Molecular Mechanisms Of Maize Auricle Development

The leaf angle is an important trait of leaf types and a key factor determining the plant type. In our research, we explored the molecular mechanism of the development of auricle in three aspects including morphology, SEM and RNA-seq. The main results are as follows:(1) The size of auricle and leaf angle of five different inbred lines were analyzed statistically through morphology, including expand inbred lines (B73,986) and compact inbred lines (986, Chaol, lg1). The size of auricles of inbred lines is positive correlation with the size of leaf angle. So we can conclude that the size of auricle is an important factor that influences the size of leaf angle.(2) The auricles of different stages of B73 and 986 were observed through scanning electron microscope, and there was no significant difference in early stage and late stage between B73 and 986, but the time that auricle cells of middle stage of 986 entered the stage of cell growth and elongation is earlier than that of auricle cells of middle stage of B73. Cell division span of auricle cells of middle stage of 986 was shorter than that of B73, which was the reason that the size of auricles of B73 was bigger than that of 986.(3) Total RNA of different stage of auricles of B73 and 986 inbred lines was extracted to be used in RNA-seq. The samples consist of auricles of different stages including early stage (dark), middle stage (exposed in sunlight, leaf linked did not expand totally), late stage (exposed in sunlight, leaf linked expanded totally), the samples consists of two repetitions, and the number of actual measured genes of B73 and 986 is 33704 and 33840 respectively. And the number of genes that expressed in three stage of B73 and 986 is 24176 and 24924 respectively.(4) The number of DEGs of each stage between 986 and B73 was analyzed statistically. And the result which was analyzed through heatmap showed that the expression level of auxin pathway, cell division pathway and cell division pathway reduced gradually, the expression level of light reaction pathway, calvin cycle pathway and expansin pathway increased gradually. It demonstrated that during the development of auricles, the level of cell division reduced and cells entered the stage of growth and elongation gradually. And the level of expression of light reaction and calvin cycle in late stage increased which was caused by sunlight.(5) The DEGs of middle stage of B73 and 986 were analyzed through Mapman, and the DEGs were divided into 17 categories by functional classification, the DEGs of cell division pathway consisted of two genes which including CYCD1;1 that control the transformation between G1 and S during cell division. And the level of expression of auxin reduced which leaded to the decrease of CYCD1;1, and the expression level of expansin was higher in 986, it demonstrated that the reason that cells entered the stage of growth and elongation early was the decrease of expression level of CYCD1; 1.(6) We find 12 important genes that influence the development of auricle with comparing the GWAS results of previous research and our data. There are 2 genes that have been reported. These genes consists of genes in BR pathway, auxin pathway, polar growth and structure of leaf.To sum up, we detected a large number of genes which might be involved in regulation of auricle through RNA-seq analysis. Some of the candidate genes were not assigned, although some of them got functional annotation in maize genome database. Analysis on these candidate genes could provide new sight for studying the regulation mechanism of auricles with molecular biology approach.