Os04g0169100

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Annotated Information

Function

• In rice, ETR2 reduces ethylene sensitivity, delays the transition fromthe vegetative stage to the floral stage, and affects starch accumulation.

Overexpression

• To study the roles of ETR2 in rice growth and development, we made two constructs, pBIN438-OsETR2 and pZH01-OsETR2- RNAi, and transferred them into rice (TP309) via Agrobacterium tumefaciens–mediated transformation. The pBIN438-OsETR2 construct harbored the full-length genomic gene of ETR2 under the control of the double 35S promoter with an enhancer. The pZH01-OsETR2-RNAi construct contained two inverted repeats of the partial ETR2 gene and was used for inhibiting ETR2 gene expression (Figure 3A). Forty-one T0 overexpression lines and 20 T0 RNAi lines were obtained.

• The researchers analyzed the response of the transgenic seedlings upon 1-aminocyclopropane- 1-caroxylic acid (ACC; ethylene biosynthesis precursor) treatment. Root growth of etiolated wild-type rice seedlings (wild type) was inhibited in response to increasing concentrations of ACC, whereas shoot growth was not significantly affected (Figure 3C). In the four lines overexpressing ETR2, root lengths were only mslightly reduced upon ACC treatment compared with the corresponding wild-type controls (Figure 3C, top and bottom left panels). In the two RNAi lines with reduced ETR2 expression, root lengths were similar to that of the wild-type plants in response to ACC treatment (Figure 3C, top and bottom right panels). Shoot lengths of the overexpression lines and the RNAi lines were not significantly different from those of the wild-type controls (Figure 3C, top panels). These results indicate that rice roots are more sensitive to ACC treatment than are rice shoots and that overexpression of ETR2 conferred reduced ethylene sensitivity in transgenic rice plants. Partial reduction of the ETR2 level had limited effects on ethylene sensitivity.
• The researchers examined the sensitivity of the transgenic rice plants to ethylene by testing for the promotion of coleoptile growth. At higher ethylene concentrations (50 ppm), the transgenic plants overexpressing ETR2 exhibited significantly shorter coleoptiles than wild-type plants (Figure 3D), indicating that overexpression of ETR2 conferred reduced ethylene sensitivity in the regulation of coleoptile growth. The RNAi plants showed no significant changes in coleoptile length in comparison with the wild-type plants.

Figure 3. Ethylene Sensitivity of ETR2 Transgenic Rice Plants. .

Expression

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Evolution

• The rice ETR2 kinase domain was compared with those from other ethylene receptors or homologs (Figure 1). Alignment of the amino acid sequences of the ethylene receptor kinase domains of various ethylene recpetors. The positions of the H, N, G1, F, and G2 box are indicated on top of the sequence based on the corresponding boxes from Arabidopsis ETR1. The amino acids shaded in black are identical to each other. Five mutated amino acids (G to A, E to Q, R to Q, F to A, and G to A) upstream of and within the N box are also indicated, and the mutated protein N was used for kinase analysis in Figure 2. At ETR1, At ETR2, and At EIN4 are from Arabidopsis. NTHK1 and NTHK2 are from tobacco. Zm ETR2 is from maize. The Os ETR2/Os PK1, Os ETR3/Os PK2, and Os ETR4/Os PK3 receptors are from rice.

Figure 1. Alignment of the Amino Acid Sequence of the Kinase Domain with That of Other Ethylene Receptors. .

Labs working on this gene

• Plant Gene Research Center, National Key Lab of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China