Zhou et al. reveal that plants express diverse KASH-like proteins that perform discrete functions at the outer nuclear membrane.
In animals and fungi, LINC complexes—composed of inner nuclear membrane SUN proteins and outer nuclear membrane KASH proteins—connect the nucleus to the cytoskeleton to control a variety of processes including nuclear positioning and chromatin organization. Plants express SUN proteins, but their genomes lack KASH homologues. They do, however, encode at least one family of proteins that, like animal and fungal KASH proteins, bind to SUN family members and localize to the outer nuclear membrane.
Zhou et al. devised a bioinformatic approach to identify additional SUN-binding proteins in Arabidopsis and other plant species, uncovering ten new families of potential KASH-like plant proteins. The researchers tested several of these new proteins and confirmed that they localize to the nuclear envelope by binding to members of the SUN family.
One new Arabidopsis KASH protein, which the researchers named SINE1, was strongly expressed in leaf guard cells, which control gas exchange by opening and closing stomata. SINE1 was required to anchor the nucleus in the center of each guard cell, probably by interacting with the actin cytoskeleton. Meanwhile, a paralogue of SINE1, SINE2, was expressed in the epidermal and mesophyll cells of Arabidopsis leaves and protected the plant from infection by an oomycete pathogen. Senior author Iris Meier now wants to investigate how SINE2 fights infection and to determine how defects in nuclear positioning affect the function of guard cells.
Text by Ben Short