The chaperonin CCT8 facilitates spread of tobamovirus infection.

The homeodomain transcription factor KNOTTED1 (KN1) functions in shoot meristem maintenance and is thought to move from cell to cell in a similar fashion as viral movement proteins. Both types of transported proteins bind to RNA, and associate with intercellular bridges formed by plasmodesmata. In a mutant screen for KN1 transport deficiency, a component of a type II chaperonin complex, CCT8, was identified, and found to interact with non-cell-autonomous proteins. The cct8 mutants are characterized by limited functionality of non-cell-autonomous proteins after their movement, and a phenotype resembling lack of homeodomain protein activity. Evidence suggests that CCT8 functions in post-translocational refolding of transported proteins. Here we show that spread of tobamovirus infection is reduced in a cct8 mutant. This suggests that similar to KN1, viral movement proteins are unfolded and refolded during transport to gain functionality in the receiving cells.