Abstract
COMATOSE (CTS) encodes a peroxisomal ATP-binding cassette transporter required not only for beta-oxidation of storage lipids during germination and establishment, but also for biosynthesis of jasmonic acid and conversion of indole butyric acid to indole acetic acid. cts mutants exhibited reduced fertilization, which was rescued by genetic complementation, but not by exogenous application of jasmonic acid or indole acetic acid. Reduced fertilization was also observed in thiolase (kat2-1) and peroxisomal acyl-Coenzyme A synthetase mutants (lacs6-1,lacs7-1), indicating a general role for beta-oxidation in fertility. Genetic analysis revealed reduced male transmission of cts alleles and both cts pollen germination and tube growth in vitro were impaired in the absence of an exogenous carbon source. Aniline blue staining of pollinated pistils demonstrated that pollen tube growth was affected only when both parents bore the cts mutation, indicating that expression of CTS in either male or female tissues was sufficient to support pollen tube growth in vivo. Accordingly, abundant peroxisomes were detected in a range of maternal tissues. Although gamma-aminobutyric acid levels were reduced in flowers of cts mutants, they were unchanged in kat2-1, suggesting that alterations in gamma-aminobutyric acid catabolism do not contribute to the reduced fertility phenotype through altered pollen tube targeting. Taken together, our data support an important role for beta-oxidation in fertility in Arabidopsis (Arabidopsis thaliana) and suggest that this pathway could play a role in the mobilization of lipids in both pollen and female tissues.
Highlights
COMATOSE(CTS; known as PEROXISOME DEFECTIVE[SPED3]and A. thalianaPEROXISOMAL ABC TRANSPORTER[1AtPXAl]) encodes a peroxisomal ATP-bindingcassette transporter,which was identified in a genetic screen for positive regulators of germination(Russellet al.,2000).cts-1mutantseeds cannotgerminatein theabsenceof classicaldormancybreakingtreatmentsand do not establish in the absence of an exogenous energy source because of theirinabilityto mobilizestoragelipidsby /3-oxidation (Footittet al., 2002,2006).Mutantcts alleles have been identified in screens for seedlings resistant to 2,4-dichlorophenoxybutyricacid and indole butyric acid (IBA;Zolman et al, 2001;Hayashi et al, 2002)
Abundantperoxisomeswere detectedin a rangeof maternaltissues.Althoughy-aminobutyricacid levels were reducedin flowersof cts mutants,they were unchanged in katl-1,suggestingthat alterationsin y-aminobutyricacid catabolismdo not contributeto the reduced fertilityphenotype throughaltered pollen tube targeting.Takentogether,our data support an importantrole for /3-oxidationin fertility in Arabidopsis(Arabidopstishalianaa) nd suggest thatthis pathwaycould play a role in the mobilizationof lipids in both pollen and femaletissues
Fertilizationin floweringplants is a multistep process that requires delivery of pollen sperm cells to the ovules, which are located deep within the flower (Johnsonand Preuss,2002).Lipidmetabolismand signaling potentially play important roles in several stages of fertilization,starting with production and releaseof viablepollen (Sanderset al.,2000;Stintziand Browse,2000)and synthesis of the protein-and lipidrich pollen coat, which has a protectivefunctionand provides essential signals for binding, recognition, and hydrationby the stigma (Zinklet al., 1999).Deficienciesin pollen coat lipids lead to hydrationdefects and conditionalmale sterilityin Arabidopsiscermutants (Preusset al., 1993;Fiebig et al, 2000)and pollen coat lipids have been suggested to direct a water gradient,which is requiredfor organizationof cell polarityprior to germination(Wolters-Artset al., 1998)
Summary
COMATOSE(CTS; known as PEROXISOME DEFECTIVE[SPED3]and A. thalianaPEROXISOMAL ABC TRANSPORTER[1AtPXAl]) encodes a peroxisomal ATP-bindingcassette transporter,which was identified in a genetic screen for positive regulators of germination(Russellet al.,2000).cts-1mutantseeds cannotgerminatein theabsenceof classicaldormancybreakingtreatmentsand do not establish in the absence of an exogenous energy source because of theirinabilityto mobilizestoragelipidsby /3-oxidation (Footittet al., 2002,2006).Mutantcts alleles have been identified in screens for seedlings resistant to 2,4-dichlorophenoxybutyricacid and indole butyric acid (IBA;Zolman et al, 2001;Hayashi et al, 2002). ThalianaPEROXISOMAL ABC TRANSPORTER[1AtPXAl]) encodes a peroxisomal ATP-bindingcassette transporter,which was identified in a genetic screen for positive regulators of germination(Russellet al.,2000).cts-1mutantseeds cannotgerminatein theabsenceof classicaldormancybreakingtreatmentsand do not establish in the absence of an exogenous energy source because of theirinabilityto mobilizestoragelipidsby /3-oxidation (Footittet al., 2002,2006).Mutantcts alleles have been identified in screens for seedlings resistant to 2,4-dichlorophenoxybutyricacid and indole butyric acid (IBA;Zolman et al, 2001;Hayashi et al, 2002). PeroxisomalATP-BindingCassetteTransporterand Fertility have implied that y-aminobutyricacid (GABA)and NO aredirectionalsignalsparticipatingin pollen tube guidancein Arabidopsis(Palaniveluet al.,2003;Prado et al, 2004)
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