WRKY33‐mediated indolic glucosinolate metabolic pathway confers resistance against Alternaria brassicicola in Arabidopsis and Brassica crops

Abstract

The tryptophan (Trp)‐derived plant secondary metabolites, including camalexin, 4‐hydroxy‐indole‐3‐carbonylnitrile, and indolic glucosinolate (IGS), show broad‐spectrum antifungal activity. However, the distinct regulations of these metabolic pathways among different plant species in response to fungus infection are rarely studied. In this study, our results revealed that WRKY33 directly regulates IGS biosynthesis, notably the production of 4‐methoxyindole‐3‐ylmethyl glucosinolate (4MI3G), conferring resistance to Alternaria brassicicola, an important pathogen which causes black spot in Brassica crops. WRKY33 directly activates the expression of CYP81F2, IGMT1, and IGMT2 to drive side‐chain modification of indole‐3‐ylmethyl glucosinolate (I3G) to 4MI3G, in both Arabidopsis and Chinese kale (Brassica oleracea var. alboglabra Bailey). However, Chinese kale showed a more severe symptom than Arabidopsis when infected by Alternaria brassicicola. Comparative analyses of the origin and evolution of Trp metabolism indicate that the loss of camalexin biosynthesis in Brassica crops during evolution might attenuate the resistance of crops to Alternaria brassicicola. As a result, the IGS metabolic pathway mediated by WRKY33 becomes essential for Chinese kale to deter Alternaria brassicicola. Our results highlight the differential regulation of Trp‐derived camalexin and IGS biosynthetic pathways in plant immunity between Arabidopsis and Brassica crops.

A high-efficiency PEG-Ca2+-mediated transient transformation system for broccoli protoplasts

“…And the Bol029100 and Bol031350 genes encode FMO GS- OX5 (flavin-containing monooxygenase, FMO GS-OX5 ); broccoli contains two homologous copies of this gene ( Wang et al., 2011 ; Zhao et al., 2021 ), which is present in only one copy in Arabidopsis ( AT1G12140 ) ( Kong et al., 2016 ). The gene encodes flavin monooxygenase (FMO GS-OX ), which catalyzes the oxidation of sulfur atoms in methylthioalkyl mustard oleosides (MT GSLs) to produce the anticancer active precursor of sulforaphane (SFN, SF), 4-methyl sulfinyl butylthioside (glucoraphanin, GRA) ( Lee et al., 2017 ; Wang et al., 2017 ; Tao et al., 2022 ). While we found that two homologous copies of the gene are present in broccoli, and the functional differences between these genes need to be further verified.…”

Genome-Wide Association Study of Glucosinolate Metabolites (mGWAS) in Brassica napus L.

“…In the current study, we identified 39 transcription factors that were predicted to regulate GSL biosynthesis, including 15 AP2/ERF transcription factors (ERFs, ARF3, DREBs and ANT), seven zinc finger proteins (CZF1, STZ, ZHDs, DOF1, OBP2 and ZFP4), two WRKY transcription factors (WRKY33), one growth regulator (GRF1), one NAC family protein (NAC102), one E2F transcription factor (E2FC), one nuclear transcription factor Y subunit B (NF-YB10) and 11 MYB transcription factors (MYBs). Among these, homologous genes of MYB34 , MYB51 , MYB122 and WRKY33 , which are involved in GSL biosynthesis [ 42 , 70 ], were identified on the interval regions of chromosomes A03, A04, A07, A09, C02, C06, C08 and C09, respectively ( Table S4 ). We also identified some novel transcription factor genes (e.g., MYB44, ERF025, NF-YB10 and E2FC) associated with the significant SNPs, with obvious differences in expression in developing seeds of BnHG and BnLG ( Figure 5 , Table S4 ).…”

“…Furthermore, MYC2, MYC3 and MYC4 interact with multiple MYB transcription factors (e.g., MYB28, MYB29, MYB34, MYB51 and MYB76), thereby contributing to GSL biosynthesis [ 40 , 41 ]. A recent study showed that WRKY33 not only directly targets the promoters of the gene MYB51 and the GSL biosynthesis gene CYP83B1 to regulate the de novo biosynthesis of indole GSLs, but also regulates the expression of genes involved in side chain modification ( CYP81F2 , IGMT1 and IGMT2 ), thereby increasing the biosynthesis of indole GSLs [ 42 ].…”

BcWRKY33A Enhances Resistance to Botrytis cinerea via Activating BcMYB51-3 in Non-Heading Chinese Cabbage

“…Among them, R2R3-MYB types are superior in numbers in plants, including our BcMYB51s. The importance of MYB TFs in the various programs of plants was shown in previous data, including but not limited to cell morphogenesis and differentiation [ 45 , 46 ], trichome development [ 47 ], hormone responses [ 48 ], abiotic and biotic stress [ 49 , 50 ], and light response [ 51 ]. Regarding MYB51 and its homologs, AtMYB51 was up-regulated after wound treatment [ 52 ].…”

“…Under B. cinerea infection, BcWRKY33A showed an earlier and sharper increase than BcMYB51-3 at 12 h ( Figure 5 a), so it is reasonable and understandable that BcMYB51-3 functions downstream of BcWRKY33A in NHCC plants. Coincidentally, a recent study revealed that WRKY33 could activate the expression of IGS-related genes, then enhance the Arabidopsis and Brassica crop resistance against another necrotrophic fungus, Alternaria brassicicola [ 50 ]. Thus, the importance of MYB51, the homolog of BcMYB51-3, in BcWRKY33A-mediated resistance to B. cinerea was checked ( Figure 7 ).…”