The transition to terrestrial plants was accompanied by a progressive loss of microtubule minus end-directed dynein motors. Instead, the minus-end directed class-XIV kinesins expanded considerably, probably related to novel functions. One of these motors, OsDLK (Dual Localisation Kinesin from rice) decorates cortical microtubules but moves into the nucleus in response to cold stress. This analysis of loss-of-function mutants in rice indicates that OsDLK participates in cell elongation during development. Since OsDLK harbours both, a nuclear localisation signal, and a putative leucin zipper, we asked, whether the cold-induced import of OsDLK into the nucleus might correlate with a specific DNA binding. Conducting a DPI-ELISA screen with recombinant OsDLKT (lacking the motor domain), we identified the Opaque2 motif as most promising candidate. This motif is present in the promoter of NtAvr9/Cf9, the tobacco homologue of Cold Box Factor 4, a transcription factor involved in cold adaptation. A comparative study revealed that the cold-induced accumulation of NtAvr9/Cfp9 was specifically quelled in transgenic BY-2 cells overexpressing OsDLK-GFP. These findings are discussed as a working model, where, in response to cold stress, OsDLK partitions from cortical microtubules at the plasma membrane into the nucleus and specifically modulates the expression of genes involved in cold adaptation.

A grapevine cell line, where actin filaments are labelled by GFP, was used to show that aluminium causes actin remodeling through activation of a NADPH oxidase in the plasma membrane, followed by activation of phytoalexin synthesis genes. Elimination of actin filaments by Latrunculin B disrupts the gene activation, inhibition of MAPK signalling by the inhibitor PD98059 as well. Interestingly, aluminum also induces transcripts for ISOCHORISMATE SYNTHASE, as well as of PR1, which are known to be responsive to salicylic acid. However, aluminium-triggered defence is not as SA responses accompanied by cell death. Also in grapevine leaf discs from two genotypes contrasting in stilbene inducibility, aluminum can induce accumulation of a central grapevine phytoalexins, the stilbene aglycone trans-resveratrol, preceded by a rapid induction of transcripts for RESVERATROL SYNTHASE and the regulating transcription factor MYB14. The amplitude of this induction reflects the general stilbene inducibility of these genotypes, indicating that the aluminum effect is not caused by unspecific toxicity, but by activation of specific signalling. The findings show that, actin filaments activate a specific branch of defence signalling acting in concert with calcium-dependent PAMP triggered immunity. This pathway links apoplastic oxidative burst through MAPK signalling with the activation of defence-related transcripts.