The conserved GATA transcription factor Cga1 (Os02g12790) regulates chloroplast development and plant architecture. Strong overexpression of Cga1 produces dark green, semidwarf plants with reduced tillering, whereas RNA interference knockdown results in reduced chlorophyll and increased tillering. Coexpression, microarray, and real-time expression analyses demonstrate a correlation between Cga1 expression and the expression of important nucleus-encoded, chloroplast-localized genes. Constitutive Cga1 overexpression increases both chloroplast biogenesis and starch production but also results in delayed senescence and reduced grain filling. It is one of transcription factors of the GATA family with a significant degree of conservation in the dicot model organism Arabidopsis.
Transgenic Arabidopsis plants with altered expression of CGA1 have been shown to exhibit differences in germination, chlorophyll content, chloroplast number, leaf size, flowering time, senescence and chloroplast biogenesis in cells.
Transgenic rice with altered expression of Cga1 exhibits differences in chlorophyll, chloroplast number, and starch content, which has also been reported in Arabidopsis. However, we also observed a dosage-dependent influence on phenotype, with strong overexpression causing a semidwarf phenotype, similar to the GA mutant Green Revolution varieties (Figure1).
Figure 1. Transgenic modification to Cga1 expression alters chlorophyll content and plant architecture.Transgenic modification to Cga1 expression alters chlorophyll content and plant architecture. A, Expression of Cga1 in the selected transgenic lines compared with wild-type Kaybonnet controls (Wt-Kay) measured using qRT-PCR. B, Preflowering transgenic OsCga1 lines at 60 d after germination exhibit differences in plant architecture. C, Chlorophyll at young (third leaf) and late (flag leaf) stages of development (n = 36+; *P < 0.05). D, Height of mature transgenic plants (n = 40; *P > 0.05). E, Mature transgenic plants (150 d after germination) compared with the wild type. F, Number of flowering tillers (n = 80; *P < 0.05).
Novel evidence was presented that altering Cga1 expression in rice significantly influences tillering, biomass, and yield (Figure1, 2).
Figure 2. Cga1 expression influences starch content and grain production.Cga1 expression influences starch content and grain production. A, Light microscopy of leaf blades showing fresh samples (right) and following IKI staining (left) for starch. B, Wax-embedded leaf tissue sections (12 μm) stained with IKI. C, Seed starch measured using the Megazyme Total Starch kit (Wilcoxon; n = 5–6; *P< 0.05). D, Seed mass (n = 100; *P> 0.05) and images of seeds produced from transgenic lines. E, Panicles from the primary tiller showing differences in architecture as well as delayed senescence of Cga1 overexpression lines compared with the wild-type Kaybonnet control (Wt-Kay). F, Panicle architecture and grain filling in the Cga1 transgenics compared with the wild type (n = 40+; *P< 0.05). All data are means±SD.
Changes are demonstrated in the expression of important nucleus-encoded, chloroplast-localized genes involved in chlorophyll binding, photosynthesis, and amino acid and starch biosynthesis in the Cga1 transgenics.
Altering expression of the rice homolog to the FILAMENTOUS TEMPERATURE SENSITIVE-Z (FtsZ) gene involved in chloroplast division provides a potential mechanism for controlling chloroplast number.
Growing the transgenic lines under different N conditions indicates that Cga1 is able to maintain chloroplast development under reduced N conditions, leading to an increased harvest index despite reduced plant size.
Rice tissues and patterns of expression for Cga1 were analyzed and established in wild-type Kaybonnet rice. Cga1 exhibited the strongest expression in green leaf tissue, with little and no expression in roots and floral organs, respectively (Figure3A).
The expression of Cga1 following a number of treatments was also analyzed. Differences in Cga1 expression throughout the course of the day was also observed. (Figure3B). Light was found to significantly increase Cga1 expression, whereas periods of darkness reduced expression (Figure3, B and C). Cga1 was highly upregulated (approximately 5-fold) by the synthetic cytokinin benzyladenine (BA; figure3C). Nitrate (NO3 -) also significantly increased Cga1 expression, although to a lesser extent than BA (Figure3C).
Figure 3. Expression of rice Cga1(Os02g12790).Expression of rice Cga1 (Os02g12790). A, Expression of Cga1 in selected rice tissues. B, Expression of Cga1 at 6-h intervals throughout the course of the day (long day; 16 h of light). C, Real-time PCR of OsCga1 expression levels following periods of darkness or light and following treatment with 10 mM nitrate, 10 μmol of BA cytokinin, or 10 μmol of GA3.
Labs working on this gene
Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
Syngenta Biotechnology, Inc., Research Triangle Park, North Carolina, America
Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut, America
Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, America
Department of Biology, Colorado State University, Fort Collins, America
Department of Biology, University of North Carolina, Chapel Hill, North Carolina, America
Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Japan
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