Oxylipin KODA enhances the early growth of rice (Oryza sativa L.) under low-temperature stress at night to simulate a natural temperature condition.

α-Ketol octadecadienoic acid (KODA), an oxylipin, has stimulatory effects on flowering, rooting, and resistance to pathogens. It also increases the yield of rice, Oryza sativa L. Here we examined the effects of KODA on the early growth of rice under various temperature conditions. KODA was applied by imbibing seeds in 1 µM KODA solution overnight. KODA treatment did not promote the growth at 25°C or 28°C, which are appropriate temperatures for rice cultivation. At a constant temperature of 15°C, seedling growth was poor, and KODA application did not promote seedling growth. On the other hand, at a night temperature of 15°C and day temperature of 25°C, KODA prominently enhanced the growth. We analyzed the transcript levels of several marker genes associated with chilling signaling and stress tolerance in rice. The expression of the dehydration-responsive-element-binding protein 1/C-repeat binding factor (DREB1/CBF), which regulate the expression of many stress-responsive genes was promoted. The expression of the late embryogenesis abundant (LEA), which has a DRE/CRT cis-element, was also increased by KODA treatment. Additionally, the expression of the b-amylase 4 (OsBMY4), which is important for starch degradation during cold-stress adaptation in rice, and that of the probenazole-induced protein 1 (PBZ1), a molecular marker in the rice immune response, were significantly elevated in KODA-treated rice. Thus, the enhanced growth of KODA-treated rice under chilling stress may be attributed, at least in part, to the enhanced transcriptional regulatory network mediated by DREB1/CBF genes and sugar metabolism, including starch degradation mediated by abscisic acid.