Editing eIF4E in the Watermelon Genome Using CRISPR/Cas9 Technology Confers Resistance to ZYMV

Watermelon is one of the most important cucurbit crops, but its production is seriously affected by viral infections. Although eIF4E proteins have emerged as the major mediators of the resistance to viral infections, the mechanism underlying the contributions of eIF4E to watermelon disease resistance remains unclear. In this study, three <i>CleIF4E</i> genes and one <i>CleIF(iso)4E</i> gene were identified in the watermelon genome. Among these genes, <i>CleIF4E1</i> was most similar to other known <i>eIF4E</i> genes. To investigate the role of <i>CleIF4E1</i>, CRISPR/Cas9 technology was used to knock out <i>CleIF4E1</i> in watermelon. One selected mutant line had an 86 bp deletion that resulted in a frame-shift and the expression of a truncated protein. The homozygous mutant exhibits developmental defects in plant growth, leaf morphology and reduced yield. Furthermore, the mutant was protected against the zucchini yellow mosaic virus, but not the cucumber green mottled mosaic virus. In summary, this study preliminarily clarified the functions of eIF4E proteins in watermelon. The generated data will be useful for elucidating eIF4E-related disease resistance mechanisms in watermelon. The tissue-specific editing of <i>CleIF4E1</i> in future studies may help to prevent adverse changes to watermelon fertility.