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Gibberellin acts through jasmonate to control the expression of MYB21, MYB24, and MYB57 to promote stamen filament growth in Arabidopsis.

Cheng H, Song S, Xiao L, Soo HM, Cheng Z, Xie D, Peng J - PLoS Genet. (2009)

Bottom Line: Further genetic and molecular studies demonstrate that GA suppresses DELLAs to mobilize the expression of the key JA biosynthesis gene DAD1, and this is consistent with the observation that the JA content in the young flower buds of the GA-deficient quadruple mutant ga1-3 gai-t6 rga-t2 rgl1-1 is much lower than that in the WT.We conclude that GA promotes JA biosynthesis to control the expression of MYB21, MYB24, and MYB57.Therefore, we have established a hierarchical relationship between GA and JA in that modulation of JA pathway by GA is one of the prerequisites for GA to regulate the normal stamen development in Arabidopsis.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Proteos, Singapore.

ABSTRACT
Precise coordination between stamen and pistil development is essential to make a fertile flower. Mutations impairing stamen filament elongation, pollen maturation, or anther dehiscence will cause male sterility. Deficiency in plant hormone gibberellin (GA) causes male sterility due to accumulation of DELLA proteins, and GA triggers DELLA degradation to promote stamen development. Deficiency in plant hormone jasmonate (JA) also causes male sterility. However, little is known about the relationship between GA and JA in controlling stamen development. Here, we show that MYB21, MYB24, and MYB57 are GA-dependent stamen-enriched genes. Loss-of-function of two DELLAs RGA and RGL2 restores the expression of these three MYB genes together with restoration of stamen filament growth in GA-deficient plants. Genetic analysis showed that the myb21-t1 myb24-t1 myb57-t1 triple mutant confers a short stamen phenotype leading to male sterility. Further genetic and molecular studies demonstrate that GA suppresses DELLAs to mobilize the expression of the key JA biosynthesis gene DAD1, and this is consistent with the observation that the JA content in the young flower buds of the GA-deficient quadruple mutant ga1-3 gai-t6 rga-t2 rgl1-1 is much lower than that in the WT. We conclude that GA promotes JA biosynthesis to control the expression of MYB21, MYB24, and MYB57. Therefore, we have established a hierarchical relationship between GA and JA in that modulation of JA pathway by GA is one of the prerequisites for GA to regulate the normal stamen development in Arabidopsis.

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JA-Deficiency Specifically Blocks GA-Signaling Leading to the Induction of Expression of MYB21, MYB24, and MYB57.(A–B) Semi-quantitative analysis of MYB21, MYB24, MYB57 (A), GA2ox1, GA3ox1 and GA20ox2 (B) expression in the opr3 mutant flowers at 18, 48, 72 and 96 hrs after GA treatment. Data were averaged from 2–4 batches of independently treated samples and ACTII was used as the normalization control. The graph was drawn based on Log10 scale of the ratio of the expression levels of GA treated versus untreated samples. (C–D) Semi-quantitative analysis of LOX2 (in red line), GA2ox1, GA3ox1 and GA20ox2 (C), MYB21, MYB24 and MYB57 (D) expression in the ga1-3 gai-t6 rga-t2 rgl1-1 (Q3) mutant flowers at 18, 48, 72 and 96 hrs after JA treatment. Data were averaged from 2–4 batches of independently treated samples and ACTII was used as the normalization control. The graph was drawn based on Log10 scale of the ratio of the expression levels of JA treated versus untreated samples.
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pgen-1000440-g005: JA-Deficiency Specifically Blocks GA-Signaling Leading to the Induction of Expression of MYB21, MYB24, and MYB57.(A–B) Semi-quantitative analysis of MYB21, MYB24, MYB57 (A), GA2ox1, GA3ox1 and GA20ox2 (B) expression in the opr3 mutant flowers at 18, 48, 72 and 96 hrs after GA treatment. Data were averaged from 2–4 batches of independently treated samples and ACTII was used as the normalization control. The graph was drawn based on Log10 scale of the ratio of the expression levels of GA treated versus untreated samples. (C–D) Semi-quantitative analysis of LOX2 (in red line), GA2ox1, GA3ox1 and GA20ox2 (C), MYB21, MYB24 and MYB57 (D) expression in the ga1-3 gai-t6 rga-t2 rgl1-1 (Q3) mutant flowers at 18, 48, 72 and 96 hrs after JA treatment. Data were averaged from 2–4 batches of independently treated samples and ACTII was used as the normalization control. The graph was drawn based on Log10 scale of the ratio of the expression levels of JA treated versus untreated samples.

Mentions: We showed in the above that the expression of MYB21, MYB24 and MYB57 was repressed in the ga1-3 gai-t6 rga-t2 rgl1-1 quadruple mutant (wild type for RGL2) but restored to normal in the ga1-3 gai-t6 rga-t2 rgl1-1 rgl2-1 penta mutant (Figure 2A and 2B). Mandaokar et al reported that the expression of MYB21 and MYB24 was downregulated in opr3 mutant and application of exogenous JA could restore their expression [32]. These results suggest that there might be a crosstalk between the GA and JA pathways in regulating the expression of MYB21, MYB24 and MYB57 during stamen development. Genetically, there are three possible ways of interaction between GA and JA. Firstly, GA might act through the JA pathway to regulate the expression of these MYB genes. In this case it is expected that JA application onto ga1-3 gai-t6 rga-t2 rgl1-1 would induce the expression of MYB21, MYB24 and MYB57 whilst GA application onto opr3 would have no effect on their expression. Conversely, JA may act upstream of the GA pathway to regulate the expression of these three MYB genes. In this case, GA application onto opr3 would induce whilst JA application onto ga1-3 gai-t6 rga-t2 rgl1-1 would have no effect on the expression of MYB21, MYB24 and MYB57. The third possibility is that GA and JA may not act in a hierarchical manner but rather via parallel pathways to regulate the expression of the three MYB genes. If this is the case, GA application onto opr3 and JA application onto ga1-3 gai-t6 rga-t2 rgl1-1 would probably both induce the expression of the three MYB genes. To find out which is the likely case, we first examined the effect of GA application on JA-deficient mutant opr3 and found that GA application failed to rescue the opr3 mutant phenotype and failed to induce the expression of MYB21, MYB24 and MYB57 in opr3 even at 96 hrs after GA treatment (Figure 5A). Failure in induction of expression of MYB21, MYB24 and MYB57 in GA-treated opr3 mutants could be due to inactivation of GA signaling in JA-deficient background. GA3ox1 and GA20ox2 are two key genes that contribute to the biosynthesis of bioactive GA and these two genes are under negative feedback regulation by GA signaling pathway (GA-down) [30]. On the other hand, GA2ox1 is a GA-up gene responsible for GA catabolism [30]. Examination of the GA3ox1 and GA20ox2 and GA2ox1 expression in GA-treated opr3 mutants showed expected GA-response (Figure 5B). Meanwhile, expression of GA3ox1 and GA2ox1 appeared normal in opr3 (Figure 6A). These results suggest that JA-deficiency specifically blocks the GA-signaling leading to the induction of MYB21, MYB24 and MYB57 expression but not the negative feedback pathway for GA-biosynthesis.


Gibberellin acts through jasmonate to control the expression of MYB21, MYB24, and MYB57 to promote stamen filament growth in Arabidopsis.

Cheng H, Song S, Xiao L, Soo HM, Cheng Z, Xie D, Peng J - PLoS Genet. (2009)

JA-Deficiency Specifically Blocks GA-Signaling Leading to the Induction of Expression of MYB21, MYB24, and MYB57.(A–B) Semi-quantitative analysis of MYB21, MYB24, MYB57 (A), GA2ox1, GA3ox1 and GA20ox2 (B) expression in the opr3 mutant flowers at 18, 48, 72 and 96 hrs after GA treatment. Data were averaged from 2–4 batches of independently treated samples and ACTII was used as the normalization control. The graph was drawn based on Log10 scale of the ratio of the expression levels of GA treated versus untreated samples. (C–D) Semi-quantitative analysis of LOX2 (in red line), GA2ox1, GA3ox1 and GA20ox2 (C), MYB21, MYB24 and MYB57 (D) expression in the ga1-3 gai-t6 rga-t2 rgl1-1 (Q3) mutant flowers at 18, 48, 72 and 96 hrs after JA treatment. Data were averaged from 2–4 batches of independently treated samples and ACTII was used as the normalization control. The graph was drawn based on Log10 scale of the ratio of the expression levels of JA treated versus untreated samples.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
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pgen-1000440-g005: JA-Deficiency Specifically Blocks GA-Signaling Leading to the Induction of Expression of MYB21, MYB24, and MYB57.(A–B) Semi-quantitative analysis of MYB21, MYB24, MYB57 (A), GA2ox1, GA3ox1 and GA20ox2 (B) expression in the opr3 mutant flowers at 18, 48, 72 and 96 hrs after GA treatment. Data were averaged from 2–4 batches of independently treated samples and ACTII was used as the normalization control. The graph was drawn based on Log10 scale of the ratio of the expression levels of GA treated versus untreated samples. (C–D) Semi-quantitative analysis of LOX2 (in red line), GA2ox1, GA3ox1 and GA20ox2 (C), MYB21, MYB24 and MYB57 (D) expression in the ga1-3 gai-t6 rga-t2 rgl1-1 (Q3) mutant flowers at 18, 48, 72 and 96 hrs after JA treatment. Data were averaged from 2–4 batches of independently treated samples and ACTII was used as the normalization control. The graph was drawn based on Log10 scale of the ratio of the expression levels of JA treated versus untreated samples.
Mentions: We showed in the above that the expression of MYB21, MYB24 and MYB57 was repressed in the ga1-3 gai-t6 rga-t2 rgl1-1 quadruple mutant (wild type for RGL2) but restored to normal in the ga1-3 gai-t6 rga-t2 rgl1-1 rgl2-1 penta mutant (Figure 2A and 2B). Mandaokar et al reported that the expression of MYB21 and MYB24 was downregulated in opr3 mutant and application of exogenous JA could restore their expression [32]. These results suggest that there might be a crosstalk between the GA and JA pathways in regulating the expression of MYB21, MYB24 and MYB57 during stamen development. Genetically, there are three possible ways of interaction between GA and JA. Firstly, GA might act through the JA pathway to regulate the expression of these MYB genes. In this case it is expected that JA application onto ga1-3 gai-t6 rga-t2 rgl1-1 would induce the expression of MYB21, MYB24 and MYB57 whilst GA application onto opr3 would have no effect on their expression. Conversely, JA may act upstream of the GA pathway to regulate the expression of these three MYB genes. In this case, GA application onto opr3 would induce whilst JA application onto ga1-3 gai-t6 rga-t2 rgl1-1 would have no effect on the expression of MYB21, MYB24 and MYB57. The third possibility is that GA and JA may not act in a hierarchical manner but rather via parallel pathways to regulate the expression of the three MYB genes. If this is the case, GA application onto opr3 and JA application onto ga1-3 gai-t6 rga-t2 rgl1-1 would probably both induce the expression of the three MYB genes. To find out which is the likely case, we first examined the effect of GA application on JA-deficient mutant opr3 and found that GA application failed to rescue the opr3 mutant phenotype and failed to induce the expression of MYB21, MYB24 and MYB57 in opr3 even at 96 hrs after GA treatment (Figure 5A). Failure in induction of expression of MYB21, MYB24 and MYB57 in GA-treated opr3 mutants could be due to inactivation of GA signaling in JA-deficient background. GA3ox1 and GA20ox2 are two key genes that contribute to the biosynthesis of bioactive GA and these two genes are under negative feedback regulation by GA signaling pathway (GA-down) [30]. On the other hand, GA2ox1 is a GA-up gene responsible for GA catabolism [30]. Examination of the GA3ox1 and GA20ox2 and GA2ox1 expression in GA-treated opr3 mutants showed expected GA-response (Figure 5B). Meanwhile, expression of GA3ox1 and GA2ox1 appeared normal in opr3 (Figure 6A). These results suggest that JA-deficiency specifically blocks the GA-signaling leading to the induction of MYB21, MYB24 and MYB57 expression but not the negative feedback pathway for GA-biosynthesis.

Bottom Line: Further genetic and molecular studies demonstrate that GA suppresses DELLAs to mobilize the expression of the key JA biosynthesis gene DAD1, and this is consistent with the observation that the JA content in the young flower buds of the GA-deficient quadruple mutant ga1-3 gai-t6 rga-t2 rgl1-1 is much lower than that in the WT.We conclude that GA promotes JA biosynthesis to control the expression of MYB21, MYB24, and MYB57.Therefore, we have established a hierarchical relationship between GA and JA in that modulation of JA pathway by GA is one of the prerequisites for GA to regulate the normal stamen development in Arabidopsis.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Proteos, Singapore.

ABSTRACT
Precise coordination between stamen and pistil development is essential to make a fertile flower. Mutations impairing stamen filament elongation, pollen maturation, or anther dehiscence will cause male sterility. Deficiency in plant hormone gibberellin (GA) causes male sterility due to accumulation of DELLA proteins, and GA triggers DELLA degradation to promote stamen development. Deficiency in plant hormone jasmonate (JA) also causes male sterility. However, little is known about the relationship between GA and JA in controlling stamen development. Here, we show that MYB21, MYB24, and MYB57 are GA-dependent stamen-enriched genes. Loss-of-function of two DELLAs RGA and RGL2 restores the expression of these three MYB genes together with restoration of stamen filament growth in GA-deficient plants. Genetic analysis showed that the myb21-t1 myb24-t1 myb57-t1 triple mutant confers a short stamen phenotype leading to male sterility. Further genetic and molecular studies demonstrate that GA suppresses DELLAs to mobilize the expression of the key JA biosynthesis gene DAD1, and this is consistent with the observation that the JA content in the young flower buds of the GA-deficient quadruple mutant ga1-3 gai-t6 rga-t2 rgl1-1 is much lower than that in the WT. We conclude that GA promotes JA biosynthesis to control the expression of MYB21, MYB24, and MYB57. Therefore, we have established a hierarchical relationship between GA and JA in that modulation of JA pathway by GA is one of the prerequisites for GA to regulate the normal stamen development in Arabidopsis.

Show MeSH
Related in: MedlinePlus