| Maize is the first major grain crop in China,so increasing maize yield is an important breeding objective to meet the increasing demand.Therefore,mapping and cloning functional genes will provide potential gene resources for molecular design breeding.Two genes,encoding the transcription factor ZmSPL,were previously cloned,and their biological functions were identified by ectopic expression in Arabidopsis.In this research,we further analyzed the relationship between grain weight and ZmSPLl and ZmSPL2 by integrating the forward and reverse genetic strategies.And the biological functions of ZmSPLl and ZmSPL2 were tested to clarify the potential mechanism in maize yield.The main results obtained are as follows:1.Genes expression in grains of ten maize inbred lines,which exhibits great diversifications in grain weight,were tested at 10 and 14 DAP by real-time PCR.The relationship between grain weight and genes expression was analyzed,and we found that the grain weight correlated significantly with the expression of ZmSPLl and ZmSPL1.2 A genetic linkage map consisting of SSR molecular markers was constructed using the F2 population which was derived from 87-1(large grain)x B73(small grain)cross based on gene expression.Following composite interval mapping(CIM),a total of fourteen QTLs were detected,including eight QTLs for kernel length(KL),three QTLs for kernel width(KW)and another three QTLs for hundred kernel weights(HKW),explaining 2.34-8.26%,6.82-13.31%and 4.24-7.26%of the phenotypic variation,respectively.Through comparative genomics,ZmSPL1 and ZmSPL1 were found within the confidence intervals of two HKW QTLs,qHKWl and qHKW4-2,respectively.A highly significant positive correlation between each of the two ZmSPL genes with HKW were observed by single marker analysis using three 87-1/B73 F,populations at different locations(Beijing,Hebei and Jilin).ZmSPL1 and ZmSPL2 seem to be promising candidate genes for grain weight in maize.3.To elucidate the biological functions of the two ZmSPL genes,we ectopically expressed them in rice.The overexpression of these two genes in rice both resulted in longer grains,and significantly increased grain weight,whereas there were no significant in terms of plant height,spike length,grain number per spike,flag leaf length,tiller number and grains starch and protein content between overexpression lines and wild type.Microscopic investigation of the cells,which were in the central point of the lemma in the vertical orientation and were at the inner spikelet hull surface,revealed that enlarged grains were not caused by the cell size but the increased cell number.4.Moreover,overexpression of ZmSPLl in maize contributed to enhanced ear length,ear diameter,grains per row and grain weight.However,seedling traits,plant height and number of days for flowering were not changed in transgenic maize.Microscopic investigation of endosperm cell revealed that cells became larger in transgenic lines than those in the wild type.The analysis of the expression patterns of cell cycle-related genes demonstrated that ZmSPLl might promote the rate of cell division.Compared with the wild type,the protein and starch content in the grains from transgenic maize significantly decreased and increased,respectively.Collectively,our results demonstrate that ZmSPL1 gene contributes to the increased capacity of endosperm and the accumulation of assimilation production through regulating cell size and proliferation,which in turn benefits the increased grain size,weight and starch content. |
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