Paxillin protein PaxB and actinin-like protein AcnA are required for cytokinesis via regulating actin ring assembly in Aspergillus nidulans

Cytokinesis, as the final step of cell division, plays an important role in fungal growth and proliferation. In filamentous fungus Aspergillus nidulans, abnormal multinuclear or non–nucleated cells induced by defected cytokinesis will cause defected hyphal growth and sporulation. Previous studies have demonstrated that proper cytokinesis is accompanied with actin ring formation and contraction, which are regulated by (SIN) septation–initiation network that is consist of several conserved components. In our previous study, we found that actinin-like protein AcnA is essential for cytokinesis but underlined relationship between AcnA and SIN or between AcnA and actin cytoskeleton are not known yet.

In the present study, we have identified a cytoskeletal protein paxillin PaxB has a similar phenotype to that of AcnA, suggesting it is also essential for cytokinesis. In the absence of AcnA or PaxB, a key component of SIN pathway -MobA, was unable to contract at the predict septation site. Comparably, loss of function of SIN pathway could affect localization of AcnA and PaxB at the septation site. These results suggest that two cytoskeletal proteins AcnA and PaxB and the SIN pathway are reciprocal required to drive the proper cytokinesis. Moreover, deletion of acnA or paxB caused actin rings disappeared，which implies that AcnA and PaxB are crucial for actin ring formation. In addition, deletion of acnA leads to undetectable PaxB at the septation site, in comparison, deletion of paxB did not affect the location of AcnA but block its contraction during cytokinesis, which demonstrate that AcnA and PaxB are required for the function of each other. In paxB deletion mutant strains, septation and sporulation defects can be rescued by overexpressed acnA. These data suggest that AcnA and PaxB probably have an overlapping function for the proper function of SIN pathway and the formation of actin ring in A. nidulans.