Abstract
Aphids secrete diverse repertoires of effectors into their hosts to promote the infestation process. While 'omics' approaches facilitated the identification and comparison of effector repertoires from a number of aphid species, the functional characterization of these proteins has been limited to dicot (model) plants. The bird cherry-oat aphid Rhopalosiphum padi is a pest of cereal crops, including barley. Here, we extend efforts to characterize aphid effectors with regard to their role in promoting susceptibility to the R. padi-barley interaction. We selected three R. padi effectors based on sequence similarity to previously characterized Myzus persicae effectors and assessed their subcellular localization, expression, and role in promoting plant susceptibility. Expression of R. padi effectors RpC002 and Rp1 in transgenic barley lines enhanced plant susceptibility to R. padi but not M. persicae, for which barley is a poor host. Characterization of Rp1 transgenic barley lines revealed reduced gene expression of plant hormone signalling genes relevant to plant-aphid interactions, indicating that this effector enhances susceptibility by suppressing plant defences in barley. Our data suggest that some aphid effectors specifically function when expressed in host species, and feature activities that benefit their corresponding aphid species.
Highlights
Similar to plant pathogens, aphids form close associations with their hosts and secrete effector molecules to modulate host cell processes to their benefit
Aphid effector characterization efforts to date have focused on dicot plant species including Arabidopsis, tomato, and Nicotiana benthamiana (Atamian et al, 2013; Bos et al, 2010; Chaudhary et al, 2019; Elzinga et al, 2014; Mutti et al, 2008; Pitino et al, 2011; Pitino and Hogenhout, 2013; Rodriguez et al, 2017; Rodriguez et al, 2014), and have not yet been described for monocot crops
It is crucial to understand the mechanisms employed by aphids and other t insects to infest cereals, as well as to gain insight into how aphid effector function may ip have diverged across different plant-aphid species interactions
Summary
Aphids form close associations with their hosts and secrete effector molecules to modulate host cell processes to their benefit. Functional characterization of aphid a effectors increased our understanding of how these proteins may function to enhance M plant susceptibility during infestation (as reviewed by (Yates and Michel, 2018) and (Nalam et al, 2019)), and pointed to host-specific effector activities (Elzinga et al, 2014; Pitino d and Hogenhout, 2013; Rodriguez et al, 2017). While expression of c MpC002 (M. persicae C002) in host species Arabidopsis and N. benthamiana enhances Ac susceptibility to M. persicae, expression of ApC002 from A. pisum in these same plant species has no visible impact on the host interaction with M. persicae (Pitino and Hogenhout, 2013). Several effectors from the broad host range pest M. persicae have been implicated in promoting host susceptibility, including Mp1 and Mp58 (Elzinga et al, 2014; Pitino and Hogenhout, 2013; Rodriguez et al, 2017). The Mp58-like effector from M M. euphorbiae ( called Me10) enhances tomato and N. benthamiana susceptibility to
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