Transcriptional changes in the aphid species Myzus cerasi under different host and environmental conditions.

Aphids feature complex life cycles, which in the case of many agriculturally important species involve primary and secondary host plant species. Whilst host alternation between primary and secondary host can occur in the field depending on host availability and the environment, aphid populations maintained as laboratory stocks generally are kept under conditions that allow asexual reproduction by parthenogenesis on secondary hosts. We used Myzus cerasi (black cherry aphid) to assess aphid transcriptional differences between populations collected from primary hosts in the field and those adapted to secondary hosts under controlled environment conditions. Transfer of M. cerasi collected from local cherry trees to reported secondary host species resulted in low survival rates. Moreover, aphids were unable to survive on the secondary host land cress, unless first adapted to another secondary host, cleavers. Transcriptome analyses of the different aphid populations (field collected and adapted) revealed extensive transcriptional plasticity to a change in environment, with predominantly genes involved in redox reactions differentially regulated. Most of the differentially expressed genes were duplicated and we found evidence for differential exon usage. Our data suggest that aphid adaptation to different environments may pose a major hurdle and leads to extensive gene expression changes.

Barley transcriptome analyses upon interaction with different aphid species identify thionins contributing to resistance.

Aphids are phloem-feeding insects that cause yield loss on a wide range of crops, including cereals such as barley. Whilst 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 species, indicating that interactions take place at the molecular level that may impact host range. Here, we aimed to gain insight into the interaction of barley with aphid species differing in their ability to infest this crop by analysing transcriptional responses. Firstly, we determined colonization efficiency, settlement and probing behaviour for the aphid species Rhopalosiphum padi, Myzus persicae and Myzus cerasi, which defined host, poor-host and non-host interactions, respectively. Analyses of barley transcriptional responses revealed gene sets differentially regulated upon the different barley-aphid interactions and showed that the poor-host interaction with M. persicae resulted in the strongest regulation of genes. Interestingly, we identified several thionin genes strongly up-regulated upon interaction with M. persicae, and to a lesser extent upon R. padi interaction. Ectopic expression of two of these genes in Nicotiana benthamiana reduced host susceptibility to M. persicae, indicating that thionins contribute to defences against aphids.

Systemic Modulation of Gene Expression in Tomato by Trichoderma hamatum 382.

ABSTRACT A light sphagnum peat mix inoculated with Trichoderma hamatum 382 consistently provided a significant (P = 0.05) degree of protection against bacterial spot of tomato and its pathogen Xanthomonas euvesicatoria 110c compared with the control peat mix, even though this biocontrol agent did not colonize aboveground plant parts. To gain insight into the mechanism by which T. hamatum 382 induced resistance in tomato, high-density oligonucleotide microarrays were used to determine its effect on the expression pattern of 15,925 genes in leaves just before they were inoculated with the pathogen. T. hamatum 382 consistently modulated the expression of genes in tomato leaves. We identified 45 genes to be differentially expressed across the replicated treatments, and 41 of these genes could be assigned to at least one of seven functional categories. T. hamatum 382-induced genes have functions associated with biotic or abiotic stress, as well as RNA, DNA, and protein metabolism. Four extensin and extensin-like proteins were induced. However, besides pathogenesis-related protein 5, the main markers of systemic acquired resistance were not significantly induced. This work showed that T. hamatum 382 actively induces systemic changes in plant physiology and disease resistance through systemic modulation of the expression of stress and metabolism genes.