Upon immune activation, chloroplasts switch off photosynthesis, produce antimicrobial compounds and associate with the nucleus through tubular extensions called stromules. Although it is well established that chloroplasts alter their position in response to light, little is known about the dynamics of chloroplast movement in response to pathogen attack. Here, we report that during infection with the Irish potato famine pathogen Phytophthora infestans, chloroplasts accumulate at the pathogen interface, associating with the specialized membrane that engulfs the pathogen haustorium. The chemical inhibition of actin polymerization reduces the accumulation of chloroplasts at pathogen haustoria, suggesting that this process is partially dependent on the actin cytoskeleton. However, chloroplast accumulation at haustoria does not necessarily rely on movement of the nucleus to this interface and is not affected by light conditions. Stromules are typically induced during infection, embracing haustoria and facilitating chloroplast interactions, to form dynamic organelle clusters. We found that infection-triggered stromule formation relies on BRASSI-NOSTEROID INSENSITIVE 1-ASSOCIATED KINASE 1 (BAK1)-mediated surface immune signaling, whereas chloroplast repositioning towards haustoria does not. Consistent with the defense-related induction of stromules, effector-mediated suppression of BAK1-mediated immune signaling reduced stromule formation during infection. On the other hand, immune recognition of the same effector stimulated stromules, presumably via a different pathway. These findings implicate chloroplasts in a polarized response upon pathogen attack and point to more complex functions of these organelles in plant-pathogen interactions.

Influenza is an acute respiratory infection disease caused by the influenza virus. At present, due to the high mutation rate of influenza virus, it is difficult for the existing antiviral drugs to play an effective antiviral effect continually, so it is urgent to develop a new anti-influenza drug. Recently, more and more studies have been conducted on the antiviral activity of Astragalus membranaceus, but the specific antiviral mechanism of this traditional Chinese medicine is not clear. In this study, the results proved that the Astragalus membranaceus injection showed obvious anti-influenza virus activity. It could improve the survival rate of Raw264.7 cells which were infected with influenza virus, while it improved the blocking effect of influenza virus on cell cycle after infection, increased the SOD activity, and reduced the MDA content. At the same time, the innate immunity was affected by regulating the expression of TLR3, TAK1, TBK1, IRF3, and IFN-β in the TLR3-mediated signaling pathway, thus exerting its antiviral effect in vitro.

No abstract

Chloroplasts are light harvesting organelles that arose from ancient 20 endosymbiotic cyanobacteria. Upon immune activation, chloroplasts switch off 21 photosynthesis, produce anti-microbial compounds, and develop tubular 22 65 development relies on surface immune signalling, whereas the pathogen subverts this 66 remotely by switching off surface immune pulses. These results implicate chloroplast 67 photo-relocation machinery in plant focal immune responses and demonstrate that 68 chloroplasts play a direct role in antagonizing pathogen invasion.69 Results & Discussion: 70 To gain insights into defence-related chloroplast functions, we investigated chloroplast 71 dynamics during P. infestans infection of the solanaceous model plant Nicotiana 72 benthamiana. Confocal microscopy of infected leaf epidermal cells stably expressing 73 GFP in chloroplast stroma (CpGFP hereafter) revealed that chloroplasts accumulate at 74 58% of haustoria (n = 299 haustoria) (Fig. 1A-C). Notably, chloroplasts are mainly 75 positioned around infection sites, sieging haustoria in a highly dynamic fashion (Fig. 1C, 761E and Movie S1-3). Furthermore, compared to non-infected controls, we recorded a 5-77 fold increase in stromule formation in infected CpGFP cells ( Fig. 1A-B, 1D). Notably, 78 chloroplasts seized haustoria, tightly embracing the EHM through stromules that extend 79 and coil around the pathogen (Fig. 1A, 1C, Movie S3). Expression of the EHM marker 80 protein RFP:REM1.3 (Bozkurt et al., 2014) in infected CpGFP plants, allowed us to 81 collect further evidence that chloroplasts intimately associate with the EHM (Fig. S1, 82Movie S4). Remarkably, time lapse-microscopy showed that chloroplasts plunge towards 83 haustoria and embrace the EHM following haustorial penetration (Fig. 1E, Movie S5, Fig. 84 S2), suggesting that chloroplasts may participate in focal immunity. 85To determine the extent to which chloroplasts physically associate with the EHM, we 86 next employed optical tweezers in combination with Total Internal Fluorescence 87 Microscopy (TIRF) in infected CpGFP plants. Using optical tweezers, we successfully 88 trapped and moved 17% of chloroplasts (n = 29) in non-haustoriated cells, a distance 89 greater than the 10 μm threshold. In comparison, we were unable to trap and move any 90 chloroplasts (0%, n = 18) neighbouring haustoria past the threshold, indicating a strong 91 association between the chloroplasts and the EHM. Consistent with this, we recorded a 92 few instances where these chloroplasts were initially pulled away from the EHM, but 93 before they passed the distance threshold they escaped the trap and sprang back 94 towards their former position (22%, n = 18) ( Fig. 1G, Movie S6). Taken together, these 95 results demonstrate that chloroplasts mobilize towards haustoria and tightly embrace the 96 EHM through induction of stromules, possibly to increase the surface area of interaction, 97 in a manner similar to chloroplast-nucleus communication upon activation of antiviral 98 immunity (Kumar et al., 2018).

No abstract