| Vivipary in plants refers to the phenomenon that sexually produced offspring germinate on the maternal plants with short or no dormancy,the most famous case is the mangrove plants that habitat in tropical or subtropical intertidal zone.Despite some researches had been done in morphological,physiological and ecological level,the molecular mechanism still being mystery.By using Kandelia obovata,a widespread viviparous species in China and of great ecological importance,as material to observed the successive development process from fertilized embryo to mature hypocotyl and determined the key stages and tissues during development.Among them,7 tissues namely fertilized embryo,cotyledon and aixs before and after testa opened,shoot meristem and hypocotyl while still enclosed the pericarp,were sequenced for exploring the gene expression pattern and potential mechanism during transition stages in vivipary.The results show:(1)The development pattern in Kandelia obovata is consistent with the reported viviparous development mode,that is cotyledon grow first then hypocotyl,and cotyledon grow again.Distinct characteristics also be found:early embryo shows green color and in linear shape,the accidented surface of cotyledon facilitate the nutrient absorption from integument,the elongation of hypocotyl instead of endosperm cause the wide open of integument,and cell division in intercalary meristem responsible for the hypocotyl elongation,the terminal of testa and pericarp specialized into parenchyma tissue which make the hypocotyl protrusion easier.(2)120 G clean data were produced from 7 tissues,all these sequences were de novo assembled into 50526 Unigenes.By compared same tissue in different stages and same stage with different tissues,a great number of differential expressed genes(DEGs)represent temporal-spatial difference were acquired.(3)Through Gene Ontology annotation,25452 Unigenes were functionally classified into different categories.Genes related to oxidation reduction,biosynthesis of fatty acid,organ formation,photosynthesis,abscisic acid metabolic,brassinosteroid metabolic,phenoylpropanoid/flovoind/isoprenoid metabolic,nitric oxide metabolic,response to hormone and other enviromental stimulus and so on were enriched while comparing different groups.(4)6687 genes involved in 362 biological pathways were annotated according to KEGG(Kyoto Encyclopedia of Genes and Genomes),these pathways include metabolic pathway,biosynthesis of secondary metabolites,plant hormone signal transduction,photosynthesis,MAPK signaling pathway that strongly related to plant growth and stress resistant.Genes participant in response to hormone,like auxin,cytokinin,gibberellin,abscisic acid and genes encode the key enzymes in the synthesis of carotenoid which is the precursor of ABA exhibit significantly enrichment.Meanwhile,photosystem structure and electronic transport genes also show temporal-spatial difference.Taken together,these pathways may greatly correlate with the vivipary process.(5)799 genes were predicted in 56 transcription factor families,such as bHLH,MYB,bZIP,C2H2,WRKY,NAC,B3,ARF.The enrichment analysis showed that transcription factors express differentially in key stages and tissues.According to their reported function,these transcription factors are putatively regulating the downstream genes involved in specific embryo development and environmental response processes in direct or indirect way.Combined the traditional observation method and modern transcriptome sequencing,the viviparous embryo development processes were studied.We further completed the morphology information of true-vivipary and for the first time obtained the gene expression file during early embryo development.By analyzed the DEGs in different stages and tissues,the molecular mechanism was explored,and a set of vivipary-related genes were screened.Our works provided a solid foundation for future confirmation of these vivipary-related genes and study vivipary in a comprehensive way. |
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