Enhanced expression of avfae1 encoding a long-chain fatty acid elongase during the induction of the antifungal diene in avocado fruits

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 nature of infection of unripe fruit by  Colletotrichum  gloeosporioides. Fatty acid elongase was hypothesized to participate in the  biosynthesis  of AFD, therefore the  enzymatic activity  of avocado fatty acid elongase (AVFAE) and the expression pattern of one of the genes encoding this enzyme were determined. Using  avfae1  as a probe, high expression was detected in young fruits and leaves, those being the organs in which the incorporation of the AFD precursor,  linoleic acid , and the level of AFD were the highest. In contrast, no expression of  avfae1  could be detected in mature leaves and fruits and the content of AFD was lower. The expression of  avfae1 , the enzymatic activity of fatty acid elongase, and the level of AFD in unripe-resistant fruits increased transiently when the fruits were exposed to ethylene (40 μl/l), low temperature (4 °C) or 1 mM H 2 O 2 , but ripe fruits were not affected. The present results suggest that the elongation of the linoleic acid is an important step in the biosynthesis of AFD, and hence, in the quiescence of  C. gloeosporioides  in unripe fruits.