Os04g0522500

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Annotated Information

Function

The severe dwarf mutant M47191, designated as GA2ox6ACT,carries a T-DNA insertion at a position 2.1 kb upstream of the translation start codon of GA2ox6 (Figure 5C). Accumulation of GA2ox6 mRNA was significantly enhanced by T-DNA activation tagging, and a severe dwarf phenotype was observed in both heterozygous and homozygous mutants. The GA2ox6ACT heterozygous mutant produced seeds with an average fertility of only 43% of the wild type after >5 months of cultivation (Table 1).Other traits significantly altered in the severe dwarf GA2ox6ACT mutant included shorter leaves, later heading date, reduced panicle length, higher tiller numbers, lower grain weight, and lower seed fertility compared with the wild type (Table 1). Germination of GA2ox6ACT seeds was also significantly delayed, as it took 20 d to reach 90% germination rate, while the wild-type and GA2ox9ACT mutant seeds took only 2 d to reach a germination rate of 97 and 98%, respectively (Figure 6C).

'Figure 5. Severely Dwarfed and Semidwarfed Rice Mutants Obtained by T-DNA Activation Tagging.(C) The severe dwarf mutant GA2ox6ACT (M47191).'

'Figure 6. Overexpression of GA2oxs Has Different Effects on Rice Seed Germination and Seedling Growth.(C) Germination rate was normal for the GA2ox9ACT mutant, slightly delayed for the GA2ox5D335-341ACT mutant, and significantly delayed for the GA2ox6ACT mutant compared with the wild type. Numbers of seeds for determining germination rates were 154, 50, 156, and 49 for the wild type, GA2ox5D335-341ACT, GA2ox6ACT, and GA2ox9ACT, respectively.'

Expression

GA2ox6, its mRNAs accumulated in leaves after the phase transition from vegetative to reproductive growth. GA2ox6 mRNA could also be detected in leaves at early seedling stage and transiently at high level during the active tillering stage.Since expression of most GA2oxs terminated after the active tillering stage, the pattern of tiller growth throughout the rice life cycle was examined. Tiller number increased from 30 to 50 DAI (active tillering), remained constant until 75 DAI, and then increased again until 90 DAI (late tillering)when the experiment was terminated (Figure 3C). Expression of each group of GA2oxs paralleled the active and late tillering stages (cf. Figures 3B with 3C).Germination was observed from 1 DAI and reached almost 100% at 2 DAI (Figure 4A). Total RNA was isolated from embryos after imbibition of seeds, and temporal expression profiles of six GA2oxs were analyzed by RT-PCR. The accumulation of most GA2ox mRNAs was detectable starting from 0 to 1 DAI and maintained at similar levels afterward, GA2ox6 had a distinct expression pattern, as its mRNA quickly accumulated from 0.5 to 1 DAI and then decreased significantly from 2 to 4 DAI.

'Figure 3. Differential Expression of Two Groups of GA2oxs Regulates Flower and Tiller Development.(B) Temporal expression patterns of GA2oxs in rice. The last fully expanded leaves were collected from rice plants at different developmental stages. Total RNA was isolated and analyzed by RT-PCR using GA2ox and GA3ox2 gene-specific primers (see Supplemental Table 4 online). The 18S rRNA gene (rRNA) was used as a control.'

'Figure 4. C20 GA2oxs Could Be Responsible for Regulating Seed Germination.(B) Expression patterns of GA2oxs in rice seedlings between 0 and ;5 DAI. Total RNA was isolated from embryos at each time point and analyzed by RT-PCR. The 18S rRNA gene (rRNA) was used as a control.'

'Figure 3. Differential Expression of Two Groups of GA2oxs Regulates Flower and Tiller Development.(C) Tiller development during the life cycle of rice. A total of eight plants were used for counting tiller number, and error bars indicate the SE of the mean at each time point.'

'Figure 4. C20 GA2oxs Could Be Responsible for Regulating Seed Germination.(A) Germination rate of rice seeds reached 100% at 2 DAI.'

Evolution

'Figure 2. Phylogenetic Tree Based on the Comparison of Plant GA2oxs.Amino acid sequences of 29 GA2oxs from nine plant species (see Supplemental Table 3 online). Plant species: At, Arabidopsis thaliana;Cm, Cucurbita maxima; Ls, Lactuca sativa; Nt, Nicotiana sylvestris; Pc,Phaseolus coccineus; PaPt, Populus alba 3 P. tremuloides; Ps, Pisum sativum; So, Spinacia oleracea. The scale value of 0.1 indicates 0.1 amino acid substitutions per site.'

Labs working on this gene

• Institute of Molecular Biology, National Chung-Hsing University, Taichung 402, Taiwan, Republic of China
• Institute of Molecular Biology, Academia Sinica, Taipei 115, Taiwan, Republic of China
• Institute of Plant and Microbial Biology, Academia Sinica, Taipei 115, Taiwan, Republic of China
• Department of Energy Plant Research Laboratory and Department of Plant Biology, Michigan State University,East Lansing, Michigan 48824-1312

References

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