Nuclear lamins are involved in multiple biological processes in metazoan cells. The proteins of the CROWDED NUCLEI (CRWN) family are considered lamin-like candidates in Arabidopsis, although the functions of these proteins are largely unknown. In this article we show that crwn1 crwn2 double mutant displays an enhanced resistance against virulent bacterial pathogens, and both virulent bacteria and salicylic acid (SA) induce transcription of CRWN1 gene as well as proteasome-mediated degradation of CRWN1 protein. We also show that CRWN1 interacts with NAC WITH TRANSMEMBRANE MOTIF1-LIKE9 (NTL9), a NAC transcription factor involved in plant immunity. The interaction between CRWN1 and NTL9 enhances the binding of NTL9 to the promoter of the PATHOGENESIS-RELATED1 (PR1) gene, and inhibits PR1 expression. Further genetic experiments indicated that the defense-related phenotypes of crwn1 crwn2 double mutant are dependent on NONEXPRESSOR OF PR GENES1 (NPR1), a transcriptional cofactor of PR1. These findings revealed a regulatory network composed of lamin-like protein CRWN1, NTL9, and NPR1 for the regulation of PR1 expression.

Plants cope with various recurring stress conditions that often induce DNA damage, ultimately affecting plant genome integrity, growth and productivity. The CROWDED NUCLEI (CRWN) family comprises lamin-like proteins with multiple functions, such as regulating gene expression, genome organization and DNA damage repair in Arabidopsis (Arabidopsis thaliana). However, the mechanisms and consequences of CRWNs in DNA damage repair are largely unknown. Here, we reveal that CRWNs maintain genome stability by forming repairing nuclear bodies at DNA double-strand breaks. We demonstrate that CRWN1 and CRWN2 physically associate with the DNA damage repair proteins RAD51D and SUPPRESSOR OF NPR1-1 Inducible 1 (SNI1) and act in the same genetic pathway to mediate this process. Moreover, CRWN1 and CRWN2 partially localize at γ-H2AX foci upon DNA damage. Notably, CRWN1 and CRWN2 undergo liquid-liquid phase separation to form highly dynamic droplet-like structures with RAD51D and SNI1 to promote the DNA damage response (DDR). Collectively, our data shed light on the function of plant lamin-like proteins in the DDR and maintenance of genome stability.