Cloning, characterization and expression analysis of a 9-lipoxygenase gene in Gladiolus hybridus

Plant lipoxygenases (LOXs) is a functionally diverse class of dioxygenases involved in multiple physiological processes such as growth, senescence, and stress-related responses. Previously, based on the analysis of LOX1 activity and corm formation, it was depicted that LOX1 increased jasmonic acid (JA) synthesis and induced enlargement at top of stolon branches, forming cormels in Gladiolus hybridus. Here, LOX gene (GhLOX1) in full length was isolated from developing corms in G. hybridus. Sequence analysis showed that GhLOX1 was a novel LOX1 gene encoding 9-LOX. Transient expression analysis determined GhLOX1 to be a cytoplasm protein. Real time RT-PCR showed that the mRNA level of GhLOX1 gene correlated positively with LOX activity and was highest in cormels. GhLOX1 mRNA level, LOX activity and endogenous methyl jasmonate (MJ) content in corms increased steadily with a MJ gradient from 0.1 mmol/L to 0.5 mmol/L. Conversely, GhLOX1 mRNA level, LOX activity, and endogenous MJ content in corms steadily decreased with the increasing concentration of Salicylhydroxamic acid (SHAM). At the same time, we observed that MJ and SHAM treatments effected both LOX1 mRNA level and LOX activity, leading to promotion and inhibition of corm formation and enlargement, respectively. These data reveal that GhLOX1 is a novel LOX1 gene encoding a cytoplasm 9-LOX protein and its expression would contribute to LOX activity which plays an important role in corm formation and enlargement. In general, GhLOX1 is an ideal candidate for the promotion of corm formation and enlargement by gene manipulation in G. hybridus.

► We isolate a novel LOX1 gene encoding 9-LOX from developing corms in Gladiolus hybridus.
► We analyze the GhLOX1 gene expression patterns in different organs of Gladiolus hybridus.
► Exogenous MJ increases the GhLOX1 expression level and promotes the corm enlargement.
► As an inhibitor of LOX, SHAM decreases the GhLOX1 expression level and inhibits the corm enlargement.