Characterization of the role of the Parastagonospora nodorum effector SnTox267 in virulence on wheat using confocal microscopy

Authors: NELSON, ASHLEY - North Dakota State University; KARIYAWASAM, GAYAN - North Dakota State University; SENEVIRATNE, SUDESHI - North Dakota State University; BOROWICZ, PAWEL - North Dakota State University; Faris, Justin; LIU, ZHAOHUI - North Dakota State University; Friesen, Timothy

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/9/2021
Publication Date: 3/15/2022
Citation: Nelson, A.C., Kariyawasam, G.K., Seneviratne, S., Borowicz, P., Faris, J.D., Liu, Z., Friesen, T.L. 2022. Characterization of the role of the Parastagonospora nodorum effector SnTox267 in virulence on wheat using confocal microscopy. In: Fungal Genetics Conference, March 15-20, 2022, Pacific Grove, CA.

Interpretive Summary:

Technical Abstract: Parastagonospora nodorum is an economically important fungal pathogen that causes septoria nodorum blotch (SNB), a foliar disease on wheat. P. nodorum is known to secrete necrotrophic effectors that aid in the manipulation of the plant immune system, resulting in necrotrophic effector triggered susceptibility (NETS). Necrotrophic effectors SnToxA, SnTox1, SnTox3, SnTox5 and SnTox267 have been validated and functionally characterized, and have been shown to be involved in triggering of the oxidative burst and programmed cell death, PR gene upregulation, chitin binding, binding to PR proteins and/or facilitating colonization of the host. SnTox267 was recently shown to target at least two independent pathways involving host genes Snn2, Snn6, and Snn7. However, apart from induction of PCD, the function of SnTox267 is not well characterized. In this study we used confocal microscopy to observe the role that SnTox267 plays in plant colonization. We compared Sn79-1087, an avirulent isolate of P. nodorum, and Sn79+SnTox267, an Sn79-1087 strain transformed with SnTox267, both tagged with red fluorescent protein (RFP) to identify differences in germination, penetration, and colonization of the leaf. Infection was evaluated at 4, 12, 24, 48, 72, 96 and 120 hours post inoculation (HPI) in three different wheat lines including BR34 (snn2Snn6; SnTox267-insensitive), BG223 (Snn2Snn6; SnTox267-sensitive), and ITMI37 (Snn2Snn6; SnTox267-sensitive). In the compatible interaction (Sn79+Tox267 on BG223 or ITMI37), spores germinated by 4 hpi and fungal penetration of the leaf began between 12hpi and 24hpi with substantial colonization of the epidermis being complete at 48hpi. The colonization of the mesophyll began at 48hpi and continued through 72hpi without visible cell death. Host cellular disruption began at 96hpi and increased in severity with complete cell death adjacent to mycelia by 120hpi. The incompatible interaction (Sn79-1087 on BG223 or ITMI37) by comparison showed similar germination, penetration, and colonization of the epidermis by 48hpi but did not progress beyond the epidermal layer of the leaf and never induced significant cell death. The incompatible interaction involving BR34 did not show any colonization of the mesophyll by 120h in either the 79-1087 or 79+Tox267 interactions. Collectively, these preliminary experiments suggest that SnTox267 facilitates colonization of the mesophyll by targeting the Snn2/Snn6 pathway ultimately resulting in cell death.