Ethylene Promotes Submergence-Induced Expression of OsABA8ox1, a Gene that Encodes ABA 8'-Hydroxylase in Rice

Abstract

A rapid decrease of the plant hormone ABA under submergence is thought to be a prerequisite for the enhanced elongation of submerged shoots of rice (Oryza sativa L.). Here, we report that the level of phaseic acid (PA), an oxidized form of ABA, increased with decreasing ABA level during submergence. The oxidation of ABA to PA is catalyzed by ABA 8'-hydroxylase, which is possibly encoded by three genes (OsABA8ox1, -2 and -3) in rice. The ABA 8'-hydroxylase activity was confirmed in microsomes from yeast expressing OsABA8ox1. OsABA8ox1-green fluorescent protein (GFP) fusion protein in onion cells was localized to the endoplasmic reticulum. The mRNA level of OsABA8ox1, but not the mRNA levels of other OsABA8ox genes, increased dramatically within 1 h after submergence. On the other hand, the mRNA levels of genes involved in ABA biosynthesis (OsZEP and OsNCEDs) decreased after 1-2 h of submergence. Treatment of aerobic seedlings with ethylene and its precursor, 1-aminocyclopropane-1-carboxylate (ACC), rapidly induced the expression of OsABA8ox1, but the ethylene treatment did not strongly affect the expression of ABA biosynthetic genes. Moreover, pre-treatment with 1-methylcyclopropene (1-MCP), a potent inhibitor of ethylene action, partially suppressed induction of OsABA8ox1 expression under submergence. The ABA level was found to be negatively correlated with OsABA8ox1 expression under ACC or 1-MCP treatment. Together, these results indicate that the rapid decrease in ABA levels in submerged rice shoots is controlled partly by ethylene-induced expression of OsABA8ox1 and partly by ethylene-independent suppression of genes involved in the biosynthesis of ABA.

A Co-Opted Hormonal Cascade Activates Dormant Adventitious Root Primordia upon Flooding in Solanum dulcamara

“…3C). A similar negative relation between ethylene and ABA accumulation has been described earlier in shoot growth responses to flooding in R. palustris and rice (Saika et al, 2007;van Veen et al, 2013) and in germinating seeds and seedlings in Order of lines is according to significance of difference with the wild type. Data are means 6 SE (n = 2-4).…”

SOMNUS, a CCCH-Type Zinc Finger Protein inArabidopsis, Negatively Regulates Light-Dependent Seed Germination Downstream of PIL5

“…2 H-labeled GAs (purchased from Lewis Mander, Australian National University) were used as internal standards. Endogenous ABA levels were determined by liquid chromatography-tandem mass spectrometry using ½ 2 H 6 ABA (Icon Services) as an internal standard, as reported previously (Saika et al, 2007).…”

Waterproofing Crops: Effective Flooding Survival Strategies

“…3). Ethylene entrapped during submergence stimulates increased production of abscisic acid (ABA) 89-hydroxylase, catalyzing the conversion of ABA to inactive dihydrophaseic acid (Saika et al, 2007). SUB1A-1 has no effect on this process, as ABA declines similarly in shoots of near isogenic lines that differ in the presence versus absence of SUB1A-1 [M202 and M202(Sub1); Fukao and Bailey-Serres, 2008].…”