Proposed model of DCL involvement in PSTVd defense.

Abstract

<p>In WT, PSTVd is targeted by at least three DCL enzymes. It is not clear whether DCL1 also contributes to this targeting. 21 and 22nt vd-siRNAs are loaded into AGO1 and AGO2 whereas 24nt into AGO4 and AGO5. These vd-siRNAs are probably redirected to target the PSTVd genome. In DCL4i condition, DCL4 is strongly suppressed, thus PSTVd genome is processed preferentially by a combination of DCL2-DCL3. The contribution of DCL1 in this action remains open. The majority of vd-siRNA produced at this condition are of 22nt class followed by 24nt class. These are probably uptaken by AGO1, AGO2, AGO4 and AGO5 and are targeting the PSTVd genome in a highly efficiently manner, resulting in a strong reduction of PSTVd infectivity.</p