EUI1, Encoding a Putative Cytochrome P450 Monooxygenase, Regulates Internode Elongation by Modulating Gibberellin Responses in Rice

Abstract

Elongation of rice internodes is one of the most important agronomic traits, which determines the plant height and underlies the grain yield. It has been shown that the elongation of internodes is under genetic control, and various factors are implicated in the process. Here, we report a detailed characterization of an elongated uppermost internode1 (eui1) mutant, which has been used in hybrid rice breeding. In the eui1-2 mutant, the cell lengths in the uppermost internodes are significantly longer than that of wild type and thus give rise to the elongated uppermost internode. It was found that the level of active gibberellin was elevated in the mutant, whereas its growth in response to gibberellin is similar to that of the wild type, suggesting that the higher level accumulation of gibberellin in the eui1 mutant causes the abnormal elongation of the uppermost internode. Consistently, the expression levels of several genes which encode gibberellin biosynthesis enzymes were altered. We cloned the EUI1 gene, which encodes a putative cytochrome P450 monooxygenase, by map-based cloning and found that EUI1 was weakly expressed in most tissues, but preferentially in young panicles. To confirm its function, transgenic experiments with different constructs of EUI1 were conducted. Overexpression of EUI1 gave rise to the gibberellin-deficient-like phenotypes, which could be partially reversed by supplementation with gibberellin. Furthermore, apart from the alteration of expression levels of the gibberellin biosynthesis genes, accumulation of SLR1 protein was found in the overexpressing transgenic plants, indicating that the expression level of EUI1 is implicated in both gibberellin-mediated SLR1 destruction and a feedback regulation in gibberellin biosynthesis. Therefore, we proposed that EUI1 plays a negative role in gibberellin-mediated regulation of cell elongation in the uppermost internode of rice.

Gibberellin homeostasis and plant height control by EUI and a role for gibberellin in root gravity responses in rice

“…Likewise, overexpression (OX) of Eui slightly increased SLR1 transcription compared with the WT. In support of our observation, SLR1 protein accumulation or stability was greater in transgenic plants constitutively expressing Eui [19]. By contrast, D1, a positive regulator of GA signaling that encodes the α-subunit of the heterotrimeric G protein [1,2], was not affected ( Figure 4A).…”

“…However, 2-oxidation is not the only mechanism by which bioactive GAs are deactivated. Our previous study has demonstrated that the rice Eui gene (ELONGATED UPPERMOST INTERNODE), also known as Eui1 [19], encodes a novel P450 monooxygenase that catalyzes 16α,17-epoxidation of non-13-hydroxylated GAs to generate bio-inactive 16α,17-[OH] 2 -GAs, representing a novel GA deactivation mechanism in rice [20]. The 16α,17-[OH] 2 -GAs were also found in extracts of other plant species, suggesting that 16α,17-epoxidation might participate in GA deactivation by EUI-related enzymes in a variety of plants [20].…”

Inhibition of Tiller Bud Outgrowth in thetinMutant of Wheat Is Associated with Precocious Internode Development

“…Interestingly, out of the five to six internodes formed at maturity, only the first three basal internodes of tin are solid. In rice, the EUI gene, which encodes a putative cytochrome P450 monooxygenase, controls the length of the uppermost internode (Rutger and Carnahan, 1981;Luo et al, 2006). This shows the presence of independent regulatory mechanisms for the growth of the different internodes in the grasses.…”

Expression of the Nitrate Transporter Gene OsNRT1.1A/OsNPF6.3 Confers High Yield and Early Maturation in Rice

“…To generate the OsNRT1.1A-RNAi vector, a specific sequence of the OsNRT1.1A coding region was amplified. The resulting PCR product was inserted into the pUCC-RNAi vector (Luo et al, 2006) in both sense and antisense orientation and then the fragment containing an artificial inverted-repeat sequence of OsNRT1.1A was transferred into pCAMBIA2301-ACTIN1 for OsNRT1.1A-RNAi construct. All the primers used to generate the overexpression constructs above are listed in Supplemental Table 2, and all of the constructs were confirmed by sequencing.…”