Understanding molecular events during barley aphid interactions

Abstract

Aphids are phloem-feeding insects that cause severe yield losses on crops, including cereals such as barley. While most aphid species are limited to one or few host species, some are able to reproduce on many plants belonging to different families. Interestingly, aphid probing-behaviour can be observed on both host and non-host plants indicating that interactions take place at the molecular level and may impact host range.

We found that the barley specialist Rhopalosiphum padi and the broad host range Myzus persicae showed differences in colonization, settlement and probing-behaviour on barley. Analyses of barley transcriptional responses revealed gene sets differentially regulated upon the different barley-aphid interactions, where M. persicae induced the most pronounced barley transcriptional response. Interestingly, we identified several genes strongly up-regulated upon interaction with M. persicae, and to a lesser extent upon R. padi interaction, including thionins and the Late Embryogenesis Abundant gene 14 (LEA14). Ectopic expression of two barley thionins in Nicotiana benthamiana reduced host susceptibility to M. persicae, potentially reflecting a role in defence against aphids. We have generated barley mutant lines, using CRISPR-Cas9 technology, to investigate its role in plant-aphid interactions.

We characterized also the R. padi and M. persicae responses upon being exposed to different plant environments. We characterized the aphid probing and feeding in different host and poor-/non-host plants, revealing that plant resistance to aphids can be based in different plant cell layers. Aphids only showed limited transcriptional responses upon being moved from host plants to either a host-, poor-host/non-host plant, or to an artificial diet, and predicted aphid effector genes, essential for parasitism, were expressed regardless of the type of interaction.

Focusing on aphid effectors, we characterized 4 putative orthologous effector pairs from R. padi and M. persicae with regards to their subcellular localization, expression, and contribution to plant susceptibility. We demonstrate that ectopic expression of two R. padi effectors in barley enhances plant susceptibility to R. padi but not M. persicae, highlighting the importance of these two effectors in barley colonization in an aphid species-specific manner.

Date of Award	2018
Original language	English
Awarding Institution	University of Dundee
Supervisor	Jorunn Bos (Supervisor) & John Jones (Supervisor)