Silencing of the Ornithine Decarboxylase Gene of Fusarium oxysporum f. sp. lycopersici by Host-Induced RNAi Confers Resistance to Fusarium Wilt in Tomato

Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici, a hemibiotrophic filamentous fungal pathogen is one of the important diseases of tomato. Recently, RNA interference (RNAi) has emerged as a novel alternative strategy for the control of plant diseases caused by fungal pathogens. Therefore, we tested the potential of RNAi for the control of Fusarium wilt in tomato by targeting a key polyamine (PA) biosynthesis gene, ornithine decarboxylase (ODC) of the pathogen as PAs (putrescine, spermidine, and spermine) are absolutely essential for normal growth and development. The target fungal ODC gene fragment was cloned in a hairpin RNA construct, which was used to develop several transgenic tomato plants. These RNAi transgenic lines expressed the intended small interfering RNAs (siRNAs) and exhibited moderate to high resistance when challenged with the spores of F. oxysporum. Interestingly, the silencing effect was confined only to the fungal pathogen and had no influence on the plant ODC gene expression, polyamine levels, and morphology. These results confirm that the ODC gene is vital for fungal growth and is a suitable target for disease control through host-induced gene silencing (HIGS) and also implicates the transfer of dsRNA/siRNAs from host plant cells to the fungal cells. To further validate the uptake of plant-derived siRNAs by fungal cells in a visual manner, silencing of the GFP transgene was observed in F. oxysporum GFP transformants upon infecting the dsGFP-expressing transgenic tomato plants. These experiments demonstrate the applicability of RNAi-based approach for crop protection from the filamentous fungal pathogens.