摘要The phragmoplast,a structure crucial for the completion of cytokinesis in plant cells,is com-posed of antiparallel microtubules(MTs)and actin filaments(AFs).However,how the parallel structure of phragmoplast MTs and AFs is maintained,es-pecially during centrifugal phragmoplast ex-pansion,remains elusive.Here,we analyzed a new Arabidopsis thaliana MT and AF crosslinking pro-tein(AtMAC).When AtMAC was deleted,the phragmoplast showed disintegrity during cen-trifugal expansion,and the resulting phragmoplast fragmentation led to incomplete cell plates.Over-expression of AtMAC increased the resistance of phragmoplasts to depolymerization and caused the formation of additional phragmoplasts during cytokinesis.Biochemical experiments showed that AtMAC crosslinked MTs and AFs in vitro,and the truncated AtMAC protein,N-CC1,was the key do-main controlling the ability of AtMAC.Further analysis showed that N-CC1(51-154)is the key domain for binding MTs,and N-CC1(51-125)for binding AFs.In conclusion,AtMAC is the novel MT and AF crosslinking protein found to be involved in regulation of phragmoplast organization during centrifugal phragmoplast expansion,which is required for complete cytokinesis.