Exploring Immune Receptors: Recognizing and Resisting Pathogens in Plants

2023-07-06 06:30:13
-Establishment of resistance to various pathogens using immune receptors- □ Recognition of pathogens and formation of resistance by plant immune receptors o Unlike animals that have immune cells and adaptive immunity, plants have various types of immune receptors present in each cell to prevent pathogens recognizes and initiates an immune response. Pathogens secrete specific proteins, called effectors, into plant cells to inhibit various plant functions or manipulate them in favor of survival. In response, immune receptors present in plant cells recognize the effector secreted by the pathogen and trigger a strong immune response. o It has been reported that immune receptors indirectly recognize pathogens by detecting changes in bait proteins in plant cells when recognizing effectors. The most studied decoy protein is a protein called RIN4 found in the cruciferous plant Arabidopsis, and various bacterial effectors change RIN4 through post-translational modifications. The change is recognized by immune receptors called RPS2 and RPM1 and triggers an immune response. Bacterial effectors that induce an immune response in Arabidopsis have been reported to cause a strong immune response in tobacco, a plant of the Solanaceae family. However, recognition mechanisms for these effectors have not been studied in tobacco. □ Discovery of Ptr1 and ZAR1 recognizing various bacterial effectors o In this study, to investigate how bacterial effectors that change RIN4 in Arabidopsis thaliana are recognized in cigarettes, effector recognition for 300 known tobacco immune receptors was explored. Virus-induced gene silencing was used to screen many immune receptors in a fast and effective reverse genetics method. As a result, it was found that among the tobacco immune receptors, an immune receptor called Ptr1 recognizes the effectors AvrRpt2, AvrRpm1 and AvrB of the pathogen Pseudomonas. o Furthermore, it was found that the Pseudomonas effector HopZ5 and the Xanthomonas effector AvrBsT are also recognized by Ptr1, and that these effectors are additionally recognized by another immune receptor called ZAR1 in an independent mechanism. It was also reported that the intensity of the immune response caused by each receptor was different in tobacco and pepper. The important effector of Xanthomonas that causes bacterial spot in tomatoes and peppers is known as AvrBsT, and it was also confirmed that Ptr1 and ZAR1 recognize AvrBsT to form resistance to this pathogen. □ Convergent evolution of pathogen effector recognition in Arabidopsis and tobacco o In this study, effectors recognized in Arabidopsis thaliana were recognized by Ptr1 and ZAR1, which have no genetic similarity to Arabidopsis immune receptors RPS2 and RPM1, through convergent evolution in tobacco. reported to be Furthermore, the process in which various effectors in tobacco are recognized by one immune receptor Ptr1 seems to be a special recognition mechanism different from the previously reported recognition patterns of immune receptors and effectors. In the future, we plan to explore decoy proteins required for the recognition mechanism of Ptr1 and ZAR1 and proteins involved in immune response. Such studies will give a deeper understanding of how the two receptors form a broad effector recognition spectrum. It is expected that Ptr1 and ZAR1, which recognize various bacterial pathogens, will be utilized in solanaceous crops to greatly contribute to disease resistance and crop protection research. This study was supported by the National Research Foundation of Korea, the Center for Plant Immunity Research at Seoul National University, and the Rural Development Administration, and was published in New Phytologist, an internationally renowned journal.

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연  구  결  과 

Ptr1 and ZAR1 immune receptors confer overlapping and distinct bacterial pathogen effector specificities 

Ye Jin Ahn*, Haseong Kim*, Sera Choi*, Carolina Mazo-Molina, Maxim Prokchorchik, Ning Zhang, Boyoung Kim, Hyunggon Mang, Naio Koehler, Jieun Kim, Soeui Lee, Hayeon Yoon, Doil Choi, Min-Sung Kim, Cécile Segonzac, Gregory B. Martin§, Alex Schultink§, and Kee Hoon Sohn§ 
(New Phytologist;

● Some nucleotide-binding and leucine-rich repeat receptors (NLRs) indirectly detect pathogen effectors by monitoring their host targets. In Arabidopsis thaliana, RIN4 is targeted by multiple sequence-unrelated effectors and activates immune responses mediated by RPM1 and RPS2.  These effectors trigger cell death in Nicotiana benthamiana, but the corresponding NLRs have yet not been identified. To identify N. benthamiana NLRs (NbNLRs) that recognize Arabidopsis RIN4-targeting effectors, we conducted a rapid reverse genetic screen using an NbNLR VIGS library.
● We identified that the N. benthamiana homolog of Ptr1 (Pseudomonas tomato race 1) recognizes the Pseudomonas effectors AvrRpt2, AvrRpm1, and AvrB. 
● We demonstrated that recognition of the Xanthomonas effector AvrBsT and the Pseudomonas effector HopZ5 is conferred independently by the N. benthamiana homolog of Ptr1 and ZAR1. Interestingly, the recognition of HopZ5 and AvrBsT is contributed unequally by Ptr1 and ZAR1 in N. benthamiana and Capsicum annuum. In addition, we showed that the RLCK XII family protein JIM2 is required for the NbZAR1-dependent recognition of AvrBsT and HopZ5.
● The recognition of sequence-unrelated effectors by NbPtr1 and NbZAR1 provides an additional example of convergently evolved effector recognition. Identification of key components involved in Ptr1 and ZAR1-mediated immunity could reveal unique mechanisms of expanded effector recognition. 

● 식물의 면역 수용체 nucleotide-binding and leucine-rich repeat receptor (NLR)은 병원체의 이펙터 (effector)가 표적으로 삼는 식물 세포 내의 단백질의 감지해서 이펙터를 간접적으로 인식한다. 애기장대에서는 RIN4라는 단백질이 유전자적 유사성이 없는 여러 이펙터에 의해서 번역 후 변형(post-translational modification)이 일어나고 이 변화는 RPM1과 RPS2 면역 수용체를 통한 면역 반응을 활성화한다. 애기장대 RIN4를 타겟하는 이펙터들은 담배에서도 세포사멸반응을 동반한 면역반응을 일으키는데 아직 이 이펙터들을 인식하는 담배의 면역 수용체는 연구되지 않았다. 애기장대 RIN4를 타겟하는 이펙터를 인식하는 담배 면역 수용체를 탐색하기 위해서 역유전학적 방법으로 설계된 NbNLR VIGS library를 이용하였다.
● 그 결과 야생 토마토에서 발견된 Ptr1 (Pseudomonas tomato race 1)과 상동되는 NbPtr1 (Nicotiana benthamiana homolog of Ptr1)가 Pseudomonas 이펙터 AvrRpt2, AvrRpm1, 그리고 AvrB를 인식하는 것을 발견했다.
● Xanthomonas 이펙터 AvrBsT와 Pseudomonas 이펙터 HopZ5은 NbPtr1과 NbZAR1에 의해서 독립적인 기작으로 인식되는 것을 확인했다. 더 흥미로웠던 사실은 담배와 고추에서 HopZ5와 AvrBsT의 인식과 면역반응의 강도가 각 면역 수용체 Ptr1과 ZAR1에 의해서 다르게 나타난다는 점이었다. 그리고 receptor-like cytoplasmic kinase XII 단백질인 JIM2는 NbZAR1이 HopZ5와 AvrBsT를 인식할 때 필요하다는 것도 보여주었다.
● 유전자적으로 유사성이 없는 병원체 이펙터를 인식하는 NbPtr1과 NbZAR1은 이펙터의 인식이 다양한 식물 종에서 수렴적으로 진화된 것을 보여준다. Ptr1과 ZAR1의 면역 활성 기작에 기여하는 중요 단백질에 대한 연구는 면역 수용체의 이펙터 인식 확장에 대한 기작을 이해하는 데 중요할 것으로 예상된다.
 

애기장대와 담배에서 병원체 이펙터 인식의 수렴적 진화
애기장대와 담배에서 Pseudomonas 이펙터 AvrRpt2, AvrB, AvrRpm1, 그리고 HopZ5와 Xanthomonas 이펙터 AvrBsT를 인식하는 면역 수용체와 인식 과정에 차이를 정리하였다. 애기장대에서는 다섯 개의 이펙터가 RIN4라는 단백질을 번역 후 변화(post-translational modification)를 시키고 RIN4의 변화는 RPM1과 RPS2에 의해서 감지가 되어 면역반응이 일어난다. 그에 반해 담배에서는 하나의 면역 수용체 Ptr1이 다섯 개의 이펙터를 인식하고 HopZ5와 AvrBsT은 ZAR1에 의해서 독립적인 기작으로 추가 인식이 된다. ZAR1의 면역 활성에는 JIM2라는 식물 세포 내의 RLCK XII family 단백질이 필요한 것으로 확인된다.
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#Investigation #plant #immunity #activation #mechanism #disease #resistance #protein #recognizes #bacterial #pathogens #BRIC

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