植物免疫是植物响应病原体入侵产生的一系列反应的总和。病原菌侵染初期，病菌信号依赖细胞表面的模式识别受体（pattern recognition receptors，PRRs）进行识别，并通过其与相应共受体共同作用完成的受体样胞质激酶（receptor-like cytoplasmic kinases，RLCK）的磷酸化进行传递。RLCK-VII亚家族成员之一的BIK1，被发现是一种会聚的调节因子，不仅能够受多种免疫受体激活，还能够磷酸化修饰多种下游蛋白。由此，BIK1的调控机制成为植物免疫研究中的关键议题。早有研究提出BIK1在免疫激活时会从受体复合体中解离，另有研究提示配体诱导的内吞可能是介导BIK1解离的一种方式，但具体的机制尚不清晰。为了详细描述BIK1经历配体诱导的解离的机制，同时寻找BIK1动态调控的新组分，在已报道的BIK1互作质谱中，本研究选择了植物中能够介导内吞的蛋白DRP2B进行探究。
拟南芥DRP2B属于DRP-II亚家族，具有与动物中的发动蛋白dynamin相似的五个结构域，在生长发育和免疫中均有作用。前人的研究已经确认，DRP2B能够参与免疫受体FLS2的内吞从而调控植物免疫，但这一途径不足以解释drp2b突变体呈现出的分支的免疫表型，其调控植物免疫的机制尚需进一步解析。
为了探究BIK1与DRP2B之间可能存在的互作对彼此的意义，本研究首先通过生物化学实验和活体成像技术确认了两者在植物体外与体内的相互作用，基于BIK1具有的激酶活性，进一步通过体外生物化学实验检测到了BIK1对DRP2B的体外磷酸化，并查找到了7个关键的体外磷酸化位点。随后对这7个位点进行突变后转入drp2b背景的拟南芥株系进行免疫表型检测，发现这7个位点影响到DRP2B在植物免疫中的正向调控作用。本研究还通过细胞学手段对BIK1和DRP2B免疫激活时的膜上动态进行了描述，发现BIK1经历免疫激活时动态变快，且这种变化与其激酶活性紧密相关，同样地，DRP2B也经历免疫激活时动态变快的过程，该变化能够被上述7个体外磷酸化位点的突变破坏。
综上所述，本研究确认了BIK1与DRP2B间的相互作用，并初步探索到BIK1对DRP2B的磷酸化在植物免疫中的意义，不仅如此，本研究描述了BIK1经历免疫激活时的动态变化及一种可能的影响因素，为BIK1的动态调控补充了一种新的可能组分，也为DRP2B调控免疫的机制提供了一条新的路线。

Plant immunity system consists of a series of responses triggered by pathogens. In the early stage of pathogen infection, cell surface-localized pattern recognition receptors (PRRs) identify pathogen signals, form receptor complex with their co-factors and then activate receptor-like cytoplasmic kinases (RLCK) by phosphorylation. BIK1, a member of the RLCK-VII subfamily, has been found to be a convergent regulatory factor that can not only be activated by various immune receptor complexes, but also impact on various downstream components. Therefore, the regulation of BIK1 has become a key issue in related research. 
Previous studies have suggested that BIK1 dissociates from the receptor complex during immune activation, while another recent study suggests that ligand-induced endocytosis may be a way to mediate BIK1 dissociation, yet the details are not clear.
In order to explicate the mechanism underlying ligand-induced dissociation of BIK1 and to identify new components for dynamic regulation of BIK1, based on the reported mass spectrometry, we focus on DRP2B, an endocytic component, for exploration in this study.
Arabidopsis DRP2B belongs to the DRP-II subfamily and has five structural domains similar to the dynamin in animals, which plays a role in plant development and immunity. A previous study reported that DRP2B could participate in the endocytosis of FLS2, the receptor for bacterial flagellin, thereby regulating plant immunity. However, data from this study are not sufficient for explaining the branched immune phenotype of drp2b, and the precise function of DRP2B in regulating plant immunity requires further investigation.
In order to explore the potential interaction between BIK1 and DRP2B and the impact they have on each other, we first confirmed the interaction between these two proteins in vitro and in vivo via biochemical experiments and in vivo imaging technology. We also found that BIK1 can phosphorylate DRP2B in vitro, and seven key phosphorylation sites were identified. DRP2B mutant protein with these seven sites mutated to alanine failed to complement the disease phenotype of drp2b, suggesting that the phosphorylation of DRP2B by BIK1 is critical for plant immunity. 
Moreover, we also monitored the dynamics of BIK1 and DRP2B on the cell surface during immune activation by single-particle tracking. We observed that BIK1 spots dynamically appeared and disappeared from the plasma membrane. During immune activation, the rate of BIK1 turnover was significantly increased at the plasma membrane, and this requires its kinase activity. Similarly, DRP2B spots assembled and disassembled dynamically at the cell surface. The assembly/disassembly of DRP2B became much faster in cells with activated immune signaling than non-stimulated cells. The differences in the DRP2B dynamics upon immune activation is abrogated by the mutation of phosphorylation sites. Taken together, we confirmed the interaction between BIK1 and DRP2B. Moreover, we described the dynamic behaviors of BIK1 and DRP2B on plasma membrane during immune activation. The biological significance of BIK1 on DRP2B phosphorylation in plant immunity were also investigated in this work.