Department of Postharvest Science of Fresh Produce, Institute of Technology and Storage of Agricultural Products, the Volcani Center, Agricultural Research Organization, PO Box 6, Bet Dagan 50250, Israel.
Mol Plant Pathol. 2004 Nov 1;5(6):575-85. doi: 10.1111/j.1364-3703.2004.00249.x.
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.
在鳄梨中，具有最强抗真菌活性的物质是前体（Z,Z）-1-乙酰氧基-2-羟基-4-氧代-heneicosa-12,15-二烯（AFD），它可使未成熟果实中的炭疽病菌进入休眠状态。推测编码Δ（12）脂肪酸去饱和酶（avfad12）的一个基因参与 AFD 的生物合成，并根据 AFD 的含量确定其表达模式和酶活性。使用 avfad12-3 作为探针，在含有最高 AFD 水平的幼果和叶片中检测到高水平的表达。相反，对来自成熟叶片和果实的 RNA 的 Northern 分析显示，avfad12 基因家族没有转录物，AFD 含量也较低。当果实被炭疽病菌接种或暴露于乙烯（40 μL/L）、低温（4°C）或 1 mM H2O2 时，未成熟抗性果实中的 avfad12 基因家族的转录物、Δ（12）脂肪酸去饱和酶的活性和 AFD 的水平会短暂增加，但成熟果实不受影响。H2O2 对 avfad12 基因家族转录物的影响特别重要，因为未成熟抗性宿主果实在接种炭疽病菌后不久就会产生活性氧。此外，真菌本身在 pH 5.0 的培养基中产生 H2O2，与未成熟抗性果实的 pH 相似，但在 pH 7.0 时不产生。增强 Δ（12）脂肪酸去饱和酶活性的处理增加了 AFD 前体亚油酸的浓度及其向 AFD 的转化；这些处理还导致腐烂发展的延迟。目前的结果表明，avfad12 基因家族的转录物、AFD 前体（亚油酸）的合成、AFD 含量以及未成熟果实中炭疽病菌的休眠之间存在时间关系。
