Structure and Origin of theWhite CapLocus and Its Role in Evolution of Grain Color in Maize.
Selection for yellow- and white-grain types has been central to postdomestication improvement of maize. While genetic control of carotenoid biosynthesis in endosperm is attributed primarily to theYellow1(Y1) phytoene synthase gene, less is known about the role of the dominant white endosperm factorWhite Cap(Wc). We show that theWclocus contains multiple, tandem copies of aCarotenoid cleavage dioxygenase 1(Ccd1) gene that encodes a carotenoid-degrading enzyme. A survey of 111 maize inbreds and landraces, together with 22 teosinte accessions, reveals thatWcis exclusive to maize, where it is prevalent in white-grain (y1) varieties. Moreover,Ccd1copy number varies extensively amongWcalleles (from 1 to 23 copies), and confers a proportional range ofCcd1expression in diverse organs. We propose that this dynamic source of quantitative variation inCcd1expression was created in maize shortly after domestication by a two-step,Tam3Ltransposon-mediated process. First, a chromosome segment containingCcd1and several nearby genes duplicated at a position 1.9 Mb proximal to the progenitorCcd1rlocus on chromosome 9. Second, a subsequent interaction ofTam3Ltransposons at the new locus created a 28-kb tandem duplication, setting up expansion ofCcd1copy number by unequal crossing over. In this way, transposon-mediated variation in copy number at theWclocus generated phenotypic variation that provided a foundation for breeding and selection of white-grain color in maize.
Key Laboratory of Plant Cell Engineering and Germplasm Innovation, Ministry of Education, School of Life Sciences, Shandong University, Jinan, Shandong 250100, China.
Bao-Cai
BC
Tan
Plant Molecular Cellular Biology Program and Genetics Institute, Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611.
Jiahn-Chou
JC
Guan
Key Laboratory of Plant Cell Engineering and Germplasm Innovation, Ministry of Education, School of Life Sciences, Shandong University, Jinan, Shandong 250100, China.
Shuo
S
Ding
Plant Molecular Cellular Biology Program and Genetics Institute, Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611.
Shan
S
Wu
Plant Molecular Cellular Biology Program and Genetics Institute, Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611.
Jonathan W
JW
Saunders
Plant Molecular Cellular Biology Program and Genetics Institute, Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611.
Karen E
KE
Koch
Plant Molecular Cellular Biology Program and Genetics Institute, Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611 drm@ufl.edu.
Donald R
0000-0001-8694-5117
DR
McCarty
D000483:Alleles; D005075:Biological Evolution; D001947:Breeding; D002338:Carotenoids / Q000096:biosynthesis / Q000235:genetics; D002874:Chromosome Mapping; D003116:Color; D056915:DNA Copy Number Variations; D049308:Dioxygenases / Q000096:biosynthesis / Q000235:genetics*; D002523:Edible Grain / Q000235:genetics* / Q000254:growth & development; D018506:Gene Expression Regulation, Plant; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase / Q000235:genetics; D010802:Phylogeny; D010860:Pigments, Biological / Q000096:biosynthesis / Q000235:genetics; D010940:Plant Proteins / Q000096:biosynthesis / Q000235:genetics*; D012641:Selection, Genetic; D003313:Zea mays / Q000235:genetics* / Q000254:growth & development
D010860:Pigments, Biological; D010940:Plant Proteins; C108912:endosperm specific protein, Zea mays; D002338:Carotenoids; D049308:Dioxygenases; C431939:carotenoid cleavage dioxygenase 1; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase
copy number variation; macro-transposition; maize domestication; transposon rearrangement