title: A non-synonymous SNP within the isopentenyl transferase 2 locus is associated with kernel weight in Chinese maize inbreds (Zea mays L.).
abstract: BACKGROUND
  Kernel weight, controlled by quantitative trait loci (QTL), is an important component of grain yield in maize. Cytokinins (CKs) participate in determining grain morphology and final grain yield in crops. ZmIPT2, which is expressed mainly in the basal transfer cell layer, endosperm, and embryo during maize kernel development, encodes an isopentenyl transferase (IPT) that is involved in CK biosynthesis.
  
  
  RESULTS
  The coding region of ZmIPT2 was sequenced across a panel of 175 maize inbred lines that are currently used in Chinese maize breeding programs. Only 16 single nucleotide polymorphisms (SNPs) and seven haplotypes were detected among these inbred lines. Nucleotide diversity (π) within the ZmIPT2 window and coding region were 0.347 and 0.0047, respectively, and they were significantly lower than the mean nucleotide diversity value of 0.372 for maize Chromosome 2 (P < 0.01). Association mapping revealed that a single nucleotide change from cytosine (C) to thymine (T) in the ZmIPT2 coding region, which converted a proline residue into a serine residue, was significantly associated with hundred kernel weight (HKW) in three environments (P <0.05), and explained 4.76% of the total phenotypic variation. In vitro characterization suggests that the dimethylallyl diphospate (DMAPP) IPT activity of ZmIPT2-T is higher than that of ZmIPT2-C, as the amounts of adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP) consumed by ZmIPT2-T were 5.48-, 2.70-, and 1.87-fold, respectively, greater than those consumed by ZmIPT2-C. The effects of artificial selection on the ZmIPT2 coding region were evaluated using Tajima's D tests across six subgroups of Chinese maize germplasm, with the most frequent favorable allele identified in subgroup PB (Partner B).
  
  
  CONCLUSIONS
  These results showed that ZmIPT2, which is associated with kernel weight, was subjected to artificial selection during the maize breeding process. ZmIPT2-T had higher IPT activity than ZmIPT2-C, and this favorable allele for kernel weight could be used in molecular marker-assisted selection for improvement of grain yield components in Chinese maize breeding programs.
authors.affiliation: Institute of Crop Science, Chinese Academy of Agricultural Sciences, National Key Facility for Crop Gene Resources and Genetic Improvement, Beijing 100081, China.
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Weng
authors.forename: Bo
authors.initials: B
authors.lastname: Li
authors.forename: Changlin
authors.initials: C
authors.lastname: Liu
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Yang
authors.forename: Hongwei
authors.initials: H
authors.lastname: Wang
authors.forename: Zhuanfang
authors.initials: Z
authors.lastname: Hao
authors.forename: Mingshun
authors.initials: M
authors.lastname: Li
authors.forename: Degui
authors.initials: D
authors.lastname: Zhang
authors.forename: Xiaoke
authors.initials: X
authors.lastname: Ci
authors.forename: Xinhai
authors.initials: X
authors.lastname: Li
authors.forename: Shihuang
authors.initials: S
authors.lastname: Zhang
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D002681:China; D014644:Genetic Variation; D007178:Inbreeding; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D012639:Seeds / Q000201:enzymology / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development / Q000502:physiology
chemical_list: D010940:Plant Proteins; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase