P1 protein of Cocksfoot mottle virus is indispensable for the systemic spread of the virusMeier, Merike; Paves, Heiti; Olspert, Allan; Tamm, Tiina; Truve, ErkkiVirus genes2006 / 3, p. 321-326 https://link.springer.com/article/10.1007/s11262-005-6917-x