MxMPK6-2-bHLH104 interaction is involved in reactive oxygen species signaling in response to iron deficiency in apple rootstock

• Published in: Journal of experimental botany 2021-02, Vol.72 (5), p.1919-1932
• Main Authors: Li, Duyue, Sun, Qiran, Zhang, Guifen, Zhai, Longmei, Li, Keting, Feng, Yi, Wu, Ting, Zhang, Xinzhong, Xu, Xuefeng, Wang, Yi, Han, Zhenhai
• Format: Article
• Language: English
• Subjects: Anemia, Iron-Deficiency; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - metabolism; Gene Expression Regulation, Plant; Iron - metabolism; Malus - genetics; Malus - metabolism; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; Plant Proteins - genetics; Plant Proteins - metabolism; Reactive Oxygen Species - metabolism
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/eraa547

MxMPK6-2 is responsive to reactive oxygen species signaling, and phosphorylates a key positive regulator, MxbHLH104, as part of the Fe deficiency response in Malus xiaojinensis. Abstract Iron (Fe) is a trace element necessary for plant growth. Many land plants have evolved a set of mechanisms associated with the Fe absorption process to deal with the problem of insufficient Fe supply in the soil. During Fe absorption, reactive oxygen species (ROS) can be used as a signal to initiate a response to stress caused by Fe deficiency. However, the molecular mechanisms underlying the involvement of ROS in the Fe deficiency stress response remains unclear. In this study, we have identified a kinase, MxMPK6-2, from Malus xiaojinensis, an apple rootstock that is highly efficient at Fe absorption. MxMPK6-2 has been shown to be responsive to ROS signals during Fe deficiency, and MxMPK6-2 overexpression in apple calli enhanced its tolerance to Fe deficiency. We further screened for proteins in the Fe absorption pathway and identified MxbHLH104, a transcription factor which interacts with MxMPK6-2. MxbHLH104 can be phosphorylated by MxMPK6-2 in vivo, and we confirmed that its phosphorylation increased Fe absorption in apple calli under Fe deficiency, with the presence of ROS promoting this process. Overall, we have demonstrated that MxMPK6-2 is responsive to ROS signaling during Fe deficiency, and is able to control its response by regulating MxbHLH104.