Rapid screening for citrus canker resistance employing pathogen-associated molecular pattern-triggered immunity responses.

Marco Pitino,Yongping Duan,Cheryl M Armstrong

doi:10.1038/hortres.2015.42

Marco Pitino, Yongping Duan + Show 1 more

Open Access

https://doi.org/10.1038/hortres.2015.42

Copy DOI

Journal: Horticulture research	Publication Date: Sep 9, 2015
Citations: 28	License type: CC BY-NC-ND 4.0

Abstract

Citrus canker, caused by the bacterial pathogen Xanthomonas citri ssp. citri (Xcc), has been attributed to millions of dollars in loss or damage to commercial citrus crops in subtropical production areas of the world. Since identification of resistant plants is one of the most effective methods of disease management, the ability to screen for resistant seedlings plays a key role in the production of a long-term solution to canker. Here, an inverse correlation between reactive oxygen species (ROS) production by the plant and the ability of Xcc to grow and form lesions on infected plants is reported. Based on this information, a novel screening method that can rapidly identify citrus seedlings that are less susceptible to early infection by Xcc was devised by measuring ROS accumulation triggered by a 22-amino acid sequence of the conserved N-terminal part of flagellin (flg22) from X. citri ssp. citri (Xcc-flg22). In addition to limiting disease symptoms, ROS production was also correlated with the expression of basal defense-related genes such as the pattern recognition receptors LRR8 and FLS2, the leucine-rich repeat receptor-like protein RLP12, and the defense-related gene PR1, indicating an important role for pathogen-associated molecular pattern-triggered immunity (PTI) in determining resistance to citrus canker. Moreover, the differential expression patterns observed amongst the citrus seedlings demonstrated the existence of genetic variations in the PTI response among citrus species/varieties.

Highlights

Asiatic citrus canker (ACC) is caused by the gram-negative bacterial pathogen Xanthomonas citri ssp. citri (Xcc), which is the most virulent bacteria that cause citrus canker and the one with the widest host range.[1,2] For most citrus species, ACC is a devastating disease, resulting in extensive damage to commercial citrus cultivars in subtropical production areas of the world.[3]
Production of reactive oxygen species (ROS) triggered by Xcc-flg[22] varies among seedlings from various citrus species One of the earliest cellular responses following successful pathogen recognition, known as the oxidative burst, is characterized by a rapid and transient accumulation of ROS.[45,46]. This response can be induced during pathogen invasion or via elicitor treatment such as that triggered by the perception of the flagellin peptide flg22.47 To trigger ROS production in our seedlings collection, we used the flagellin peptide from X. citri (Xcc-flg22)
The photon counts per second (CPS) for seedlings within a species oscillated around an average specific for that particular species, which ranged from 101 to 509 depending upon the species

Summary

Introduction

Asiatic citrus canker (ACC) is caused by the gram-negative bacterial pathogen Xanthomonas citri ssp. citri (Xcc) (reclassified from ‘A’ pathotype Xanthomonas axonopodis pv. citri), which is the most virulent bacteria that cause citrus canker and the one with the widest host range.[1,2] For most citrus species, ACC is a devastating disease, resulting in extensive damage to commercial citrus cultivars in subtropical production areas of the world.[3]. Asiatic citrus canker (ACC) is caused by the gram-negative bacterial pathogen Xanthomonas citri ssp. The bacteria remain alive in the margins of the lesions on the leaves and fruits until they fall[4] with older lesions taking on a crater-like appearance.[7] The bacterium multiplies to a high level in the lesions, which disperses to new growth and other plants when free moisture is present.[8,9,10] Rain and wind increase its dispersal,[11] while extreme weather conditions such as hurricanes and tropical storms are associated with longdistance dissemination and a local increase the level of disease.[12] Insect feeding can lead to significant field infections. It has been noted that the Asiatic citrus leafminer (Phyllocnists citrella) damages citrus by feeding on new leaf growth and by greatly exacerbating the severity of citrus canker.[13,14]

Methods

Results

Conclusion