PTGS depends upon {TAIL ~ transcription} of {HEAD ~ the initiating transgene} to function and so if this gets reduced the PTGS will begin to fail 
PTGS depends upon { TAIL ~ transcription } of { HEAD ~ the initiating transgene } to function and so if this gets reduced the PTGS will begin to fail
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH