Abstract
Allene oxide synthase (AOS) and hydroperoxide lyase (HPL), members of the CYP74 gene family, are branches of the oxylipin pathway and play vital roles in plant responses to a number of stresses. In this study, four HPL genes and one AOS gene were identified in the watermelon genome, which were clustered into three subfamilies (CYP74A, CYP74B and CYP74C). Sequence analysis revealed that most HPL and AOS proteins from various plants contain representative domains, including Helix-I region, Helix-K region (ExxR) and Heme-binding domain. A number of development-, stress-, and hormone-related cis-elements were found in the promoter regions of the ClAOS and ClHPL genes, and the detected ClAOS and ClHPL genes were differentially expressed in different tissues and fruit development stages, as well as in response to various hormones. In addition, red light could enhance the expression of ClAOS in root-knot nematode-infected leaves and roots of watermelon, implying that ClAOS might play a primary role in red light-induced resistance against root-knot nematodes. These findings lay a foundation for understanding the specific function of CYP74 genes in watermelon.
Highlights
Oxylipins are oxygenated derivatives from the oxidation of polyunsaturated fatty acids (PUFAs), which include jasmonic acid (JA) and its related compounds, as well as other molecules such as hydroxy, oxo- or keto-fatty acids [1,2,3]
Four hydroperoxide lyase (HPL) genes and one Allene oxide synthase (AOS) gene were identified in the watermelon genome and were designated as ClHPL1–ClHPL4 and ClAOS based on their chromosome locations (Table 1)
The five watermelon CYP74 genes were irregularly distributed on two chromosomes of the watermelon genome
Summary
Oxylipins are oxygenated derivatives from the oxidation of polyunsaturated fatty acids (PUFAs), which include jasmonic acid (JA) and its related compounds, as well as other molecules such as hydroxy-, oxo- or keto-fatty acids [1,2,3]. The fatty acid hydroperoxides undergo several secondary conversions controlled by CYP74, which belongs to the superfamily of cytochrome P450 enzymes [4]. Allene oxide synthase (AOS), hydroperoxide lyase (HPL), and divinyl ether synthase (DES) are members of the CYP74 family, which can catalyze the Agronomy 2019, 9, 872; doi:10.3390/agronomy9120872 www.mdpi.com/journal/agronomy. Agronomy 2019, 9, 872 isomerization or dehydration of fatty acid hydroperoxides and require neither molecular oxygen nor NAD(P)H-dependent cytochrome P450-reductase [1,2,6]. CYP74 enzymes are broadly classified into four subfamilies (CYP74A, CYP74B, CYP74C, and CYP74D) based on their evolutionary heritage and relationship with the diversity of oxylipin structure [6]. AOS and DES members constitute the CYP74A and CYP74D subfamily, respectively, while CYP74B and CYP74C subfamilies contain enzymes with HPL activity [5,7]. AOS enzymes can be classified into three different types: The first two types can use either
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