Symptomatic plant viroid infections in phytopathogenic fungi
Authors: Hideki Kondo
Hongsheng Zhou
Qian Liu
Ruiling Bian
Liying Sun
Tianxing Pang
Shuang Wei
Xili Liu
Liu Yang
Erbo Niu
Ida Bagus Andika
Ziqian Lian
Yunfeng Wu
Journal: Proceedings of the National Academy of Sciences of the United States of America (2019)
Discipline: Multidisciplinary
Keywords: fungus; pathogenicity; plant viroid; transmission.
Affiliations: State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F University, 712100 Yangling, China., College of Plant Health and Medicine, Qingdao Agricultural University, 266109 Qingdao, China., Institute of Plant Science and Resources (IPSR), Okayama University, 710-0046 Kurashiki, Japan., State Key Laboratory of Crop Stress Biology for Arid Areas, College of Plant Protection, Northwest A&F University, 712100 Yangling, China; .

Abstract:  Viroids are pathogenic agents that have a small, circular noncoding RNA genome. They have been found only in plant species; therefore, their infectivity and pathogenicity in other organisms remain largely unexplored. In this study, we investigate whether plant viroids can replicate and induce symptoms in filamentous fungi. Seven plant viroids representing viroid groups that replicate in either the nucleus or chloroplast of plant cells were inoculated to three plant pathogenic fungi, Cryphonectria parasitica, Valsa mali, and Fusarium graminearum By transfection of fungal spheroplasts with viroid RNA transcripts, each of the three, hop stunt viroid (HSVd), iresine 1 viroid, and avocado sunblotch viroid, can stably replicate in at least one of those fungi. The viroids are horizontally transmitted through hyphal anastomosis and vertically through conidia. HSVd infection severely debilitates the growth of V. mali but not that of the other two fungi, while in F. graminearum and C. parasitica, with deletion of dicer-like genes, the primary components of the RNA-silencing pathway, HSVd accumulation increases. We further demonstrate that HSVd can be bidirectionally transferred between F. graminearum and plants during infection. The viroids also efficiently infect fungi and induce disease symptoms when the viroid RNAs are exogenously applied to the fungal mycelia. These findings enhance our understanding of viroid replication, host range, and pathogenicity, and of their potential spread to other organisms in nature. 

Retracted: No

PubPeer comments:
 How it can be possible that a viroid that replicates in the chloroplast, does it on a fungus that has no chloroplast?? , 
 Honestly, I do not trust their approach. RNA blot is the standard way to detect Viroid. RT-PCR is unacceptable because it yield false positive results. In this field nobody accepts RT-PCR for the detection of viroid. Based on my knowledge may labs have tried to infect fugues, yeast, or even animal cells with viroid, note of these labs succeed. , 
 #2 Researchers have request their reponses. In the response letter, the author did not provide an alternative approach. RNA blot is not a slower approach compared to RT-qPCR. In effect, RNA blot is faster, more accurate and, the only standard approach to detect Viroids. https: www.pnas.org content 117 19 10129.short ,