Many biological processes require the co-operative involvement of both microtubules and microfilaments; however, only a few proteins mediating the interaction between microtubules and microfilaments have been identified from plants. In the present study, a cotton kinesin GhKCH2, which contains a CH (calponin homology) domain at the N-terminus, was analysed in vitro and in vivo in order to understand its interaction with the two cytoskeletal elements. A specific antibody against GhKCH2 was prepared and used for immunolabelling experiments. Some GhKCH2 spots appeared along a few microtubules and microfilaments in developing cotton fibres. The His-tagged N-terminus of GhKCH2 (termed GhKCH2-N) could co-precipitate with microfilaments and strongly bind to actin filaments at a ratio of monomeric actin/GhKCH2-N of 1:0.6. The full-length GhKCH2 recombinant protein was shown to bind to and cross-link microtubules and microfilaments in vitro. A GFP-fusion protein GFP–GhKCH2 transiently overexpressed in Arabidopsis protoplasts decorated both microtubules and microfilaments, confirming the binding ability and specificities of GhKCH2 on microtubules and microfilaments in living plant cells. The results of the present study demonstrate that GhKCH2, a plant-specific microtubule-dependent motor protein, not only interacts with microtubules, but also strongly binds to microfilaments. The cytoskeletal dual-binding and cross-linking ability of GhKCH2 may be involved in the interaction between microtubules and microfilaments and the biological processes they co-ordinate together in cotton cells.

MPK3/6 is responsible for phosphorylation of SPOROCYTELESS/NOZZLE protein, which is required for its function in Arabidopsis anther development.

Ethylene response factor (ERF) Group VII members generally function in regulating plant growth and development, abiotic stress responses, and plant immunity in Arabidopsis; however, the details of the regulatory mechanism by which Group VII ERFs mediate plant immune responses remain elusive. Here, we characterized one such member, ERF72, as a positive regulator that mediates resistance to the necrotrophic pathogen Botrytis cinerea. Compared with the wild-type (WT), the erf72 mutant showed lower camalexin concentration and was more susceptible to B. cinerea, while complementation of ERF72 in erf72 rescued the susceptibility phenotype. Moreover, overexpression of ERF72 in the WT promoted camalexin biosynthesis and increased resistance to B. cinerea. We identified the camalexin-biosynthesis genes PAD3 and CYP71A13 and the transcription factor WRKY33 as target genes of ERF72. We also determined that MPK3 and MPK6 phosphorylated ERF72 at Ser151 and improved its transactivation activity, resulting in increased camalexin concentration and increased resistance to B. cinerea. Thus, ERF72 acts in plant immunity to coordinate camalexin biosynthesis both directly by regulating the expression of biosynthetic genes and indirectly by targeting WRKK33.

Mitogen-activated protein kinases (MAPKs) are involved in the regulation of plant growth, development and responses to a wide variety of stimuli. In a conditional gain-of-function transgenic system, the activation of AtMEK5, a MAPK kinase, can in turn activate endogenous AtMAPK3 and AtMAPK6, and can lead to a striking increase in ethylene production and induce hypersensitive response (HR)-like cell death in Arabidopsis. However, the role of the increased ethylene production in regulating this HR-like cell death remains unknown. Using Arabidopsis transgenic plants that express AtMEK5^DD, an active mutant of AtMEK5 that is under the control of a steroid-inducible promoter, we tested the contribution of ethylene to cell death. We found that ethylene biosynthesis occurs before cell death. Cell death was delayed by inhibiting AtMEK5-induced ethylene production using inhibitors of ACC-synthases, ACC-oxidases or ethylene receptors. In the mutants AtMEK5^DD/etr1-1 and AtMEK5^DD/ein2-1, both of which showed insensitivity to ethylene, the expression of AtMEK5^DD protein, activity of AtMAPK3 and AtMAPK6, and ethylene production were the same as those seen in AtMEK5^DD transgenic plants, but cell death was also delayed. These data suggest that ethylene signaling perception is required to accelerate cell death that is induced by AtMEK5 activation.