Maize and wheat independently evolved the capacity to control plant defenses through O-methylation of regulatory benzoxazinoids.

Sieve tubes are transport conduits not only for photoassimilates but also for macromolecules and other compounds that are involved in sieve tube maintenance and systemic signalling. In order to gain sufficient amounts of pure phloem exudates from barley plants for analyses of the protein and mRNA composition, a previously described stylectomy set-up was optimized. Aphids were placed in sealed cages, which, immediately after microcauterization of the stylets, were flooded with water-saturated silicon oil. The exuding phloem sap was collected with a capillary connected to a pump. Using up to 30 plants and 600 aphids (Rhopalosiphum padi) in parallel, an average of 10 μl of phloem sap could be obtained within 6 h of sampling. In first analyses of the macromolecular content, eight so far unknown phloem mRNAs were identified by cDNA-amplified fragment length polymorphism. Transcripts in barley phloem exudates are related to metabolism, signalling, and pathogen defence, for example coding for a protein kinase and a pathogen- and insect-responsive WIR1A (wheat-induced resistance 1A)-like protein. Further, one-dimensional gel electrophoresis and subsequent partial sequencing by mass spectrometry led to the identification of seven major proteins with putative functions in stress responses and transport of mRNAs, proteins, and sugars. Two of the discovered proteins probably represent isoforms of a new phloem-mobile sucrose transporter. Notably, two-dimensional electrophoresis confirmed that there are >250 phloem proteins awaiting identification in future studies.

Background: Small (s) RNA molecules are crucial factors in the communication between hosts and their interacting pathogens/pests that can modulate both host defense and microbial virulence/pathogenicity known as crosskingdom RNA interference (ckRNAi). Consistent with this, sRNAs and their double-stranded (ds) RNA precursors have been adopted to control plant diseases through exogenously applied RNA biopesticides, known as spray-induced gene silencing (SIGS). While RNA spray proved to be effective, the mechanisms underlying the transfer and uptake of SIGS-associated RNAs are inadequately understood. Moreover, the use of the SIGS-technology as a biopesticide will require the systemic spreading of dsRNA/siRNA signals.Results: The integration of our findings strongly support the notion of long-distance spreading of SIGS-associated dsRNA and/or siRNA. In summary, our findings support the model that SIGS involves: (i) uptake of sprayed dsRNA by the plant (via stomata); (ii) transfer of apoplastic dsRNAs into the symplast (DCL processing into siRNAs); (iii) systemic translocation of siRNA or unprocessed dsRNA via the vascular system (phloem/xylem); (iv) uptake of apoplastic dsRNA or symplastic dsRNA/siRNA depending on the lifestyle/feeding behavior of the pathogen/pest. Conclusions:Our findings are significant contributions to our mechanistic understanding of RNA spray technology, as our previous data indicate that SIGS requires the processing of dsRNAs by the fungal RNAi machinery.

Although sessile, plants are able to grow toward or away from an environmental stimulus. Important examples are stem or leaf orientation of higher plants in response to the direction of the incident light. The responsible photoreceptors belong to the phototropin photoreceptor family. Although the mode of phototropin action is quite well understood, much less is known of how the light signal is transformed into a bending response. Several lines of evidence indicate that a lateral auxin gradient is responsible for asymmetric cell elongation along the light gradient within the stem. However, some of the molecular key players leading to this asymmetric auxin distribution are, as yet, unidentified. Previously, it was shown that phototropin gets autophosphorylated upon illumination and binds to a scaffold protein termed NPH3 (for nonphototropic hypocotyl 3). Using a yeast three-hybrid approach with phototropin and NPH3 as a bait complex, we isolated a protein, termed EHB1 (for enhanced bending 1), with a so far unknown function, which binds to this binary complex. This novel interacting factor negatively affects hypocotyl bending under blue light conditions in Arabidopsis (Arabidopsis thaliana) and thus seems to be an important component regulating phototropism. Interestingly, it could be shown that the gravitropic response was also affected. Thus, it cannot be ruled out that this protein might also have a more general role in auxin-mediated bending toward an environmental stimulus.

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1 7 Highlight 1 8The use of the SIGS-technology as a biopesticide will require the systemic spreading of 1 9 dsRNA/siRNA signals. Our findings strongly support the notion of phloem-mediated long-2 0 distance movement of SIGS-associated RNAs. Abstract 2 2 Small (s)RNA molecules are crucial factors in the communication between hosts and their 2 3 3 1 distance movement of SIGS-associated dsRNA and/or siRNA. These findings are significant 3 2 contributions to our mechanistic understanding of RNA spray technology, as our previous 3 3 data indicate that SIGS requires the processing of dsRNAs by the fungal RNAi machinery. In 3 4 summary, our findings support the model that SIGS involves: (i) uptake of sprayed dsRNA by 3 5 the plant (via stomata); (ii) transfer of apoplastic dsRNAs into the symplast (DCL processing 3 6 into siRNAs); (iii) systemic translocation of siRNA or unprocessed dsRNA via the vascular 3 7 system (phloem/xylem); (iv) uptake of apoplastic dsRNA or symplastic dsRNA/siRNA 3 8 depending on the lifestyle/feeding behavior of the pathogen/pest.3 9

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