Functional Characterization of9-/13-LOXsin Rice and Silencing Their Expressions to Improve Grain Qualities

Abstract

Lipoxygenases (LOXs) are involved in oxidative rancidity and render rice unsuitable for human consumption. Here, RNA interference- (RNAi-) induced gene expression inhibition was used to analyze the functions of the bran/seed-specific LOXs in rice.r9-LOX1andL-2(9-LOX category) were the candidate genes expressing a bran/seed-specific LOX, whileRCI-1was (13-LOX category) a plastid-specific LOX. Real-time PCR showed that three LOXs were cultivar/tissue specific expression on a certain level.r9-LOX1andL-2were generally much higher in active bran/seed than in stabilized bran, mature seed, and regenerated plant.RCI-1was barely expressed in seed. In transgenic lines,r9-LOX1, as well asL-2, expression was dramatically downregulated, compared to the nontransgenic controls. SPME/GC-MS analysis ofr9-LOX1RNAi transgenic lines showed 74.33% decrease in nonanal content (formed during oxidation of linoleic acid by lipoxygenase), but 388.24% increase in acetic acid and 184.84% hexanal (direct products of 13-LOX). These results indicate thatr9-LOX1positively regulates the amount of nonanal but negatively regulates acetic acid and hexanal. The negative regulation may be due to a mechanism of negative feedback between LOX family members. The information will help comprehensively understand the function of the bran/seed-specific LOXs,r9-LOX1, and improve the storage quality in the future.