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The reduced plastid-encoded polymerase-dependent plastid gene expression leads to the delayed greening of the Arabidopsis fln2 mutant.

Huang C, Yu QB, Lv RH, Yin QQ, Chen GY, Xu L, Yang ZN - PLoS ONE (2013)

Bottom Line: This indicates that FLN2 functions in regulation of PEP activity associated with these TAC components. fln2-4 exhibited delayed greening on sucrose-containing medium.Together with the data that FLN1 could interact with itself in yeast, FLN1 may form a homodimer to replace FLN1-FLN2 as the TRX z target in redox pathway for maintaining partial PEP activity in fln2-4.We proposed the partial PEP activity in the fln2 mutant allowed plastids to develop into fully functional chloroplasts when exogenous sucrose was supplied, and finally the mutants exhibited green phenotype.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, College of Life and Environmental Sciences, Shanghai Normal University, Shanghai, P.R. China ; Department of Biology, School of Life Sciences, East China Normal University, Shanghai, P.R. China.

ABSTRACT
In Arabidopsis leaf coloration mutants, the delayed greening phenomenon is common. Nonetheless, the mechanism remains largely elusive. Here, a delayed greening mutant fln2-4 of FLN2 (Fructokinase-Like Protein2) was studied. FLN2 is one component of Transcriptionally Active Chromosome (TAC) complex which is thought to contain the complete plastid-encoded polymerase (PEP). fln2-4 displayed albino phenotype on medium without sucrose. The PEP-dependent plastid gene expression and chloroplast development were inhibited in fln2-4. Besides interacting with thioredoxin z (TRX z), we identified that FLN2 interacted with another two members of TAC complex in yeast including its homologous protein FLN1 (Fructokinase-Like Protein1) and pTAC5. This indicates that FLN2 functions in regulation of PEP activity associated with these TAC components. fln2-4 exhibited delayed greening on sucrose-containing medium. Comparison of the PEP-dependent gene expression among two complete albino mutants (trx z and ptac14), two yellow mutants (ecb2-2 and ys1) and the fln2-4 showed that fln2-4 remains partial PEP activity. FLN2 and FLN1 are the target proteins of TRX z involved in affecting the PEP activity. Together with the data that FLN1 could interact with itself in yeast, FLN1 may form a homodimer to replace FLN1-FLN2 as the TRX z target in redox pathway for maintaining partial PEP activity in fln2-4. We proposed the partial PEP activity in the fln2 mutant allowed plastids to develop into fully functional chloroplasts when exogenous sucrose was supplied, and finally the mutants exhibited green phenotype.

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Comparison of PEP-dependent plastid gene expression between fln2–4 and four leaf coloration mutants.(A) The phenotypes of WT and four leaf coloration mutants grown with or without sucrose. (B) qRT-PCR analysis the transcript levels of four PEP-dependent plastid genes in fln2–4 seedlings and other four leaf coloration mutants grown on MS medium without sucrose for 7 days. These PEP-dependent genes refer to psbA, psbB, psaB, petD. Expression levels are presented as the percentage relative to WT. Data are means ± SD (n = 3). (C) The accumulation of psbA and psbB transcripts detected by Northern blot.
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pone-0073092-g007: Comparison of PEP-dependent plastid gene expression between fln2–4 and four leaf coloration mutants.(A) The phenotypes of WT and four leaf coloration mutants grown with or without sucrose. (B) qRT-PCR analysis the transcript levels of four PEP-dependent plastid genes in fln2–4 seedlings and other four leaf coloration mutants grown on MS medium without sucrose for 7 days. These PEP-dependent genes refer to psbA, psbB, psaB, petD. Expression levels are presented as the percentage relative to WT. Data are means ± SD (n = 3). (C) The accumulation of psbA and psbB transcripts detected by Northern blot.

Mentions: The most distinct characteristic of fln2–4 mutant is its delayed greening phenotype when grown on sucrose-containing medium. We assayed the expression of PEP-dependent plastid genes in fln2–4 during its greening process. Results showed that the transcript levels of the three selected genes (rbcL, psbA, psbB) in 7-day-old fln2–4 mutant were still significantly lower than that in WT. However, after 14 days of growth on sucrose-containing medium, the rbcL mRNA accumulated to similar levels in WT, while the psbB transcription was slightly enhanced (Figure 6). These results indicated that the transcripts of several PEP-dependent genes were able to gradually accumulate during the greening of fln2–4. To disclose whether these differences in plastid gene expression were tightly linked with leaf phenotype, we chose four leaf coloration mutants for further research, which including two complete albino mutants trx z[17] and ptac14[22], and two yellow mutants ecb2–2[27] and ys1[26]. When germinated on MS medium, trx z and ptac14 exhibited albino cotyledons and died before developing true leaves. While grown on MS medium containing 2% sucrose, they could produce pale yellow cotyledons and true leaves (Figure 7A). Nevertheless, these mutants subsequently died. In contrast, the ecb2–2 and ys1 seedlings initially exhibited yellow cotyledons and were able to turn green without exogenous sucrose (Figure 7A). However, the mature ecb2–2 and ys1 plants were slightly weaker than WT (data not shown). We compared the PEP activity in these four leaf coloration mutants (trx z, ptac14, ecb2–2 and ys1) and the fln2–4 through detecting the transcript abundance of four PEP-dependent chloroplast genes (psaB, psbA, psbB and petD). Quantitative Real-Time PCR (qRT-PCR) assay showed that the expression of these genes in the two complete albino mutants (trx z and ptac14) were lower than that in the fln2–4, ecb2–2 and ys1, respectively. In addition, the expression of these genes in the delayed greening fln2–4 mutant was lower than that in the yellow mutant ecb2–2 and ys1 (Figure 7B). Northern blot analysis using probes for psbA and psbB in these mutants exhibited the similar result (Figure 7C). All of these results suggest that the PEP activity in fln2–4 is higher than that in the complete albino mutants but lower than that in the yellow mutants.


The reduced plastid-encoded polymerase-dependent plastid gene expression leads to the delayed greening of the Arabidopsis fln2 mutant.

Huang C, Yu QB, Lv RH, Yin QQ, Chen GY, Xu L, Yang ZN - PLoS ONE (2013)

Comparison of PEP-dependent plastid gene expression between fln2–4 and four leaf coloration mutants.(A) The phenotypes of WT and four leaf coloration mutants grown with or without sucrose. (B) qRT-PCR analysis the transcript levels of four PEP-dependent plastid genes in fln2–4 seedlings and other four leaf coloration mutants grown on MS medium without sucrose for 7 days. These PEP-dependent genes refer to psbA, psbB, psaB, petD. Expression levels are presented as the percentage relative to WT. Data are means ± SD (n = 3). (C) The accumulation of psbA and psbB transcripts detected by Northern blot.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3760890&req=5

pone-0073092-g007: Comparison of PEP-dependent plastid gene expression between fln2–4 and four leaf coloration mutants.(A) The phenotypes of WT and four leaf coloration mutants grown with or without sucrose. (B) qRT-PCR analysis the transcript levels of four PEP-dependent plastid genes in fln2–4 seedlings and other four leaf coloration mutants grown on MS medium without sucrose for 7 days. These PEP-dependent genes refer to psbA, psbB, psaB, petD. Expression levels are presented as the percentage relative to WT. Data are means ± SD (n = 3). (C) The accumulation of psbA and psbB transcripts detected by Northern blot.
Mentions: The most distinct characteristic of fln2–4 mutant is its delayed greening phenotype when grown on sucrose-containing medium. We assayed the expression of PEP-dependent plastid genes in fln2–4 during its greening process. Results showed that the transcript levels of the three selected genes (rbcL, psbA, psbB) in 7-day-old fln2–4 mutant were still significantly lower than that in WT. However, after 14 days of growth on sucrose-containing medium, the rbcL mRNA accumulated to similar levels in WT, while the psbB transcription was slightly enhanced (Figure 6). These results indicated that the transcripts of several PEP-dependent genes were able to gradually accumulate during the greening of fln2–4. To disclose whether these differences in plastid gene expression were tightly linked with leaf phenotype, we chose four leaf coloration mutants for further research, which including two complete albino mutants trx z[17] and ptac14[22], and two yellow mutants ecb2–2[27] and ys1[26]. When germinated on MS medium, trx z and ptac14 exhibited albino cotyledons and died before developing true leaves. While grown on MS medium containing 2% sucrose, they could produce pale yellow cotyledons and true leaves (Figure 7A). Nevertheless, these mutants subsequently died. In contrast, the ecb2–2 and ys1 seedlings initially exhibited yellow cotyledons and were able to turn green without exogenous sucrose (Figure 7A). However, the mature ecb2–2 and ys1 plants were slightly weaker than WT (data not shown). We compared the PEP activity in these four leaf coloration mutants (trx z, ptac14, ecb2–2 and ys1) and the fln2–4 through detecting the transcript abundance of four PEP-dependent chloroplast genes (psaB, psbA, psbB and petD). Quantitative Real-Time PCR (qRT-PCR) assay showed that the expression of these genes in the two complete albino mutants (trx z and ptac14) were lower than that in the fln2–4, ecb2–2 and ys1, respectively. In addition, the expression of these genes in the delayed greening fln2–4 mutant was lower than that in the yellow mutant ecb2–2 and ys1 (Figure 7B). Northern blot analysis using probes for psbA and psbB in these mutants exhibited the similar result (Figure 7C). All of these results suggest that the PEP activity in fln2–4 is higher than that in the complete albino mutants but lower than that in the yellow mutants.

Bottom Line: This indicates that FLN2 functions in regulation of PEP activity associated with these TAC components. fln2-4 exhibited delayed greening on sucrose-containing medium.Together with the data that FLN1 could interact with itself in yeast, FLN1 may form a homodimer to replace FLN1-FLN2 as the TRX z target in redox pathway for maintaining partial PEP activity in fln2-4.We proposed the partial PEP activity in the fln2 mutant allowed plastids to develop into fully functional chloroplasts when exogenous sucrose was supplied, and finally the mutants exhibited green phenotype.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, College of Life and Environmental Sciences, Shanghai Normal University, Shanghai, P.R. China ; Department of Biology, School of Life Sciences, East China Normal University, Shanghai, P.R. China.

ABSTRACT
In Arabidopsis leaf coloration mutants, the delayed greening phenomenon is common. Nonetheless, the mechanism remains largely elusive. Here, a delayed greening mutant fln2-4 of FLN2 (Fructokinase-Like Protein2) was studied. FLN2 is one component of Transcriptionally Active Chromosome (TAC) complex which is thought to contain the complete plastid-encoded polymerase (PEP). fln2-4 displayed albino phenotype on medium without sucrose. The PEP-dependent plastid gene expression and chloroplast development were inhibited in fln2-4. Besides interacting with thioredoxin z (TRX z), we identified that FLN2 interacted with another two members of TAC complex in yeast including its homologous protein FLN1 (Fructokinase-Like Protein1) and pTAC5. This indicates that FLN2 functions in regulation of PEP activity associated with these TAC components. fln2-4 exhibited delayed greening on sucrose-containing medium. Comparison of the PEP-dependent gene expression among two complete albino mutants (trx z and ptac14), two yellow mutants (ecb2-2 and ys1) and the fln2-4 showed that fln2-4 remains partial PEP activity. FLN2 and FLN1 are the target proteins of TRX z involved in affecting the PEP activity. Together with the data that FLN1 could interact with itself in yeast, FLN1 may form a homodimer to replace FLN1-FLN2 as the TRX z target in redox pathway for maintaining partial PEP activity in fln2-4. We proposed the partial PEP activity in the fln2 mutant allowed plastids to develop into fully functional chloroplasts when exogenous sucrose was supplied, and finally the mutants exhibited green phenotype.

Show MeSH
Related in: MedlinePlus