetric growth, organ bending, and subsequent reset of auxin distribution back to the original pre-gravistimulation situation.1, 2, 3 Differential auxin accumulation during the gravitropic response depends on the activity of polarly localized PIN-FORMED (PIN) auxin-efflux carriers.1, 2, 3, 4 In particular, the timing of this dynamic response is regulated by PIN2,^5,6 but the underlying molecular mechanisms are poorly understood. Here, we show that MEMBRANE ASSOCIATED KINASE REGULATOR2 (MAKR2) controls the pace of the root gravitropic response. We found that MAKR2 is required for the PIN2 asymmetry during gravitropism by acting as a negative regulator of the cell-surface signaling mediated by the receptor-like kinase TRANSMEMBRANE KINASE1 (TMK1).^2,7, 8, 9, 10 Furthermore, we show that the MAKR2 inhibitory effect on TMK1 signaling is antagonized by auxin itself, which triggers rapid MAKR2 membrane dissociation in a TMK1-dependent manner. Our findings suggest that the timing of the root gravitropic response is orchestrated by the reversible inhibition of the TMK1 signaling pathway at the cell surface.

植物能够根据重力定向生长，最终控制地上部和根系结构。¹向地性是一个动态过程，重力刺激诱导植物激素生长素的不对称分布，导致生长不对称、器官弯曲，随后生长素分布重新回到重力刺激前的原始状态。 1, 2, 3 不同的生长素积累过程向重力响应取决于极性定位的 PIN-FORMED (PIN) 生长素外排载体的活性。 1, 2, 3, 4 特别是，这种动态响应的时间由 PIN2, ^{5 , 6}调节但其潜在的分子机制知之甚少。在这里，我们展示了膜相关激酶调节剂 2 (MAKR2) 控制根向重力响应的速度。我们发现 MAKR2 在向重性过程中是 PIN2 不对称所必需的，它是受体样激酶 TRANSMEMBRANE KINASE1 (TMK1) 介导的细胞表面信号传导的负调节因子。^{2 ,} 7, 8, 9, 10 此外，我们表明 MAKR2 对 TMK1 信号传导的抑制作用被生长素本身拮抗，这会以 TMK1 依赖性方式触发 MAKR2 膜的快速解离。我们的研究结果表明，根向重反应的时间是由细胞表面 TMK1 信号通路的可逆抑制所协调的。