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"(a) Comparison of the gross morphology of wild-type andoni1-1(inset) at the same magnification. (b) Enlarged gross morphology of oni1-1. (c) Transgenic shoot over-expressing OSH1.(from referenc[1])."

ONI1 gene is originally derived from Oryza sativa Japonica Group(cultivar: Nipponbare). It encodes an fatty acid elongase involved in the synthesis of very-long-chain fatty acids, which are the component of extracellular waxes[2].

It's the key gene for correct acid composition and normal shoot development in rice. Mutation of ONI1 will induce a reduced amount of very-long-chain fatty acids[1] and failure of the maintenance of SAM and ectopic expression of SAM-specific KNOX genes in leaf. ONI1 was specifically expressed in the outermost cell layer of the shoot apical meristem and developing lateral organs. These results show that fatty acid elongase is required for formation of the outermost cell layer, and this layer is indispensable for entire shoot development in rice[3].

Although oni1 showed organ fusions as is the case in Arabidopsisfdh, the oni1 mutants lacked a normal outermost cell layer (layer 1 or L1) and failed to maintain the shoot apical meristem (SAM). Along with the expression of ONI1in embryogenesis, defects in the SAM were also observed even at this stage. In addition,oni1had a reduced amount of VLCFAs. Consistent with these phenotypic differences, FDH failed to complement the oni1 mutation. These results suggest that rice fatty acid elongase ONI1 has a more critical function than Arabidopsis FDH in plant development, or ONI1 has an additional function to that of FDH[1].


"(b–k) In situ RNA hybridization ofONI1. Longitudinal sections were hybridized with the antisense probe (b–j) or control sense probe (k) forONI1. Embryos at (b) 3, (c) 4, (d) 5, (e) 7 and (f) 10 days after pollination. (g) Shoot apex of a 1-day imbibed seed. (h) Shoot apex of a 1-month-old plant. (i) Developing panicle. (j) Developing flower. (k) Shoot apex of a 1-day imbibed seed hybridized with the sense probe (from referenc[1])."

This gene expresse in the outermost cells of the embryo, SAM, young leaves and floral organs.

At 3 days after pollination, ONI1 expression can be detected in the outermost cells of a globular embryo.

At 4-5 days after pollination, ONI1 expression can be detected in L1 of newly developed shoot organ as well as outermost cells of the embryo.

At 7-10 days after pollination, ONI1 expression can also be detected in L1, but the quantity is reduced.

During vegetative growth phase (within one month after germination), ONI1 expression can be detected in L1 of SAM and young leaves.

During reproductive growth phase, ONI1 expression can be detected in L1 of the developing panicle and floral organs.

In conclusion, ONI1 is an L1-specific gene of the SAM and young above-ground organs[2].


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Labs working on this gene

Plant Genetics Laboratory, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka-ken, 411-8540 Japan

Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai, 981-8555 Japan

State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, 100101 Beijing, People’s Republic of China

Institute of Cellular and Molecular Botany, Department of Ecophysiology, University of Bonn, 53115 Bonn, Germany


  1. 1.0 1.1 1.2 1.3 Tsuda K, Akiba T, Kimura F, Ishibashi M, Moriya C, Nakagawa K, Kurata N, Ito Y. ONION2 fatty acid elongase is required for shoot development in rice. Plant Cell Physiol. 2013;54(2):209-17.
  2. 2.0 2.1 Ito Y, Kimura F, Hirakata K, Tsuda K, Takasugi T, Eiguchi M, Nakagawa K, Kurata N. Fatty acid elongase is required for shoot development in rice. Plant J. 2011;66(4):680-688.
  3. Takasugi T, Ito Y. Altered expression of auxin-related genes in the fatty acid elongase mutant oni1 of rice. Plant Signal Behav. 2011;6(6):887-888.

Structured Information