Relevance To Heterosis Of Genes Involved In Chromatin Remodeling In Maize

Heterosis is a well-known phenomenon in all kingdoms of life and an importanttool in modern breeding practices of many important crops, for example, maize,sorghum, rice and so on. Heterosis refers to the superior performance of hybridscompared to their homozygous parental inbred lines. The routinely three theoriesemployed to explain this phenomenon are: the dominance theory; the overdominancetheory; and the epistasis theory. In recent studies, epigenetic mechanisms includingDNA methylation, histone modification, siRNA and chromatin remodeling relatedgenes are thought to be involved in the manefestation of heterosis. It remainsunknown how and by what means that epigenetics play a role in heterosis.Maize is the crop in which heterosis has been most extensively utilized forproduction. In this study, we chose17RNAi transgenic lines of the B73geneticbackground obtained from Maize Genetics Stock Center (http://www.aces.uiuc.edu/maize-coop/), whereby genes related to chromatin remodeling were down-regulated by RNAi., We assessed the effect of chromatin remodeling factors on maizeheterosis. The17RNAi transgenic lines were self-pollenated for3times before beingused for generating the F1hybrids. The reciprocal hybrids were obtained by crossingeach of the transgenic lines with Mo17. We surveyed nine agronomic traits intransgenic lines and Mo17as well as their reciprocal F1hybrids, which included earweight (EW), number of rows per ear (NRE), number of kernels per raw (NKR), earlength (EL), length of ear barren tip (LBT), diameter of ear (DE), diameter of cob(DC), cob weight (CW) and one-hundred kernel weight (HKW). Through statisticalanalysis, we aimed to evaluate the possible relationships between expression of thechromatin remodeling-related genes and maize hybrid vigor. Major results obtainedinclude:1. The down-regulation of genes related to chromatin remodeling affected thephenotypes of the RNAi lines. Analysis of the agronomic traits indicated that earcharacters of F1hybrids with down-regulated genes of MBD108, SDG102andVEF101have significant difference compared to their corresponding wild-typecontrols.2. The agronomic traits of some RNAi x Mo17hybrids showed significantchanges compared to their corresponding wild-type controls. And the results alsorevealed a substantial difference between reciprocal hybrids of MBD101、MBD108、 NFD103、SDG102、SRT101and VEF101.3. We found the silencing of most chromatin remodeling related genes (12/17)resulted in changes of heterosis performance according for both middle parentheterosis (MPH) and between better parent heterosis (BPH). Of these genes, threegenes, MBD108, SDG102and VEF101showed the most conspicuous effects.4. Unexpectedly, the expression of some genes related to chromatin remodelingin F1hybrids are not down-regulated in the inbred RNAi lines; instead, they showedtissue/organ-specific silencing in the hybrids, suggesting the expression of these genesmay be more complex in the hybrids.To summarize, our results have indicated that the genes related to chromatinremodeling may have profound impacts on agronomic traits in F1hybrids of maize,and hence manesfestation of heterosis. Thus, we have provided new evidence thatepigenetic regulation plays an important role in heterosis in maize, and by extension,maybe in other crops.