An oriental melon 9-lipoxygenase gene CmLOX09 response to stresses, hormones, and signal substances

Abstract

In plants, lipoxygenases (LOXs) play a crucial role in biotic and abiotic stresses. In our previous study, five 13-LOX genes of oriental melon were regulated by abiotic stress but it is unclear whether the 9-LOX is involved in biotic and abiotic stresses. The promoter analysis revealed that CmLOX09 (type of 9-LOX) has hormone elements, signal substances, and stress elements. We analyzed the expression of CmLOX09 and its downstream genes-CmHPL and CmAOS-in the leaves of four-leaf stage seedlings of the oriental melon cultivar "Yumeiren" under wound, hormone, and signal substances. CmLOX09, CmHPL, and CmAOS were all induced by wounding. CmLOX09 was induced by auxin (indole acetic acid, IAA) and gibberellins (GA₃); however, CmHPL and CmAOS showed differential responses to IAA and GA₃. CmLOX09, CmHPL, and CmAOS were all induced by hydrogen peroxide (H₂O₂) and methyl jasmonate (MeJA), while being inhibited by abscisic acid (ABA) and salicylic acid (SA). CmLOX09, CmHPL, and CmAOS were all induced by the powdery mildew pathogen Podosphaera xanthii. The content of 2-hexynol and 2-hexenal in leaves after MeJA treatment was significantly higher than that in the control. After infection with P. xanthii, the diseased leaves of the oriental melon were divided into four levels-levels 1, 2, 3, and 4. The content of jasmonic acid (JA) in the leaves of levels 1 and 3 was significantly higher than that in the level 0 leaves. In summary, the results suggested that CmLOX09 might play a positive role in the response to MeJA through the hydroperoxide lyase (HPL) pathway to produce C6 alcohols and aldehydes, and in the response to P. xanthii through the allene oxide synthase (AOS) pathway to form JA.

Keywords: 9-Lipoxygenase (9-LOX); Hydroperoxide lyase (HPL); Allene oxide synthase (AOS); Green leaf volatile; Jasmonic acid.

Fig. 1

Expression patterns of CmLOX09, CmHPL, and CmAOS after wounding treatment (a) Expression pattern of CmLOX09 after wounding treatment. (b) Expression pattern of CmHPL after wounding treatment. (c) Expression pattern of CmAOS after wounding treatment. Data are presented as mean±standard error from three replicates with three biological repeats. ^* P<0.05, ^** P<0.01, compared to the respective control (CK) at each point

Fig. 2

Expression patterns of CmLOX09, CmHPL, and CmAOS after IAA (100 μmol/L) and GA₃ (100 μmol/L) treatments (a) Expression patterns of CmLOX09 after IAA treatment. (b) Expression patterns of CmHPL after IAA treatment. (c) Expression patterns of CmAOS after IAA treatment. (d) Expression patterns of CmLOX09 after GA₃ treatment. (e) Expression patterns of CmHPL after GA₃ treatment. (f) Expression patterns of CmAOS after GA₃ treatment. Data are presented as mean±standard error from three replicates with three biological repeats. ^* P<0.05, ^** P<0.01, compared to the respective control at each point

Fig. 3

Expression patterns of CmLOX09, CmHPL, and CmAOS after ABA (100 μmol/L), SA (5 mmol/L), H₂O₂(10 mmol/L), and MeJA (100 μmol/L) treatments (a) Expression patterns of CmLOX09 after ABA treatment. (b) Expression patterns of CmHPL after ABA treatment. (c) Expression patterns of CmAOS after ABA treatment. (d) Expression patterns of CmLOX09 after SA treatment. (e) Expression patterns of CmHPL after SA treatment. (f) Expression patterns of CmAOS after SA treatment. (g) Expression patterns of CmLOX09 after H₂O₂ treatment. (h) Expression patterns of CmHPL after H₂O₂ treatment. (i) Expression patterns of CmAOS after H₂O₂ treatment. (j) Expression patterns of CmLOX09 after MeJA treatment. (k) Expression patterns of CmHPL after MeJA treatment. (l) Expression patterns of CmAOS after MeJA treatment. Data are presented as mean±standard error from three replicates with three biological repeats. ^* P<0.05, ^** P<0.01, compared to the respective control at each point

Fig. 4

Levels of 2-hexynol and 2-hexenal in oriental melon treatment and control leaves after MeJA treatment (a) 2-Hexynol release from oriental melon leaves after treatment at 6, 72, and 168 h. (b) 2-Hexenal release from oriental melon leaves after treatment at 6, 72, and 168 h. Data are presented as mean±standard error from three replicates with three biological repeats. ^** P<0.01, compared to the respective control at each point

Fig. 5

Expression patterns of CmLOX09, CmHPL, and CmAOS after inoculation with Podosphaera xanthii treatments (a) Different disease grades in oriental melon leaves after inoculated with P. xanthii. (b) Expression patterns of CmLOX09 after inoculated with P. xanthii. (c) Expression patterns of CmHPL after inoculated with P. xanthii. (d) Expression patterns of CmAOS after inoculated with P. xanthii. Numbers indicate the different disease grades (0, no lesions; 1, a mild disease, lesion area 0%–25%; 2, the onset of mild, lesion area 25%–50%; 3, moderate incidence, lesion area 50%–75%; 4, severe disease, lesion area >75%). Data are presented as mean±standard error from three replicates with three biological repeats. ^** P<0.01 compared to the healthy leaves (0)

Fig. 6

Level of JA in oriental melon leaves after inoculation with Podosphaera xanthii Data are presented as mean±standard error from three replicates with three biological repeats. ^* P<0.05, ^** P<0.01, compared to the healthy leaves (0)