title: Hybrid weakness in a rice interspecific hybrid is nitrogen-dependent, and accompanied by changes in gene expression at both total transcript level and parental allele partitioning.
abstract: BACKGROUND
  Hybrid weakness, a phenomenon opposite to heterosis, refers to inferior growth and development in a hybrid relative to its pure-line parents. Little attention has been paid to the phenomenological or mechanistic aspect of hybrid weakness, probably due to its rare occurrence.
  
  
  RESULTS
  Here, using a set of interspecific triploid F1 hybrids between Oryza sativa, ssp. japonica (genome AA) and a tetraploid wild rice species, O. alta (genome, CCDD), we investigated the phenotypic and physiological differences between the F1 hybrids and their parents under normal and nitrogen-limiting conditions. We quantified the expression levels of 21 key genes involved in three important pathways pertinent to the assayed phenotypic and physiological traits by real-time qRT-PCR. Further, we assayed expression partitioning of parental alleles for eight genes in the F1 hybrids relative to the in silico "hybrids" (parental cDNA mixture) under both normal and N-limiting conditions by using locus-specific cDNA pyrosequencing.
  
  
  CONCLUSIONS
  We report that the F1 hybrids showed weakness in several phenotypic traits at the final seedling-stage compared with their corresponding mid-parent values (MPVs). Nine of the 21 studied genes showed contrasted expression levels between hybrids and parents (MPVs) under normal vs. N-limiting conditions. Interestingly, under N-limiting conditions, the overtly enhanced partitioning of maternal allele expression in the hybrids for eight assayed genes echo their attenuated hybrid weakness in phenotypes, an observation further bolstered by more resemblance of hybrids to the maternal parent under N-limiting conditions compared to normal conditions in a suite of measured physiological traits. Our observations suggest that both overall expression level and differential partitioning of parental alleles of critical genes contribute to condition-specific hybrid weakness.
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun China.
authors.forename: Shuai
authors.identifier: http://orcid.org/0000-0002-1783-8147
authors.initials: S
authors.lastname: Sun
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun China.|Department of Crop and Soil Sciences, Washington State University, Pullman, Washington, United States of America.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Jilin Academy of Agricultural Sciences, Changchun China.
authors.forename: Xiuyun
authors.initials: X
authors.lastname: Lin
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun China.
authors.forename: Jie
authors.initials: J
authors.lastname: Wang
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun China.
authors.forename: Jiamiao
authors.initials: J
authors.lastname: Yu
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun China.|Department of Crop and Soil Sciences, Washington State University, Pullman, Washington, United States of America.
authors.forename: Yue
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun China.
authors.forename: Yiling
authors.initials: Y
authors.lastname: Miao
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun China.
authors.forename: Qiuping
authors.initials: Q
authors.lastname: Li
authors.affiliation: Department of Crop and Soil Sciences, Washington State University, Pullman, Washington, United States of America.
authors.forename: Karen A
authors.initials: KA
authors.lastname: Sanguinet
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun China.
authors.forename: Bao
authors.initials: B
authors.lastname: Liu
mesh_terms: D000483:Alleles; D018506:Gene Expression Regulation, Plant; D056084:Genetic Fitness; D040941:Heredity; D006823:Hybrid Vigor; D006824:Hybridization, Genetic; D009584:Nitrogen / Q000378:metabolism*; D012275:Oryza / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D009584:Nitrogen