Expression of Δ¹² fatty acid desaturase during the induced accumulation of the antifungal diene in avocado fruits

Abstract

SUMMARY The preformed (Z,Z)-1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene (AFD) is the most active antifungal compound in avocado; it affects the quiescence of Colletotrichum gloeosporioides in unripe fruit. One of the genes encoding Delta(12) fatty acid desaturase (avfad12) was hypothesized to take part in the biosynthesis of AFD, and its expression pattern and enzymatic activity were determined in relation to the content of AFD. Using avfad12-3 as a probe, high levels of expression were detected in young fruits and leaves, where the level of AFD was highest. In contrast, Northern analysis of RNA from mature leaves and fruits showed no transcripts from the avfad12 gene family and lower AFD content. The transcripts from the avfad12 gene family, the enzymatic activity of Delta(12) fatty acid desaturase, and the level of AFD in unripe-resistant fruits increased transiently when the fruits were inoculated with C. gloeosporioides or exposed to ethylene (40 microL/L), low temperature (4 degrees C) or 1 mm H(2)O(2), but ripe fruits were not affected. The effect of H(2)O(2) on the transcripts from the avfad12 gene family is of specific importance, because reactive oxygen species were produced by unripe-resistant host fruit soon after inoculation of C. gloeosporioides. In addition, the fungus itself produced H(2)O(2) in culture medium at pH 5.0, which is similar to the pH of unripe-resistant fruit, but not at pH 7.0. Treatments that enhanced Delta(12) fatty acid desaturase activity increased the concentration of the AFD precursor, linoleic acid, and its incorporation into AFD; these treatments also caused a delay in decay development. The present results demonstrate temporal relationships among the transcripts from the avfad12 gene family, the synthesis of the precursor of AFD (linoleic acid), the AFD content and quiescence of C. gloeosporioides in unripe fruits.

Virus-Induced Alterations in Primary Metabolism Modulate Susceptibility toTobacco rattle virusin Arabidopsis

“…On the other hand, the observed increase of linoleic acid and the decrease of linolenic acid detected in chloroplast lipids such as MGDG, DGDG, SQ, and PG are consistent with the detected induction of the extraplastidial oleate desaturase FAD2 and the repression of the plastidial desaturases FAD5, FAD6, and FAD8 in infected leaves. The involvement of the FAD2 gene in the response to biotic stresses has been described in parsley (Petroselinum crispum) cell cultures supplemented with a fungal elicitor (Kirsch et al, 1997) and in fungus-infected avocado (Persea americana) fruits (Wang et al, 2004). In these cases, it has been suggested that the accumulation of polyunsaturated fatty acids could compensate for losses caused by the elimination of lipid hydroperoxides from membrane injury during the oxidative burst and/or by the conversion of polyunsaturated fatty acids to signal molecules such as jasmonates (Kirsch et al, 1997).…”

“…Table I. Effect of TRV infection on the content and fatty acid composition of lipid classes in Arabidopsis leaves at 8 dpi low-salt and low-temperature tolerance in Arabidopsis, the involvement of the FAD2 gene in response to biotic stress has been widely documented (Miquel et al, 1993;Kirsch et al, 1997;Wang et al, 2004;Zhang et al, 2012). In this scenario, accumulation of polyunsaturated fatty acids could compensate for losses caused by the elimination of lipid hydroperoxides during the oxidative burst (Kirsch et al, 1997).…”

Mechanisms modulating fungal attack in post-harvest pathogen interactions and their control

“…The pH is also changed, or induced to change, by the pathogens around the infection site (Beno-Moualem and Prusky 2000; Wang et al 2004). Thus, an increase in the natural pH during fruit ripening or as a result of fungal activity can suppress oxidative responses of either the pathogen or the host, and so facilitate activation of the quiescent infection.…”

Identification and Functional Analysis of a Δ6-Desaturase Gene and the Effects of Temperature and Wounding Stresses on Its Expression inMicroula sikkimensisLeaves

“…13) Plant fatty acid desaturases are regulated by various environmental factors. 1) Much research suggests that temperature can regulate fatty acid desaturases at the transcriptional and post-transcriptional levels, as described for FAD2 in several plants, 3,5,33) for FAD6 in olive fruit, 34) for FAD3 in wheat roots, 2) and for FAD8 in Arabidopsis leaves, 35) but no effect of temperature on the expression of the Á6-desaturase gene has been demonstrated in higher plants. In the present study, when plants were incubated at low temperature, an increase in MsD6DES expression levels was observed (Fig.…”