Genomic Analysis of Cotton Pests

Upland cotton (Gossypium hirsutum) is an important crop in Mississippi. Economic losses are incurred every year due to the feeding and treatment of crop pests and plant pathogens. Because it is often unclear what differentiates a pest from a pathogen, I will use the umbrella term “biotic stressor” or BST when referring to a plant pest or pathogen. BSTs employ a special set of proteins known as ‘effectors’ that function at the site of BST physical attack. Effectors dictate how the host-BST relationship will unfold. Effectors include the proteins produced by the BST that are recognized by the plant and invoke the subsequent plant immune responses to the BST. Moreover, some effectors are responsible for the successful modification of the host tissues for the survival of the pest. In this study I utilized Illumina sequencing and computational biology approaches to identify effectors within three evolutionarily diverse cotton BSTs; specifically, Lygus lineolaris (tarnished plant bug), Xanthomonas citri pv. malvacearum (Xcm) (bacterial cotton blight), and Rotylenchulus reniformis (reniform nematode). Transcripts from the Lygus lineolaris salivary gland were found to encode putative degradative proteins used for the extra-oral digestion of host tissues by the insect. Production, assembly, and comparison of a whole genome assembly of the first Xcm genome obtained from a strain isolated in the cotton producing region of the United States revealed that the cotton Xcm is similar to other reported Xcm assemblies and contains most of the proteins found in these other strains. Genome and life-stage specific transcriptome sequencing of the nematode Rotylenchulus reniformis resulted in the identification of 41,570 transcripts of which 3,033 were up-regulated in the parasitic sedentary female life-stage. These studies collectively provide insight into the mechanisms by which key cotton BSTs invade and damage cotton. Further study of the BST effectors and the plant biomolecules with which they interact should facilitate development of highly targeted mechanisms of minimizing/eliminating BST damage. Such customized BST management will increase profits for farmers and maximize resource utilization in an environmentally responsible manner