In rice (Oryza sativa) roots, lysigenous aerenchyma, which is created by programmed cell death and lysis of cortical cells, is constitutively formed under aerobic conditions, and its formation is further induced under oxygen-deficient conditions. Ethylene is involved in the induction of aerenchyma formation. reduced culm number1 (rcn1) is a rice mutant in which the gene encoding the ATP-binding cassette transporter RCN1/OsABCG5 is defective. Here, we report that the induction of aerenchyma formation was reduced in roots of rcn1 grown in stagnant deoxygenated nutrient solution (i.e. under stagnant conditions, which mimic oxygen-deficient conditions in waterlogged soils). 1-Aminocyclopropane-1-carboxylic acid synthase (ACS) is a key enzyme in ethylene biosynthesis. Stagnant conditions hardly induced the expression of ACS1 in rcn1 roots, resulting in low ethylene production in the roots. Accumulation of saturated very-long-chain fatty acids (VLCFAs) of 24, 26, and 28 carbons was reduced in rcn1 roots. Exogenously supplied VLCFA (26 carbons) increased the expression level of ACS1 and induced aerenchyma formation in rcn1 roots. Moreover, in rice lines in which the gene encoding a fatty acid elongase, CUT1-LIKE (CUT1L; a homolog of the gene encoding Arabidopsis CUT1, which is required for cuticular wax production), was silenced, both ACS1 expression and aerenchyma formation were reduced. Interestingly, the expression of ACS1, CUT1L, and RCN1/OsABCG5 was induced predominantly in the outer part of roots under stagnant conditions. These results suggest that, in rice under oxygen-deficient conditions, VLCFAs increase ethylene production by promoting 1-aminocyclopropane-1-carboxylic acid biosynthesis in the outer part of roots, which, in turn, induces aerenchyma formation in the root cortex.
水稻根部的溶生性通氣組織是由細(xì)胞程序性死亡和皮層細(xì)胞溶解形成的，在需氧條件下組成性形成，缺氧條件會進(jìn)一步誘導(dǎo)它的形成。乙烯參與誘導(dǎo)通氣組織的形成，rcn1是一個水稻突變體，它的ATP結(jié)合盒轉(zhuǎn)運蛋白RCN1/OsABCG5編碼基因缺陷。本文，我們報道了rcn1在停滯脫氧條件下（如在停滯條件下，可以模擬淹水土壤的缺氧條件）生長時，根部通氣組織形成的誘導(dǎo)作用減弱。氨基環(huán)丙烷羧合酶（ACS）是乙烯合成中的一個關(guān)鍵酶。停滯條件幾乎不會誘導(dǎo)rcn1根部ACS1的表達(dá)，導(dǎo)致根部產(chǎn)生的乙烯較少。rcn1根部的24、26、28碳飽和極長鏈脂肪酸（VLCFAs）的積累減少。外源施加VLCFA（26碳）會增加rcn1根部ACS1的表達(dá)水平，并誘導(dǎo)通氣組織的形成。此外，脂肪酸延長酶CET1-LIKE（CUT1L，是擬南芥CUT1編碼基因的同源基因，CUT1參與角質(zhì)層蠟質(zhì)的產(chǎn)生）編碼基因被沉默的水稻株系中，ACS1的表達(dá)和通氣組織的形成均降低。有意思的是，在停滯條件下，根外部ACS1、CUT1L和RCN1/OsABCG5的表達(dá)受到顯著誘導(dǎo)。這些結(jié)果表明，水稻在缺氧條件下生長時，VLCFAs通過促進(jìn)根外部氨基環(huán)丙烷羧合酶的合成，增加乙烯的產(chǎn)生，進(jìn)而誘導(dǎo)根系皮層中通氣組織的形成。