Functional conservation of EXA1 among diverse plant species for the infection by a family of plant viruses.

Since the propagation of plant viruses depends on various host susceptibility factors, deficiency in them can prevent viral infection in cultivated and model plants. Recently, we identified the susceptibility factor Essential for poteXvirus Accumulation 1 (EXA1) in Arabidopsis thaliana, and revealed that EXA1-mediated resistance was effective against three potexviruses. Although EXA1 homolog genes are found in tomato and rice, little is known about which viruses depend on EXA1 for their infection capability and whether the function of EXA1 homologs in viral infection is conserved across multiple plant species, including crops. To address these questions, we generated knockdown mutants using virus-induced gene silencing in two Solanaceae species, Nicotiana benthamiana and tomato. In N. benthamiana, silencing of an EXA1 homolog significantly compromised the accumulation of potexviruses and a lolavirus, a close relative of potexviruses, whereas transient expression of EXA1 homologs from tomato and rice complemented viral infection. EXA1 dependency for potexviral infection was also conserved in tomato. These results indicate that EXA1 is necessary for effective accumulation of potexviruses and a lolavirus, and that the function of EXA1 in viral infection is conserved among diverse plant species.