Identification of Effector Candidates in Fall Armyworm ( Spodoptera frugiperda ) via Secretome Prediction and Infestation Assay

ABSTRACT Effector proteins, one of the major components of insect salivary glands, function to alter host defence mechanisms and facilitate pests for successful infestation. The fall armyworm, Spodoptera frugiperda , is a polyphagous lepidopteran insect that infests a wide range of agricultural crops. Despite being one of the world's most devastating pests, not much is known about the effector proteins of S. frugiperda . In this study, we conducted an in silico analysis of interproscan‐annotated protein sequences derived from the S. frugiperda transcriptome using established secretome prediction pipelines. Out of 21,779 protein sequences of S. frugiperda , 821 proteins were predicted to be secretory in nature, resulting in the generation of an in silico secretome database for S. frugiperda . The proteins in the S. frugiperda secretome were categorised into different functional groups based on their annotated functions. From these data, genes corresponding to 20 protein candidates were selected on the basis of their functions and previous literature available, and a comparative analysis of their transcript levels in the salivary glands of S. frugiperda larvae fed on artificial diet versus tomato plants was performed. Three genes—a serine protease , a BCL co‐repressor and a REPAT family gene—were found to be significantly upregulated in the salivary glands of S. frugiperda larvae fed on tomato plants. This highlights their secretory potential and possible involvement in host infestation. These findings signify that the predicted secretome, the first ever for S. frugiperda , can serve as a valuable resource for the identification of secreted proteins. This will pave the way for discovering potential effector proteins in S. frugiperda that play crucial roles in suppressing plant immune responses.