Molecular Landscape of Helopeltis theivora Induced Transcriptome and Defense Gene Expression in Tea

Abstract

Tea is the second most consumed beverage worldwide whose cultivation is greatly challenged by a large variety of biotic and abiotic stresses. Among the biotic factors, the hemipteran pest Helopeltis theivora Waterhouse is particularly devastating in Asia and Africa, rendering the crop unsuitable for any downstream processing. The present study, for the first time, endeavors to dissect the molecular events associated with such infestations and identify potential molecular protagonists influencing Helopeltis tolerance in Assam tea. We analyzed the transcriptome of infested tea plants having contrasting responses to pest feeding by suppression subtractive hybridization and quantified the relative abundances of defense-associated transcripts. We analyzed 445 unigenes derived from 1558 expressed sequence tags (ESTs) from three different infestation conditions. Our study indicate that defense responses to the pest greatly vary in temporal and cultivar-specific manner characterized by an exclusive upregulation of specific defense-associated genes in the tolerant cultivar. Moreover, it was observed that transcripts related to flavonoid biosynthesis, purine metabolism, formate metabolism, jasmonic acid biosynthesis and signaling, and cell wall metabolism are uniquely enriched in the same. Interestingly, those involved in caffeine biosynthesis remain comparatively low and unaltered. We report higher trichome densities on the abaxial surface of the leaf in tolerant cultivar while puncture causes their tender reorientation. SEM of the insect mouthparts reveal higher concentrations of sensilla-like structures near the distal end and tip of the proboscis which are known to act as chemoreceptors in other hemipterans. Our investigation provides the first ever glimpse of Helopeltis-induced defense gene network and provides the much needed platform for improvement of the crop for better Helopeltis tolerance through breeding and transgenic approaches. On a wider perspective, the study will augment our understanding of molecular responses to phloem herbivory in plants.