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The common occurrence of polyploidy or whole genome duplication(WGD)in the evolutionary history of all angiosperms points to it evolutionary significance.Indeed,extensive studies on diverse plant taxa have revealed that WGD is a major source of phenotypic novelty and a driving force in evolution and speciation.Polyploids contains two major types,autopolyploidy(WGD of a single species genome)and allopolyploidy(WGD of two or more genomes from difference species constituting different subgenomes).In the case of allopolyploidy,it is believed that novelty is rooted to subgenome interplay,i.e.,genome-wide,and multi-level homeolog interactions.At the level of gene expression,subgenome interaction often results in extensive and often saltational changes in gene expression,a phenomenon collectively termed transcriptomic shock.However,little is known about the instantaneous effect of WGD on expression partitioning of homeologs in a nascent allopolyploid.In this study,we used a set of reciprocal F1 hybrids and tetraploids constructed from subspecies(japonica and indica)of Asian rice(Oryza sativa L.)as a model to investigate the issue.Specifically,we wished to gain insights into expression partitioning of homeologs among tissues in a developmental context.We assayed expression partitioning of parental homeologs of 30 key genes in the hybrids and tetraploids relative to the in vitro hybrids"(Mix)using Sequenom MassARRAY.We found that tetraploids have 44%of loci showing one homeolog silencing,while the frequency of this event occurred in only 4%of the loci in the hybrids.In addition,we observed that Mix and synthetic tetraploids all have higher frequencies of tissue-specific silencing(TSS)than that of F1,revealing an instantaneous role of WGD on homeolog expression partitioning.Our observations appeared in contrast with previous studies,in which newly formed allopolyploids(S1)showed a lower TSS frequency similar to that in F1 hybrids,and therefore suggesting the impact of WGD on homeolog expression needs longer time to be manifested.We further explored factors that might exert an effect on the expression partitioning of homeologs among tissues.We found that TSS frequency in the tetraploids differed at different growth stages,and that roots have much higher frequency of TSS than leaves,suggesting that development and metabolic traits may influence the expression status of duplicated genes in newly formed plant polyploids.