Loss_NN1 of_IO chloroplast_NN1 protease_NN1 SPPA_NN1 function_NN1 alters_VVZ high_JJ light_JJ acclimation_NN1 processes_NN2 in_II Arabidopsis_NP1 thaliana_NN1 L._NP1 (_( Heynh_NP1 ._. )_) 
Abstract_VV0 SPPA1_FO is_VBZ a_AT1 protease_NN1 in_II the_AT plastids_NN2 of_IO plants_NN2 ,_, located_VVN in_II non-appressed_JJ thylakoid_JJ regions_NN2 ._. 
In_II this_DD1 study_NN1 ,_, T-DNA_JJ insertion_NN1 mutants_NN2 of_IO the_AT single-copy_NN1 SPPA1_FO gene_NN1 in_II Arabidopsis_NP1 thaliana_NN1 (_( At1g73990_FO )_) were_VBDR examined_VVN ._. 
Mutation_NN1 of_IO SPPA1_FO had_VHD no_AT effect_NN1 on_II the_AT growth_NN1 and_CC development_NN1 of_IO plants_NN2 under_II moderate_JJ ,_, non-stressful_JJ conditions_NN2 ._. 
It_PPH1 also_RR did_VDD not_XX affect_VVI the_AT quantum_NN1 efficiency_NN1 of_IO photosynthesis_NN1 as_CSA measured_VVN by_II dark-adapted_JJ Fv/Fm_NN1 and_CC light-adapted_JJ FPSII_NN2 ._. 
Chloroplasts_NN2 from_II sppA_NN1 mutants_NN2 were_VBDR indistinguishable_JJ from_II the_AT wild_JJ type_NN1 ._. 
Loss_NN1 of_IO SPPA_NP1 appears_VVZ to_TO affect_VVI photoprotective_JJ mechanisms_NN2 during_II high_JJ light_JJ acclimation_NN1 :_: mutant_NN1 plants_NN2 maintained_VVD a_AT1 higher_JJR level_NN1 of_IO non-photochemical_JJ quenching_NN1 of_IO Photosystem_NP1 II_MC chlorophyll_NN1 (_( NPQ_NP1 )_) than_CSN the_AT wild_JJ type_NN1 ,_, while_CS wild-type_JJ plants_NN2 accumulated_VVD more_DAR anthocyanin_NN1 than_CSN the_AT mutants_NN2 ._. 
The_AT quantum_NN1 efficiency_NN1 of_IO Photosystem_NP1 II_MC was_VBDZ the_AT same_DA in_II all_DB genotypes_NN2 grown_VVN under_II low_JJ light_NN1 ,_, but_CCB was_VBDZ higher_JJR in_II wild_JJ type_NN1 than_CSN mutants_NN2 during_II high_JJ light_JJ acclimation_NN1 ._. 
Further_RRR ,_, the_AT mutants_NN2 retained_VVD the_AT stress-related_JJ Early_JJ Light_JJ Inducible_JJ Protein_NN1 (_( ELIP_NP1 )_) longer_JJR than_CSN wild-type_JJ leaves_NN2 during_II the_AT early_JJ recovery_NN1 period_NN1 after_II acute_JJ high_JJ light_NN1 plus_II cold_JJ treatment_NN1 ._. 
These_DD2 results_NN2 suggest_VV0 that_CST SPPA1_FO may_VM function_VVI during_II high_JJ light_JJ acclimation_NN1 in_II the_AT plastid_NN1 ,_, but_CCB is_VBZ non-essential_JJ for_IF growth_NN1 and_CC development_NN1 under_II non-stress_JJ conditions_NN2 ._. 
Key_JJ words_NN2 :_: Anthocyanin_NP1 ,_, chloroplast_VV0 ,_, high_JJ light_JJ acclimation_NN1 ,_, NPQ_NP1 ,_, protease_VV0 ,_, SPPA_NP1 ._. 
Introduction_NN1 Proteases_NN2 are_VBR essential_JJ for_IF the_AT development_NN1 and_CC function_NN1 of_IO all_DB living_JJ organisms_NN2 ._. 
They_PPHS2 are_VBR responsible_JJ for_IF processing_NN1 ,_, repair_VV0 ,_, and_CC turnover_NN1 of_IO proteins_NN2 and_CC protein_NN1 complexes_NN2 in_II all_DB compartments_NN2 of_IO the_AT organism_NN1 ._. 
Protease_VV0 activity_NN1 is_VBZ tightly_RR controlled_VVN either_RR via_II protease_NN1 expression_NN1 ,_, protease_VV0 activation_NN1 ,_, or_CC substrate_NN1 accessibility_NN1 ._. 
This_DD1 research_NN1 addresses_VVZ the_AT function_NN1 of_IO the_AT plastid_NN1 SPPA1_FO protease_VV0 in_II Arabidopsis_NP1 thaliana_NN1 L._NP1 (_( Heynh_NP1 ._. )_) ._. 
Plastids_NN2 contain_VV0 at_RR21 least_RR22 11_MC types_NN2 of_IO proteases_NN2 (_( Sakamoto_NP1 ,_, 2006_MC )_) ,_, which_DDQ have_VH0 been_VBN identified_VVN by_II biochemical_JJ and_CC genetic_JJ analyses_NN2 ,_, proteomic_JJ analysis_NN1 or_CC by_II prediction_NN1 from_II EST_JJ databases_NN2 and_CC expression_NN1 profiling_VVG (_( reviewed_VVN in_II Adam_NP1 and_CC Clarke_NP1 ,_, 2002_MC ;_; Adam_NP1 et_RA21 al._RA22 ,_, 2006_MC ;_; Sakamoto_NP1 ,_, 2006_MC )_) ._. 
All_DB of_IO the_AT plastid_JJ proteases_NN2 discovered_VVD to_II date_NN1 have_VH0 homologues_NN2 in_II a_AT1 bacterium_NN1 ,_, which_DDQ reflects_VVZ the_AT bacterial_JJ origin_NN1 of_IO the_AT organelle_NN1 (_( Adam_NP1 et_RA21 al._RA22 ,_, 2006_MC )_) ._. 
They_PPHS2 vary_VV0 in_II location_NN1 (_( envelope_NN1 ,_, stroma_NN1 ,_, lumen_NN1 ,_, or_CC thylakoid-localized_JJ )_) and_CC some_DD of_IO their_APPGE functions_NN2 are_VBR known_VVN (_( reviewed_VVN in_II Adam_NP1 and_CC Clarke_NP1 ,_, 2002_MC ;_; Adam_NP1 et_RA21 al._RA22 ,_, 2006_MC ;_; Sakamoto_NP1 ,_, 2006_MC )_) ._. 
Several_DA2 of_IO the_AT best_RRT characterized_VVN plastid_JJ proteases_NN2 are_VBR Clp_NP1 ,_, FtsH_NP1 ,_, Deg_NNU ,_, and_CC CND41_FO ._. 
The_AT SPPA1_FO protease_NN1 is_VBZ always_RR relegated_VVN to_II the_AT heading_NN1 of_IO 'other_NN1 proteases_NN2 '_GE in_II reviews_NN2 on_II the_AT subject_NN1 ,_, along_II21 with_II22 other_JJ proteases_NN2 about_II which_DDQ little_DA1 is_VBZ known_VVN (_( Ostersetzer_NP1 et_RA21 al._RA22 ,_, 2007_MC )_) ._. 
SPPA_NP1 is_VBZ an_AT1 ATP-independent_JJ protease_NN1 IV/serine-type_JJ endopeptidase_NN1 ._. 
It_PPH1 was_VBDZ first_MD described_VVN in_II eubacteria_NN1 where_CS it_PPH1 has_VHZ a_AT1 signal_NN1 peptide_NN1 peptidase_NN1 activity_NN1 ,_, but_CCB is_VBZ also_RR found_VVN in_II viruses_NN2 ,_, archaea_NN1 ,_, and_CC in_II the_AT chloroplasts_NN2 of_IO photoautotrophic_JJ eukaryotes_NN2 (_( reviewed_VVN in_II Sokolenko_NP1 ,_, 2005_MC )_) ._. 
The_AT SPPA_NN1 protease_NN1 family_NN1 contains_VVZ two_MC conserved_VVD potentially_RR catalytic_JJ domains_NN2 ._. 
In_II the_AT cyanobacterium_NN1 Synechocystis_NN1 sp_NNU ._. 
PCC_NP1 6803_MC ,_, and_CC many_DA2 of_IO the_AT other_JJ heterotrophic_JJ and_CC photoautotrophic_JJ bacteria_NN2 ,_, SppA_NP1 has_VHZ several_DA2 isoforms_NN2 that_CST vary_VV0 in_II the_AT number_NN1 of_IO these_DD2 domains_NN2 they_PPHS2 contain_VV0 (_( Sokolenko_NP1 ,_, 2005_MC )_) ._. 
In_II higher_JJR plants_NN2 the_AT two_MC catalytic_JJ domains_NN2 are_VBR retained_VVN in_II a_AT1 single_JJ gene_NN1 ,_, SPPA1_FO (_( hereafter_RT referred_VVN to_II as_CSA SPPA_NP1 )_) ,_, although_CS the_AT structure_NN1 suggests_VVZ that_CST only_RR one_MC1 of_IO the_AT catalytic_JJ domains_NN2 is_VBZ active_JJ (_( Lensch_NP1 et_RA21 al._RA22 ,_, 2001_MC ;_; Sokolenko_NP1 ,_, 2005_MC )_) ._. 
Higher-plant_JJ SPPA_NN1 was_VBDZ first_MD identified_VVN in_II A._NNU thaliana_NN1 (_( Lensch_NP1 et_RA21 al._RA22 ,_, 2001_MC )_) ,_, but_CCB it_PPH1 is_VBZ present_JJ in_II many_DA2 other_JJ species_NN ._. 
NCBI_NP1 Unigene_NP1 currently_RR lists_VVZ SPPA_NN1 genes_NN2 from_II 16_MC plant_NN1 species_NN and_CC the_AT putative_JJ catalytic_JJ sites_NN2 are_VBR conserved_VVN (_( CM_NNU Wetzel_NP1 ,_, data_NN not_XX shown_VVN ;_; Lensch_NP1 et_RA21 al._RA22 ,_, 2001_MC )_) ._. 
This_DD1 indicates_VVZ that_CST SPPA_NP1 is_VBZ ubiquitous_JJ in_II higher_JJR plants_NN2 and_CC is_VBZ conserved_VVN ,_, presumably_RR because_CS it_PPH1 has_VHZ a_AT1 purpose_NN1 ._. 
Its_APPGE function_NN1 in_II chloroplasts_NN2 is_VBZ still_RR unknown_JJ ._. 
Note_VV0 that_CST SPPA1_FO is_VBZ structurally_RR and_CC functionally_RR distinct_JJ from_II SPase1_FO (_( At2g30440_FO ,_, At1g06870_FO ,_, At3g24590_FO )_) ,_, a_AT1 known_JJ plastid_JJ thylakoid_JJ signal_NN1 peptide_NN1 peptidase_NN1 (_( Inoue_NP1 et_RA21 al._RA22 ,_, 2005_MC )_) ._. 
Analysis_NN1 of_IO sppA_NN1 mutant_NN1 responses_NN2 to_II high_JJ light_JJ acclimation_NN1 Wild-type_NN1 and_CC SPPA_NP1 mutant_NN1 plants_NN2 were_VBDR grown_VVN under_II moderately_RR low_JJ light_NN1 (_( LL_NP1 ;_; 120_MC lmol_VV0 m2s1_FO )_) then_RT shifted_VVN to_II higher_JJR light_NN1 (_( HL_NP1 ;_; 850_MC lmol_VV0 m2s1_FO )_) for_IF 7_MC d_ZZ1 ._. 
Standard_JJ measures_NN2 of_IO HL_NP1 acclimation_NN1 in_II plants_NN2 are_VBR a_AT1 loss_NN1 in_II total_JJ chlorophyll_NN1 and_CC a_AT1 shift_NN1 to_II a_AT1 higher_JJR chlorophyll_NN1 a/b_FU ratio_NN1 ,_, which_DDQ indicates_VVZ a_AT1 loss_NN1 of_IO Chl_NP1 b_ZZ1 from_II reduced_JJ antennae_NN2 size_NN1 (_( Yang_NP1 et_RA21 al._RA22 ,_, 1998_MC ;_; Jackowski_NP1 et_RA21 al._RA22 ,_, 2003_MC )_) ._. 
After_II 7_MC d_ZZ1 in_II HL_NP1 all_DB three_MC genotypes_NN2 are_VBR visually_RR indistinguishable_JJ (_( Fig._NN1 4A_FO )_) ._. 
Under_II HL_NP1 they_PPHS2 had_VHD statistically_RR similar_JJ losses_NN2 in_II total_JJ chlorophyll_NN1 &lsqb;_( Fig._NN1 4B_FO ;_; 2-way_JJ ANOVA_NN1 showed_VVD no_AT genotype3light_FO interaction_NN1 ,_, F(2,30)_FO 0.49_MC ,_, P0.61_FO ;_; genotype_NN1 was_VBDZ not_XX a_AT1 significant_JJ source_NN1 of_IO variation_NN1 ,_, F(2,30)_FO 0.96_MC ,_, P0.40_FO ;_; but_CCB light_JJ level_NN1 was_VBDZ a_AT1 significant_JJ source_NN1 of_IO variation_NN1 F(1,30)_FO 8.75_MC ,_, P0.006_FO &rsqb;_) ._. 
They_PPHS2 also_RR had_VHD similar_JJ increases_NN2 in_II chlorophyll_NN1 a/b_FU ratios_NN2 under_II HL_NP1 &lsqb;_( Fig._NN1 4C_FO ;_; 2-way_JJ ANOVA_NN1 showed_VVD no_AT genotype3light_FO interaction_NN1 ,_, F(2,30)_FO 0.58_MC ,_, P0.57_FO ;_; genotype_NN1 was_VBDZ a_AT1 significant_JJ source_NN1 of_IO variation_NN1 ,_, F(2,30)_FO 4.23_MC ,_, P0.03_FO ;_; but_CCB light_JJ level_NN1 accounted_VVN for_IF the_AT greatest_JJT source_NN1 of_IO variation_NN1 F(1,30)_FO 96.67_MC ,_, 
