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.

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Glucosinolates, anthocyanins, total phenols, and vitamin C, as well as antioxidant capacity, were investigated in Chinese kale sprouts treated with both glucose and gibberellic acid (GA 3 ). The combination of 3% (0.03 g/ml) glucose and 5 μmol/L GA 3 treatment was effective in increasing glucosinolate content while glucose or GA 3 treatment alone did not influence significantly almost all individual glucosinolates or total glucosinolates. The total phenolic content and antioxidant activity of Chinese kale sprouts were enhanced by combined treatment with glucose and GA 3 , which could be useful in improving the main health-promoting compounds and antioxidant activity in Chinese kale sprouts.

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