Secretory RING finger proteins function as effectors in a grapevine galling insect

Abstract

BackgroundAll eukaryotes share a conserved network of processes regulated by the proteasome and fundamental to growth, development, or perception of the environment, leading to complex but often predictable responses to stress. As a specialized component of the ubiquitin-proteasome system (UPS), the RING finger domain mediates protein-protein interactions and displays considerable versatility in regulating many physiological processes in plants. Many pathogenic organisms co-opt the UPS through RING-type E3 ligases, but little is known about how insects modify these integral networks to generate novel plant phenotypes.ResultsUsing a combination of transcriptome sequencing and genome annotation of a grapevine galling species, Daktulosphaira vitifoliae, we identified 138 putatively secretory protein RING-type (SPRINGs) E3 ligases that showed structure and evolutionary signatures of genes under rapid evolution. Moreover, the majority of the SPRINGs were more expressed in the feeding stage than the non-feeding egg stage, in contrast to the non-secretory RING genes. Phylogenetic analyses indicated that the SPRINGs formed clusters, likely resulting from species-specific gene duplication and conforming to features of arthropod host-manipulating (effector) genes. To test the hypothesis that these SPRINGs evolved to manipulate cellular processes within the plant host, we examined SPRING interactions with grapevine proteins using the yeast two-hybrid assay. An insect SPRING interacted with two plant proteins, a cellulose synthase, CSLD5, and a ribosomal protein, RPS4B suggesting secretion reprograms host immune signaling, cell division, and stress response in favor of the insect. Plant UPS gene expression during gall development linked numerous processes to novel organogenesis.ConclusionsTaken together, D. vitifoliae SPRINGs represent a novel gene expansion that evolved to interact with Vitis hosts. Thus, a pattern is emerging for gall forming insects to manipulate plant development through UPS targeting.

Cytokinins Are Abundant and Widespread among Insect Species

“…Furthermore, in the Hessian fly system, no covering gall is present, so whatever effectors may be found could only contribute to the generation of the nutritive layer. Nonetheless, it is possible that effector proteins [105], or other effectors in addition to phytohormones, contribute to gall induction. Further research will be necessary to either establish or rule out a contribution for proteinaceous or other non-protein effectors in gall induction.…”

Comparative Transcriptome Analysis of Two Root-Feeding Grape Phylloxera (D. vitifoliae) Lineages Feeding on a Rootstock and V. vinifera

“…The studies change in focus (e.g., leaf vs. root feeding, host plants), but they are all linked by effector function groups. The majority of grape phylloxera effector candidates were related to target host defense suppression either by the interference with early signal cascades (e.g., calreticulins, glucose dehydrogenases, heat shock proteins) or the counteracting of activated host defense mechanisms (e.g., peroxidases, peroxiredoxins) [ 40 , 41 , 42 , 43 , 44 ]. Other grape phylloxera effector candidates were thought to be functionally related to plant gall formation traits (calmodulins, calreticulins, and proteins with RING-type zinc finger, EF-hand, ankyrin repeat domains) and feed intake/digestion processes (e.g., carboxypeptidases, serine proteases, glucose dehydrogenases) [ 40 , 41 , 42 , 43 , 44 ].…”

“… T5C [ 42 , 78 ] Peroxidase, peroxidoredoxins H 2 O 2 /ROS detoxification Sfl L2/3 - T5C [ 42 ] * Protein disulfide isomerases, mucins Stylet sheath formation Sfl L2/3 - T5C [ 42 ] Proteins with RING-type zinc finger, EF-hand, ankyrin repeat domains Modulation of cellular growth/development processes, ETI signaling Pop, sfl L2/3/4 & A Frontenac, Harmony, V.arizonica , V.riparia Cab. Sauvignon, T5C [ 41 , 43 , 44 ] * RING-containing E3 ligases Interaction with cellulose biosynthesis ( VviCSLD5 ), protein translation ( VviRPS4B ) Pop L2/3/4 & A V. riparia − [ 41 ] …”

“…The first comparative transcriptome analysis published showed that root- and leaf-feeding grape phylloxera stages exhibit major intraspecific changes in transcriptomic profiles related to different lifestyles [ 40 ]. Studies analyzing genes underlying effector proteins [ 41 , 42 , 43 , 44 ] have been very useful in understanding the complexity of the grape phylloxera– Vitis interaction. As a cyclical parthenogenetic monophagous and gall-feeding insect that cohabitates with technologically altered host plants (grafts) in extremely diverse habitats (introduced and native), changes in performance and genetic structures among phylloxera populations are likely [ 26 , 45 , 46 ].…”

“…As a cyclical parthenogenetic monophagous and gall-feeding insect that cohabitates with technologically altered host plants (grafts) in extremely diverse habitats (introduced and native), changes in performance and genetic structures among phylloxera populations are likely [ 26 , 45 , 46 ]. Previously, transcriptomic and effector studies focused on feeding and developmental life stages [ 40 ], geographical or phylogenetic distribution [ 43 , 44 , 47 ], or genomic functional observations [ 41 , 42 ]. Newer studies on grape phylloxera feeding sites (leaf and root galls) show the massive impact on the metabolism of the host plants [ 10 , 13 , 48 ].…”