| The transition from vegetative growth to flowering sets is a crucial process during the life cycle of plants, involving a series of dynamic developmental process. Compared with most of plants in Poaceae family, such as wheat(Triticum aestivum) and rice(Oryza sativa), floral transition is more complex in maize(Zea mays), because it produces male and female flower separately. The inflorescence development in maize is determined by three different types of meristems: the spikelet-pair meristems(SPMs), spikelet meristems(SMs) and floral meristems(FMs). As the maize genome sequences have been released and its special flower structure, it has been used as an important and excellent model for the molecular study of the inflorescence development in grasses.Auxin is a class of plant hormones that plays fundamental roles in various biological processes, such as phototropism, gravitropism, organgenesis, and vascular patterning. Until now, four Trp-dependent auxin biosynthesis pathways have been identified. Among them, the trypamine(TAM) pathway is the major IAA biosynthetic pathway, which produces auxin to support normal embryogenesis, flower development, seedling growth, and vascular patterning in plants. YUCCA(YUC) is a flavin monooxygenase-like enzyme that plays a key role in oxidizing TAM to N-hydroxytryptaine, which is a rate-limiting step in auxin biosynthesis. Polar auxin transport also plays important roles in plant organogenesis and differentiation. PIN-formed(PIN) protein family is a type of specific auxin efflux carriers which asymmetrically localized within cells in plant, and their polarity determines the direction of intercellular auxin flow.In this study, a DR5rev::mRFPer maize reporter line was used to examine the auxin-responsive signal in female inflorescence development. The RFP fluorescences localized on the emerging spikelet-pair mristems, spikelet mristems and floral organ mristems, which were associated with the axuin biosynthesis and polar transport. Comprehensive analyses including phylogenetic analysis, gene structure analysis and expression pattern analysis was carried out to determine the characteristics of genes related to auxin biosynthesis(YUC) and transport(PIN), and their functions in maize female inflorescence development. The main results are listed as follows:Using Arabidopsis(Arabidopsis thaliana) YUCs as queries, blast searches were carried out to identify genes encoding YUCs in maize. In total, 14 YUC genes were identified in maize, which is named ZmYUC1-ZmYUC14. Phylogenetic analysis of YUCs in Arabidopsis, rice and maize revealed that maize YUCs are close to rice YUCs rather than that of Arabidopsis. In addition, many clades only contain members of rice and maize YUCs, suggesting that the expansion of YUC family in monocot and dicot experiences different evolutionary histories. Phylogenetic analysis of maize YUCs showed that ZmYUCs in the same group share similar gene structures. ZmYUCs distributed unevenly on seven chromosomes of maize, no members were found to be located on chromosomes 5, 6 and 9. By quantitative real-time PCR(qRT-PCR), the expression patterns of 14 ZmYUC genes were detected in various vegetative and reproductive organs. 12 genes were found to be expressed specificially or preferentially at different stages of female inflorescence development, especially in SPM and SM2 stage. In situ hybridization analysis of ZmYUC3 and ZmYUC4 showed that their transcripts were located in the primordia of female inflorescence. The expression analyses results suggest that ZmYUCs may play important roles in maize female inflorescence development. In addition, we constructed the over-expression vector of ZmYUC4 and the artificial microRNA vector of ZmYUC3, ZmYUC4 and ZmYUC8. Then the two vectors were successfully introduced into immature embryos of maize by Agrobacterium-mediated transformation method to obtain transgenic plants which will be used for genetic and molecular analysis in maize female inflorescence development.Previous studies have identified 14 members of ZmPINs in maize. The expression patterns of these ZmPINs in the female inflorescence development were analyzed by qRTPCR. The results showed 11 ZmPINs were specificially or preferentially expressed in maize female inflorescence at various stages rather than vegetative organs, especially at SPM, SM1, and F stages. The fluorescence signals of pZmPIN1a::ZmPIN1a::YFP transgenic plants were detected predominantly in the developing and newly formed primordia. Also, analysis of DR5rev::mRFPer and pZmPIN1a::ZmPIN1a::YFP transgenic plants revealed that the patterns of auxin distribution and poplar auxin transport were significantly different between axillary buds at different nodes, the upper axillary bud showed stronger auxin-responsive signals and polar auxin transport siganls.Overall, according to the spatial-temporal expression pattern of auxin biosynthetic-related YUC gene family and poplar auxin transport-related PIN gene family, it was found that a large number of genes in the two gene family preferentially expressed in various primordia during maize female inflorescence. Our results suggest that the auxin biosynthesis and auxin poplar transport play important roles in maize female inflorescence development. The data provide important information for elucidating the function of auxin in female inflorescence development of maize. |
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