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Functional Characterization of 9-/13-LOXs in Rice and Silencing Their Expressions to Improve Grain Qualities

M. RoyChowdhury,Xiaobai Li,Hangying Qi,Wenxu Li,Jian Sun,Cheng Huang,Dianxing Wu

Published 2016 in BioMed Research International

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-LOX1 and L-2 (9-LOX category) were the candidate genes expressing a bran/seed-specific LOX, while RCI-1 was (13-LOX category) a plastid-specific LOX. Real-time PCR showed that three LOXs were cultivar/tissue specific expression on a certain level. r9-LOX1 and L-2 were generally much higher in active bran/seed than in stabilized bran, mature seed, and regenerated plant. RCI-1 was barely expressed in seed. In transgenic lines, r9-LOX1, as well as L-2, expression was dramatically downregulated, compared to the nontransgenic controls. SPME/GC-MS analysis of r9-LOX1 RNAi 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 that r9-LOX1 positively 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.

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