CRISPR/Cas9-Mediated SlMYC2 Mutagenesis Adverse to Tomato Plant Growth and MeJA-Induced Fruit Resistance to Botrytis cinerea

Abstract

Methyl jasmonate (MeJA), a natural phytohormone, played a critical role not only in plant growth but also in plant defense response to biotic and abiotic stresses. MYC2, a basic helix–loop–helix transcription factor, is a master regulator in MeJA signaling pathway. In the present work, slmyc2 mutants were generated by the clustered regularly interspaced short palindromic repeats and associated Cas9 protein (CRISPR/Cas9) system to investigate the role of SlMYC2 in tomato plant growth and fruit disease resistance induced by exogenous MeJA. The results showed that slmyc2 mutants possessed a higher number of flowers and a lower fruit setting rate in comparison with wild-type plants. In addition, the fruit shape of slmyc2 mutant was prolate, while the control fruits were oblate. Knockout of SlMYC2 significantly decreased the activities of disease defensive and antioxidant enzymes, as well as the expression levels of pathogen-related (PR) genes (SlPR-1 and SlPR-STH2) and the key genes related to jasmonic acid (JA) biosynthesis and signaling pathway including allene oxide cyclase (SlAOC), lipoxygenase D (SlLOXD), SlMYC2, and coronatine insensitive 1 (SlCOI1), and consequently aggravated the disease symptoms. By contrast, the disease symptoms were largely reduced in MeJA-treated fruit that possessed higher activities of these enzymes and expression levels of genes. However, the induction effects of MeJA on fruit disease resistance and these enzymes’ activities and genes’ expressions were significantly attenuated by knockout of SlMYC2. Therefore, the results indicated that SlMYC2 played positive regulatory roles not only in the growth of tomato plants but also in MeJA-induced disease resistance and the antioxidant process in tomato fruits.

Classification of CRISPR/Cas system and its application in tomato breeding

“…Transcription factor SlMYC2 is the master regulator of methyl jasmonate signaling pathway (Kazan and Manners 2013 ). Knockout of SlMYC2 significantly reduced the expression level of both disease defensive genes and genes related to jasmonic acid pathway, suggesting its prominent role in methyl jasmonate-induced disease resistance in tomato (Shu et al 2020 ).…”

Defense Strategies: The Role of Transcription Factors in Tomato–Pathogen Interaction

“…The bHLH MYC2 TF was identified as master regulator in the JA signaling pathway [ 103 ]. In fact, it was already verified that the knockout of the tomato SlMYC2 caused a significant decrease of the expression of the PR genes SlPR-1 and SlPR-STH2 and of genes linked to the signaling pathway and JA biosynthesis, besides a decrease on the activities of disease defensive and antioxidant enzymes, with a consequent exacerbation of the B. cinerea disease symptoms [ 94 ].…”

“…MYC2 -Knockout aggravated the B. cinerea disease symptoms. CRISPR/Cas9 [94] bZIP SlAREB1 -Overexpression up-regulate several defense genes associated with biotic stress.…”

Overexpressing the N‐terminus of CATALASE2 enhances plant jasmonic acid biosynthesis and resistance to necrotrophic pathogen Botrytis cinerea B05.10

“…Botrytis cinerea is a typical fungal pathogen with a necrotrophic lifestyle attacking over 200 crop hosts worldwide, which kills plant cells and consumes the nutrient contents (Shu et al, 2020 ; Williamson et al, 2007 ; Xiong et al, 2019 ). When infected by B .…”

“…Botrytis cinerea is a typical fungal pathogen with a necrotrophic lifestyle attacking over 200 crop hosts worldwide, which kills plant cells and consumes the nutrient contents (Shu et al, 2020;Williamson et al, 2007;Xiong et al, 2019). When infected by B. cinerea, plants activate both jasmonic acid (JA) biosynthesis and JA signalling to enhance their immune responses (Liao et al, 2020;Xiong et al, 2019).…”