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. 2017 Sep 29;9(10):280. doi: 10.3390/v9100280

Figure 2.

Figure 2

A working model for the role of Cotton leaf curl Multan betasatellite (CLCuMuB) βC1 protein in disease progression and suppression of host defense. Black arrows indicate un-interrupted virus infection cycle, blue arrows represent host defense mechanisms, green arrows represent βC1 interaction with host proteins, orange arrows represent the repression of leaf curl disease symptoms and red arrows represent the counter-defense mechanisms triggered by CLCuMuB βC1. Begomoviruses associated with cotton leaf curl disease (CLCuVs), along with CLCuMuB, produce transcripts of virus genes and βC1, respectively. In an un-interrupted disease infection cycle, these transcripts are translated in respective proteins, that in-turn interact with several cellular proteins that induces typical leaf curl disease symptoms. But usually the viral transcripts are targeted by the host’s RNA interference (RNAi) machinery that subsequently degrades the viral gene transcripts in a process called post-transcriptional gene silencing (PTGS) and interferes with disease progression and symptom development. CLCuMuB βC1 has been reported to interact with host protein AGO1 and acts as a strong suppressor of PTGS; this assisting the helper virus in normal disease progression and symptom development. CLCuMuB βC1 can also suppress systemic gene silencing, resulting in reduced levels of viral siRNAs. Viral proteins and βC1 are also targeted by cellular autophagy machinery that degrades these proteins through a cellular mechanism called ubiquitination. Host protein ATG8 has been reported to interact with CLCuMuB βC1 in an attempt to induce autophagy. CLCuMuB βC1 has also been reported to interact with a cellular protein UBC, and this interaction interferes with the ubiquitination, leading the infected cells towards disease progression and symptom development. It must be noted that only the functional roles of CLCuMuB βC1, and among those only the ones that are experimentally confirmed, have been shown here; the functions and βC1-host protein interaction may vary for different species of betasatellites.