Maize Hybrid Heterosis At Seedling Stage Under LN Conditions And Diversity Analysis Of MIR167 Alleles

Maize is one of the most improtant food and feed crops around the word.The physiological responses and tolerance to low nitrogen stress at maize seedling roots are of vital significance for maize growth and development at whole stage. In this study,8 inbred lines and 28 of their diallele crosses had been used into the analysis of the low nitrogen response and heterosis. The natural varation of MIR167 familes and their target genes were analysed and validated by using the seedling samples from a hydroponic culture. Our objectives were to (1) build evaluation protocols on maize seedlings tolerance to low nitrogen stress, (2) evaluate whether the heterosis effect exsited on low nitrogen tolerance analyze, and (3) analyze the natural variation of MIR167 families and their target genes. The key findings of this study are as follows.(1) The. evaluation protols on low nitrogen tolerance across genotypes had been established and used into following analysis of this study Based on this protocol,8 parental lines along with their diallel crosses had been evaluated. The results showed the biomass, the relative chlorophyll contents (SPAD) were significantly reduced at low nitrogen compared with normal nitrogen condition. However, the root/stem ration, lateral roots, root surface, root volume, lateral roots and anthocyanin contents were significantly increased at low nitrogen condition.(2) We analysed heritability, parent-offspring correlation, general combining ability (GCA), specific combining abiligy (SCA) and the heterosis of 9 different traits under two nitrogen levels. We found that there were distinctly genotypic differences among different genotypes under low nitrogen treatment. The heterosis data suggested that GCA and SCA also show the obvious genotypic difference. Therefore, It suggested that we can improve the low nitrogen tolanence via genetic improvement in maize. Moreover, tips and plangt weight had significant heterosis.GCA had great value to the heterosis of tips, but the GCA and SCA had the same value to plant weight.(3) We analysed nitrogen-sensitive differences of 9 different traits to inbrid line and hybrid under two nitrogen levels.These traits can be used to select materials for tolarence to low nitrogen in maize seedling, such as,root volume, tips, anthocyanin.(4) We assessed allelic variation of MIR167 family by resequencing. We found MIR167c was the most conservative among MIR167 family. MIR167b/e had more variation, while MIR167j had less variation. We analysed the expression pattern and interaction with target gene in 4 different small RNA library,which was built with root and stem under two nitrogen levels. Our results suggest that miR167 exhibited tissue specific patterns and was response to low nitrogen. We analyed the degradome sequencing with 5’-RACE to identify the ture target of miR167 in maize. At last, we proved GRMZM2G035405 and GRMZM2G078274 were target genes of miR167.