| Heterosis is a complex biological phenomenon and has been widely utilized in agriculture, but the underlying mechanism is still an area to be elucidated. Previous studies revealed that the alteration of gene expression between hybrid and its parental lines may be responsible for the observed heterosis. In this thesis,the relationship of some differentially expressed genes to heterosis in maize and arabidopsis were characterized and the main results as follows:1. Cytokinin oxidase genes (CKOs) catalyze the irreversible degradation of cytokinins and play roles in many aspects of plant growth and development. In maize hybrid Zong3/87-1, ZmCKO1A and ZmCK02A displayed low parent-like and below low parent expression pattern respectively in leaf, and both showed above high parent expression pattern in root. In arabidopsis, the overexpression transgenic lines of ZmCKO1A showed increased lateral root number, reduced plant size and bigger seed size, but the overexpression transgenic lines of ZmCK02A displayed the same phenotype as wide type expect the reduced fertility. And, overexpression of ZmCKO1A can not rescue the lateral root of arabidopsis arf7/19 mutant. Moreover, the maize transgenic lines with decreased expression level of ZmCKOlA and ZmCK02A by RNA interference method showed decreased lateral root number when compared to wide type, and the expression levels of ZmARFl and ZmARF27 that are homologous to ARF7 and ARF19 in arabidopsis were declined in transgenic lines.2. MiR166 displayed additivity expression patten in maize hybrid Zong3/87-1. In order to investigate the relationship between miR166 and lateral root heterosis, miR166 overexpression transgenic hybrid combination and its corresponding wide-type hybrid combination were generated.Moreover, cross 87-1 with Zong3 NILs containing the qLRT5-1 from 87-1 and Zong3 respectively.Comparison of F1-MP between different hybrid combinations was analyzed, the results showed that there was no difference in F1-MP between different hybrid combinations, suggesting there was no significant difference between their heterosis of lateral root number.3. MiR167 was up regulated in maize hybrids. Comparison of F1-MP between MiR167 overexpression transgenic hybrid combinations and their respective wide-type hybrid combinations, the results showed that the F1-MP of transgenic hybrid combinations were significantly reduced than their respective wide-type hybrid combinations, suggesting the lateral root number heterosis were changed in transgenic hybrids. Moreover, the result of exogenous NAA treatment showed that the transgenic hybrid was more sensitive to exogenous NAA treatment than the wide type hybrid Zong3/87-1.4. A series of reciprocal hybrids were generated using arabidopsis Col diploid, C24 diploid and their isogenic autotetraploids as parents, and all hybrids flowered significantly later than their corresponding parents. Expression of FRI and FLC in hybrids and their parents were analyzed, the results showed that FRI and FLC displayed additive and above high-parent expression pattern respectively in hybrids, and FLC showed dosage effect on flowering time. FRI and FLC were silenced in C24 and Col respectively by exploiting the RNA interference method. All transgenic lines flowered significantly earlier than their corresponding wide types, and the F1-MP were significantly decreased in transgenic hybrid combinations,suggesting the decrease of expression levels of FRI and FLC can lead to the decrease of flowering time heterosis.5. Taken together, in maize, ZmCKO1A, ZmCK02A and miR167 that were up regulated in hybrid may be benefit to promote the formation of heterosis, but miR166 that displayed additivity expression pattern in hybrid showed no effect on heterosis. In arabidopsis, the additivity expression of FRI in different ploidy hybrids could lead to the over high-parent expression of FLC, the epistatic interaction between FRI and FLC was the major reason for the formation of flowering time heterosis. |
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