Similarly, the lack of three papain-like cysteine proteases most related to Rcr3pim in Arabidopsis mutants (i.e. pap1, pap4, and pap5) suppresses immunity to H. schachtii (Fig. 5B) Altogether, these findings position the inhibition of extracellular papain-like cysteine proteases by apoplastic effectors as an important regulatory process in plant innate immunity to cyst nematodes. Here, CTSB is linked to cyst.