You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
crystal structures of the chi domains of atchi , atchil , atfap1 , and atfap3 were determined as described in supplementary materials and methods and summarized in supplementary table 8 .
ligands bound to the purified atfap proteins were extracted with ethanol and analyzed by reversed - phase hplc - ms .
the effects of fatty acids ( fas ) on the melting temperature of the atfap proteins were measured using a thermofluor - based assay .
homologs of atchi were identified by iterative psi - blast and profile hidden markov model ( hmm ) .
co - expression patterns of a. thaliana genes encoding fap proteins and genes associated with fa biosynthesis were evaluated with data compiled from 72 microarray experiments using metomgraph ( www.metnetdb.org ) .
homozygous atfap1 - 1 , atfap1 - 3 , atfap2 - 1 and atfap2 - 2 mutant alleles ( supplementary fig 14 and supplementary table 3 ) were generated from salk_130560 , salk_039829 , sail_171_c12 and sail_616_d09 ( arabidopsis biological resource center , abrc ) stocks , respectively .
16 and supplementary table 9 ) were generated from a. thaliana col-0 plants , transformed with agrobacterium tumefasciens strain gv3101 containing vector catma1a44560 ( nottingham arabidopsis stock center , nasc ) .
transgenic a. thaliana lines were generated with atfap1 , 2 , 3 promoters or promoter + ctp /or
fas were extracted from plant tissues using barium hydroxide hydrolysis , modified by methylation and analyzed by gas chromatography 
nonadecanoic acid was used as internal standard and a reference fa mixture was used for calibration and retention time determination ( plantmetabolomics.org ) .
crystal structures of the chi domains of atchi , atchil , atfap1 , and atfap3 were determined as described in supplementary materials and methods and summarized in supplementary table 8 .
ligands bound to the purified atfap proteins were extracted with ethanol and analyzed by reversed - phase hplc - ms .
the effects of fatty acids ( fas ) on the melting temperature of the atfap proteins were measured using a thermofluor - based assay .
homologs of atchi were identified by iterative psi - blast and profile hidden markov model ( hmm ) .
co - expression patterns of a. thaliana genes encoding fap proteins and genes associated with fa biosynthesis were evaluated with data compiled from 72 microarray experiments using metomgraph ( www.metnetdb.org ) .
plants were grown in random block designs at 22c under 16 hr light/8 hr dark .
homozygous atfap1 - 1 , atfap1 - 3 , atfap2 - 1 and atfap2 - 2 mutant alleles ( supplementary fig 14 and supplementary table 3 ) were generated from salk_130560 , salk_039829 , sail_171_c12 and sail_616_d09 ( arabidopsis biological resource center , abrc ) stocks , respectively .
16 and supplementary table 9 ) were generated from a. thaliana col-0 plants , transformed with agrobacterium tumefasciens strain gv3101 containing vector catma1a44560 ( nottingham arabidopsis stock center , nasc ) .
transgenic a. thaliana lines were generated with atfap1 , 2 , 3 promoters or promoter + ctp /or
fas were extracted from plant tissues using barium hydroxide hydrolysis , modified by methylation and analyzed by gas chromatography 
nonadecanoic acid was used as internal standard and a reference fa mixture was used for calibration and retention time determination ( plantmetabolomics.org ) .
specialized metabolic enzymes biosynthesize chemicals of ecological importance , often sharing a pedigree with primary metabolic enzymes1 . 
 however , the lineage of the enzyme chalcone isomerase ( chi ) remained a quandary . 
 in vascular plants , chi - catalyzed conversion of chalcones to chiral ( s)-flavanones is a committed step in the production of plant flavonoids , compounds that contribute to attraction , defense2 , and development3 . 
 chi operates near the diffusion limit with stereospecific control4,5 . while associated primarily with plants , the chi - fold occurs in several other eukaryotic lineages and in some bacteria . here 
 we report crystal structures , ligand - binding properties , and in vivo functional characterization of a non - catalytic chi - fold family from plants . 
 a. thaliana contains five actively transcribed chi - fold genes , three of which additionally encode amino - terminal chloroplast - transit sequences ( ctp ) . 
 these three chi - fold proteins localize to plastids , the site of de novo fatty acid ( fa ) biosynthesis in plant cells . 
 furthermore , their expression profiles correlate with those of core fa biosynthetic enzymes , with maximal expression occurring in seeds and coinciding with increased fa storage in the developing embryo . in vitro , 
 these proteins are fatty acid - binding proteins ( fap ) . fap knockout a. thaliana plants exhibit elevated alpha - linolenic acid levels and marked reproductive defects , including aberrant seed formation . 
 notably , the fap discovery defines the adaptive evolution of a stereospecific and catalytically  
 perfected enzyme6 from a non - enzymatic ancestor over a defined period of plant evolution .