Arabidopsis KASH domains are differentially required for distinct LINC complex roles in stomata, roots and pollen.

Nuclear movement and positioning can be mediated by linker of nucleoskeleton and cytoskeleton (LINC) complexes, which consist of Sad1-UNC-84 (SUN) proteins and Klarsicht-ANC-1-Syne homology (KASH) proteins. KASH proteins bind SUN proteins via a short KASH domain. Unlike animal KASH domains, plant KASH domains are shorter, lack ability to form disulfide bonds and have a different C-terminal sequence motif. Here, we examined the specificity of KASH domains using two Arabidopsis KASH proteins, WIP1 and SINE1. We show experimentally that the SINE1 KASH domain is required for SINE1 function in stomata and the WIP1 KASH domain for WIP1 function in root hairs, but that the SINE1 and WIP1 KASH domains are interchangeable for the WIP1 role in nuclear movement in pollen tubes. Through molecular modeling, we found that SINE1 has two distinct binding modes that are dependent on its interaction partner (SUN1 or SUN2), whereas WIP1 binds very similarly to both SUN1 and SUN2. We propose that this requirement for specific KASH domains reflects differences between the SUN1-SINE1 and SUN1-WIP1 interaction models and might indicate a different tolerance of the interactions to force.