BACKGROUND: Rice blast, caused by Magnaporthe oryzae, is the most devastating disease in rice. Recently, trifloxystrobin was registered for the control of M. oryzae in China. The resistance profile and mechanism of M. oryzae to trifloxystrobin were investigated in the present study, providing important data for the recommended use of trifloxystrobin. RESULTS: The baseline sensitivity was established at a half maximal effective concentration (EC 50) of 0.024 ∼g mL −1. Nine stable trifloxystrobin-resistant mutants were generated with EC 50 values ranging from 12.75 to 171.49 ∼g mL −1. The mutants exhibited strong adaptive traits in sporulation, conidial germination, and pathogenicity. Positive cross-resistance was only observed between trifloxystrobin and azoxystrobin, but not between trifloxystrobin and carbendazim, isoprothiolane, prochloraz, or chlorothalonil. The point mutation G143S in cytochrome b (cyt b) protein was found in eight high-resistance mutants with resistant factor ranging from 2295.16 to 13 200.00; and the double mutation G137R/M296V only occurred in Mg117-1 with resistance factor ≈ 900. The G143S mutation weakened hydrogen bond interactions, and G137R/M296V changed the conformation of trifloxystrobin in the cyt b binding pocket. A molecular detection method was established for the rapid detection of G143S mutants in M. oryzae. CONCLUSION: The resistance risk of M. oryzae to trifloxystrobin could be moderate to high. Two genotypes with three pointmutations G143S, G137R, and M296V conferred resistance to trifloxystrobin in M. oryzae.
Summary Wheat stripe rust caused by the fungus Puccinia striiformis f. sp. tritici (Pst) is one of the most destructive wheat diseases resulting in significant losses to wheat production worldwide. The development of disease‐resistant varieties is the most economical and effective measure to control diseases. Altering the susceptibility genes that promote pathogen compatibility via CRISPR/Cas9‐mediated gene editing technology has become a new strategy for developing disease‐resistant wheat varieties. Calcineurin B‐like protein (CBL)‐interacting protein kinases (CIPKs) has been demonstrated to be involved in defence responses during plant‐pathogen interactions. However, whether wheat CIPK functions as susceptibility factor is still unclear. Here, we isolated a CIPK homoeologue gene TaCIPK14 from wheat. Knockdown of TaCIPK14 significantly increased wheat resistance to Pst, whereas overexpression of TaCIPK14 resulted in enhanced wheat susceptibility to Pst by decreasing different aspects of the defence response, including accumulation of ROS and expression of pathogenesis‐relative genes. We generated wheat Tacipk14 mutant plants by simultaneous modification of the three homoeologues of wheat TaCIPK14 via CRISPR/Cas9 technology. The Tacipk14 mutant lines expressed race‐nonspecific (RNS) broad‐spectrum resistance (BSR) to Pst. Moreover, no significant difference was found in agronomic yield traits between Tacipk14 mutant plants and Fielder control plants under greenhouse and field conditions. These results demonstrate that TaCIPK14 acts as an important susceptibility factor in wheat response to Pst, and knockout of TaCIPK14 represents a powerful strategy for generating new disease‐resistant wheat varieties with BSR to Pst.
Plant cell walls are composed of polysaccharides such as cellulose, hemicelluloses, and pectins, whose location and function differ depending on plant type. UDP‐Ara mutases (UAMs) have been reported to play important roles in plant development and response to various plant stresses (abiotic and biotic). However, little work has been reported on UAM in wheat. In this study, we dissected the role of the UAM family member, UAM3, during the interaction between wheat and the stripe rust fungus, Puccinia striiformis f. sp. tritici (Pst), and in response to treatment with salicylic acid (SA). RNA interference (RNAi)‐based stable silencing of TaUAM3 resulted in decreased resistance to Pst fungus. In addition, CRISPR‐mediated genome editing (GE) of TaUAM3 enhanced the susceptibility of wheat to Pst or compromised disease resistance accompanied by increased fungal growth and decreased H2O2 production in plant tissues. Moreover, the transcript levels of pathogenesis‐related (PR) genes and reactive oxygen species (ROS)‐generating genes were down‐regulated in both the RNAi‐silenced and CRISPR‐edited plants, while the ROS‐scavenging gene, TaCAT3, was up‐regulated. Therefore, TaUAM3 positively regulates the resistance of wheat to Pst.
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