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A High Temperature-Dependent Mitochondrial Lipase EXTRA GLUME1 Promotes Floral Phenotypic Robustness against Temperature Fluctuation in Rice (Oryza sativa L.).

Zhang B, Wu S, Zhang Y, Xu T, Guo F, Tang H, Li X, Wang P, Qian W, Xue Y - PLoS Genet. (2016)

Bottom Line: In this study, we found that eg1 (extra glume1) mutants of rice (Oryza savita L.) showed floral phenotypic variations in different growth locations resulting in a breakdown of floral identity robustness.Furthermore, we found that numerous environmentally responsive genes including many floral identity genes are transcriptionally repressed in eg1 mutants and OsMADS1, OsMADS6 and OsG1 genetically act downstream of EG1 to maintain floral robustness.Collectively, our results demonstrate that EG1 promotes floral robustness against temperature fluctuation by safeguarding the expression of floral identify genes through a high temperature-dependent mitochondrial lipid pathway and uncovers a novel mechanistic insight into floral developmental control.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences and National Center for Plant Gene Research, Beijing, the People's Republic of China.

ABSTRACT
The sessile plants have evolved diverse intrinsic mechanisms to control their proper development under variable environments. In contrast to plastic vegetative development, reproductive traits like floral identity often show phenotypic robustness against environmental variations. However, it remains obscure about the molecular basis of this phenotypic robustness. In this study, we found that eg1 (extra glume1) mutants of rice (Oryza savita L.) showed floral phenotypic variations in different growth locations resulting in a breakdown of floral identity robustness. Physiological and biochemical analyses showed that EG1 encodes a predominantly mitochondria-localized functional lipase and functions in a high temperature-dependent manner. Furthermore, we found that numerous environmentally responsive genes including many floral identity genes are transcriptionally repressed in eg1 mutants and OsMADS1, OsMADS6 and OsG1 genetically act downstream of EG1 to maintain floral robustness. Collectively, our results demonstrate that EG1 promotes floral robustness against temperature fluctuation by safeguarding the expression of floral identify genes through a high temperature-dependent mitochondrial lipid pathway and uncovers a novel mechanistic insight into floral developmental control.

No MeSH data available.


Related in: MedlinePlus

High temperature-dependent manner of EG1 in floral robustness regulation.(a) RT-qPCR analysis of EG1 expression induced by high temperatures in two wild-types. Values are means ± SE (n = 3), and significant difference was determined by ANOVA, *P < 0.05, **P < 0.01, and rice α-TUBULIN as the reference. (b) Western blot analysis of FLAG-EG1 protein accumulation under different temperatures and different tissues in the EG1 complementation lines for 24 hr. Cp, Complementation lines; Ct, non-transgenic wild-type control. HC, Heavy chain of IgG; NS, Nonspecific band (as a loading control). (c) Temperature-dependent lipase activity of EG1. EG1 (Full) and EG1 (Δ45) respectively refer to full-length and no N-terminal (45 AA) protein of EG1 fused to SUMO peptide. Values are means ± SE for three independent experiments. (d) Floral phenotypes of eg1 mutants in a condition of 40°C light 12 hr / 30°C dark 12 hr. Spikelets of eg1-1 with pl, eg and rs phenotypes are shown on i, ii and iii, respectively. Spikelets of eg1-2 with eg and pl phenotypes are shown on iv and v, and with multilayer lemma-like glumes (lel) and/or undetermined inflorescences primordia are on vi to x. x is the inside of ix. le, lemma; pl, palea-lemma mosaic organ; eg, empty glume; lel, lemma-like organ; pa, palea; st, stamen; if, inflorescence primordia. Bars = 2 mm.
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pgen.1006152.g005: High temperature-dependent manner of EG1 in floral robustness regulation.(a) RT-qPCR analysis of EG1 expression induced by high temperatures in two wild-types. Values are means ± SE (n = 3), and significant difference was determined by ANOVA, *P < 0.05, **P < 0.01, and rice α-TUBULIN as the reference. (b) Western blot analysis of FLAG-EG1 protein accumulation under different temperatures and different tissues in the EG1 complementation lines for 24 hr. Cp, Complementation lines; Ct, non-transgenic wild-type control. HC, Heavy chain of IgG; NS, Nonspecific band (as a loading control). (c) Temperature-dependent lipase activity of EG1. EG1 (Full) and EG1 (Δ45) respectively refer to full-length and no N-terminal (45 AA) protein of EG1 fused to SUMO peptide. Values are means ± SE for three independent experiments. (d) Floral phenotypes of eg1 mutants in a condition of 40°C light 12 hr / 30°C dark 12 hr. Spikelets of eg1-1 with pl, eg and rs phenotypes are shown on i, ii and iii, respectively. Spikelets of eg1-2 with eg and pl phenotypes are shown on iv and v, and with multilayer lemma-like glumes (lel) and/or undetermined inflorescences primordia are on vi to x. x is the inside of ix. le, lemma; pl, palea-lemma mosaic organ; eg, empty glume; lel, lemma-like organ; pa, palea; st, stamen; if, inflorescence primordia. Bars = 2 mm.

Mentions: The dependence of the eg1 floral plasticity on environmental temperature raised a possibility that either EG1 or its product or both are likewise regulated by temperature. To examine these possibilities, some heat/cold responsive cis-elements were discovered in the 2 kb genomic sequence upstream of the start codon of EG1 (S3 Table), implying that its expression could be induced by extreme temperatures. To examine this possibility, one-week wild-type seedlings were treated under different temperatures and the EG1 transcript was found to accumulate gradually, to an extremely high extent under heat shock (42°C) as well as usual high temperature 35°C for rice (Fig 5A), but to some extent suppressed under cold stress (4°C) (S7A Fig), indicating the high temperature-induced expression of EG1. A similar result was obtained by using young inflorescences in which EG1 has a high expression (S7B Fig). To examine whether EG1 protein was also influenced by high temperatures, accumulation of FLAG-EG1 fusion protein in eg1-2 complementation lines, with a temperature-insensitive promoter (S7C and S7E Fig), was detected under different temperatures and found it was significantly induced at extreme high temperature 42°C than 25°C and 35°C (Fig 5B and S7D Fig), indicating a stabilization of EG1 protein under heat stress. Furthermore, we detected that lipase activity of EG1 fusion proteins increase as temperature rising (Fig 5C), consistent with the assumption of EG1’s function required under high temperatures. Additionally, we also examined the effect of high temperatures on EG1 subcellular localization, and found no obvious translocation in protoplast system (S8A Fig), while failed to detect EG1 protein in the subcellular fractions of complementation lines except under heat stress for its minute amount (S8B Fig), suggesting that temperature does not significantly influence the subcellular localization of EG1. The increased the transcriptional level, protein stability and lipase activity of EG1 under high temperatures, implying its more significant role under high temperatures. To verify this hypothesis, we observed the floral phenotypes of eg1 mutants under extremely high temperatures and found much severer spikelets in eg1 mutants especially in eg1-2, with multilayer lemma-like organs and undetermined inflorescence meristem, which have never been found in other temperature conditions (Fig 5D), showing a more significant function of EG1 at higher temperatures in floral robustness. eg1 was also found to grow faster than wild-type during primary growing days [54], and we detected this phenotype was much severer under extremely high temperature than others compared with wild-type, which was consistent with the floral phenotype (S9 Fig). Therefore, we concluded that EG1 functions in a high temperature-dependent manner to regulate the floral robustness.


A High Temperature-Dependent Mitochondrial Lipase EXTRA GLUME1 Promotes Floral Phenotypic Robustness against Temperature Fluctuation in Rice (Oryza sativa L.).

Zhang B, Wu S, Zhang Y, Xu T, Guo F, Tang H, Li X, Wang P, Qian W, Xue Y - PLoS Genet. (2016)

High temperature-dependent manner of EG1 in floral robustness regulation.(a) RT-qPCR analysis of EG1 expression induced by high temperatures in two wild-types. Values are means ± SE (n = 3), and significant difference was determined by ANOVA, *P < 0.05, **P < 0.01, and rice α-TUBULIN as the reference. (b) Western blot analysis of FLAG-EG1 protein accumulation under different temperatures and different tissues in the EG1 complementation lines for 24 hr. Cp, Complementation lines; Ct, non-transgenic wild-type control. HC, Heavy chain of IgG; NS, Nonspecific band (as a loading control). (c) Temperature-dependent lipase activity of EG1. EG1 (Full) and EG1 (Δ45) respectively refer to full-length and no N-terminal (45 AA) protein of EG1 fused to SUMO peptide. Values are means ± SE for three independent experiments. (d) Floral phenotypes of eg1 mutants in a condition of 40°C light 12 hr / 30°C dark 12 hr. Spikelets of eg1-1 with pl, eg and rs phenotypes are shown on i, ii and iii, respectively. Spikelets of eg1-2 with eg and pl phenotypes are shown on iv and v, and with multilayer lemma-like glumes (lel) and/or undetermined inflorescences primordia are on vi to x. x is the inside of ix. le, lemma; pl, palea-lemma mosaic organ; eg, empty glume; lel, lemma-like organ; pa, palea; st, stamen; if, inflorescence primordia. Bars = 2 mm.
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Related In: Results  -  Collection

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pgen.1006152.g005: High temperature-dependent manner of EG1 in floral robustness regulation.(a) RT-qPCR analysis of EG1 expression induced by high temperatures in two wild-types. Values are means ± SE (n = 3), and significant difference was determined by ANOVA, *P < 0.05, **P < 0.01, and rice α-TUBULIN as the reference. (b) Western blot analysis of FLAG-EG1 protein accumulation under different temperatures and different tissues in the EG1 complementation lines for 24 hr. Cp, Complementation lines; Ct, non-transgenic wild-type control. HC, Heavy chain of IgG; NS, Nonspecific band (as a loading control). (c) Temperature-dependent lipase activity of EG1. EG1 (Full) and EG1 (Δ45) respectively refer to full-length and no N-terminal (45 AA) protein of EG1 fused to SUMO peptide. Values are means ± SE for three independent experiments. (d) Floral phenotypes of eg1 mutants in a condition of 40°C light 12 hr / 30°C dark 12 hr. Spikelets of eg1-1 with pl, eg and rs phenotypes are shown on i, ii and iii, respectively. Spikelets of eg1-2 with eg and pl phenotypes are shown on iv and v, and with multilayer lemma-like glumes (lel) and/or undetermined inflorescences primordia are on vi to x. x is the inside of ix. le, lemma; pl, palea-lemma mosaic organ; eg, empty glume; lel, lemma-like organ; pa, palea; st, stamen; if, inflorescence primordia. Bars = 2 mm.
Mentions: The dependence of the eg1 floral plasticity on environmental temperature raised a possibility that either EG1 or its product or both are likewise regulated by temperature. To examine these possibilities, some heat/cold responsive cis-elements were discovered in the 2 kb genomic sequence upstream of the start codon of EG1 (S3 Table), implying that its expression could be induced by extreme temperatures. To examine this possibility, one-week wild-type seedlings were treated under different temperatures and the EG1 transcript was found to accumulate gradually, to an extremely high extent under heat shock (42°C) as well as usual high temperature 35°C for rice (Fig 5A), but to some extent suppressed under cold stress (4°C) (S7A Fig), indicating the high temperature-induced expression of EG1. A similar result was obtained by using young inflorescences in which EG1 has a high expression (S7B Fig). To examine whether EG1 protein was also influenced by high temperatures, accumulation of FLAG-EG1 fusion protein in eg1-2 complementation lines, with a temperature-insensitive promoter (S7C and S7E Fig), was detected under different temperatures and found it was significantly induced at extreme high temperature 42°C than 25°C and 35°C (Fig 5B and S7D Fig), indicating a stabilization of EG1 protein under heat stress. Furthermore, we detected that lipase activity of EG1 fusion proteins increase as temperature rising (Fig 5C), consistent with the assumption of EG1’s function required under high temperatures. Additionally, we also examined the effect of high temperatures on EG1 subcellular localization, and found no obvious translocation in protoplast system (S8A Fig), while failed to detect EG1 protein in the subcellular fractions of complementation lines except under heat stress for its minute amount (S8B Fig), suggesting that temperature does not significantly influence the subcellular localization of EG1. The increased the transcriptional level, protein stability and lipase activity of EG1 under high temperatures, implying its more significant role under high temperatures. To verify this hypothesis, we observed the floral phenotypes of eg1 mutants under extremely high temperatures and found much severer spikelets in eg1 mutants especially in eg1-2, with multilayer lemma-like organs and undetermined inflorescence meristem, which have never been found in other temperature conditions (Fig 5D), showing a more significant function of EG1 at higher temperatures in floral robustness. eg1 was also found to grow faster than wild-type during primary growing days [54], and we detected this phenotype was much severer under extremely high temperature than others compared with wild-type, which was consistent with the floral phenotype (S9 Fig). Therefore, we concluded that EG1 functions in a high temperature-dependent manner to regulate the floral robustness.

Bottom Line: In this study, we found that eg1 (extra glume1) mutants of rice (Oryza savita L.) showed floral phenotypic variations in different growth locations resulting in a breakdown of floral identity robustness.Furthermore, we found that numerous environmentally responsive genes including many floral identity genes are transcriptionally repressed in eg1 mutants and OsMADS1, OsMADS6 and OsG1 genetically act downstream of EG1 to maintain floral robustness.Collectively, our results demonstrate that EG1 promotes floral robustness against temperature fluctuation by safeguarding the expression of floral identify genes through a high temperature-dependent mitochondrial lipid pathway and uncovers a novel mechanistic insight into floral developmental control.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences and National Center for Plant Gene Research, Beijing, the People's Republic of China.

ABSTRACT
The sessile plants have evolved diverse intrinsic mechanisms to control their proper development under variable environments. In contrast to plastic vegetative development, reproductive traits like floral identity often show phenotypic robustness against environmental variations. However, it remains obscure about the molecular basis of this phenotypic robustness. In this study, we found that eg1 (extra glume1) mutants of rice (Oryza savita L.) showed floral phenotypic variations in different growth locations resulting in a breakdown of floral identity robustness. Physiological and biochemical analyses showed that EG1 encodes a predominantly mitochondria-localized functional lipase and functions in a high temperature-dependent manner. Furthermore, we found that numerous environmentally responsive genes including many floral identity genes are transcriptionally repressed in eg1 mutants and OsMADS1, OsMADS6 and OsG1 genetically act downstream of EG1 to maintain floral robustness. Collectively, our results demonstrate that EG1 promotes floral robustness against temperature fluctuation by safeguarding the expression of floral identify genes through a high temperature-dependent mitochondrial lipid pathway and uncovers a novel mechanistic insight into floral developmental control.

No MeSH data available.


Related in: MedlinePlus