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Title: A single-nuclerotide deletion in the transcription factor gene Bcsmr1 causes formation of orange-colored sclerotia in Botrytis cinerea

item ZHOU, YINGJUN - Huazhong Agricultural University
item YANG, LONG - Huazhong Agricultural University
item WU, MINGDE - Huazhong Agricultural University
item Chen, Weidong
item LI, GUOQING - Huazhong Agricultural University
item ZHANG, JING - Huazhong Agricultural University

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2017
Publication Date: 12/12/2017
Citation: Zhou, Y., Yang, L., Wu, M., Chen, W., Li, G., Zhang, J. 2017. A single-nuclerotide deletion in the transcription factor gene Bcsmr1 causes formation of orange-colored sclerotia in Botrytis cinerea. Frontiers in Microbiology. 8:2492.

Interpretive Summary: Sclerotium is an important survival structure of a number of plant pathogenic fungi such as Sclerotinia spp. and Botrytis spp. Sclerotium enables pathogens to survive adverse conditions and either directly or indirectly provide inoculum for disease development in the next growing season. Melanin production and deposition on sclerotia is critical for the maturation and function of sclerotia. Understanding the molecular mechanisms of melanin biosynthesis and deposition will provide a better understanding of the process of sclerotial formation. Naturally occurring orange-colored sclerotial isolates of Botrytis cinerea were investigated in comparison with normal black-colored sclerotial isolates to unravel the process of sclerotial melanogenesis. It was found that a single nucleotide deletion in the transcription factor Bcsmr1 created a premature stop codon that resulted in a truncated protein. The truncated protein lost efficiency in transcribing melanogenesis-related genes, resulting in orange-colored sclerotia instead of normal black-colored sclerotia. Orange-colored sclerotia are less able to survive adverse conditions than black-colored sclerotia. This study confirmed the function of the gene Bcsmr1 for sclerotial melanogenesis, and also provided the first example of a single nucleotide mutation in Botrytis cinerea.

Technical Abstract: Botrytis cinerea (Bc) usually produces black-colored sclerotia (BS) due to deposition of DHN-melanin in sclerotial melanogenesis (SM). Our previous study reported six Bc isolates producing orange-colored sclerotia (OS) with SM deficiency. This study was done to unravel the molecular mechanism for the SM deficiency in OS isolates. We found that five SM genes (Bcpks12, Bcygh1, Bcbrn1/2, Bcscd1) were down-regulated in OS, compared to the genes in BS. However, the SM-regulatory gene Bcsmr1 had similar expression in both types of sclerotia, suggesting the SM deficiency is not due to lack of expression of Bcsmr1, but due to loss-of-function of Bcsmr1. Therefore, we cloned the Bcsmr1 gene from OS (Bcsmr1OS) and BS (Bcsmr1BS) isolates, and found a single-nucleotide deletion (SND) in Bcsmr1OS. The SND caused formation of a premature stop codon in the ORF of Bcsmr1OS, resulting in production of a 465-aa truncated protein. The transcription activation activity of the truncated protein was greatly reduced, compared to that of the 935-aa full-length protein encoded by Bcsmr1BS from the BS isolates. The loss-of-function of Bcsmr1OS was complemented by Bcsmr1BS. This study confirmed the regulatory function of Bcsmr1 for SM. It also provided the first case of SND-mediated mutation in Bc.