The Mechanism Of The Arabidopsis EFD Gene Affecting The Formation Of Pollen Wall Pattern

Pollen formation is essential for the reproduction of angiosperms.The normal development of pollen wall plays a key role in producing mature and viable pollen.Pollen wall can be divided into the outer exine and inner intine.The exine can be further divided into outer sexine and inner nexine.The structure of pollen wall varies among different species.The special structure of pollen wall is called pollen wall pattern.The main factors influencing the formation of pollen wall are considered as callose formation,primexine deposition,plasma membrane formation,sporopollen deposition and other factors.It has been reported that many important genes that affect these processes are responsible for pollen wall pattern.For example,CalS5,is required for callose formation.NPU,RPG1,DEX1 and NEF1 affect primexine formation.CYP703A2,MS2,LAP5 and LAP6 are responsible for the synthesis of pollen.TEK,AGP6,AGP11,AGP23,AGP40 are required for nexine formation.The mutantions of these genes result in the defective pollen wall pattern.But the relationship between these factors and the regulatory mechanism of the pollen wall model is still unclear.The latest study reported the Arabidopsis EFD gene encodes a nuclear localized DNA methyltransferase.The lack of EFD leads to male sterility and has a great influence on callose formation,primexine deposition,sporopollenin deposition and nexine formation.In addition,the expression of a large number of important genes in the efd mutant was significantly down-reg?Lated.In this paper,we use the efd mutant as the starting point.The corresponding genes affected each biological process were respectively transformed into the efd mutant.The nexine formation was not restored.The primexine deposition was recovered but not significant,while the sporopollenin deposition was fully recovered.Therefore,sporopollenin synthesis seemed critical for efd mutant.In addition,most genes related to pollen development in efd background showed significant down-regulation,s?ggesting that there might be a transcriptional inhibitor downstream of EFD to repress the expression of genes.We overexpressed the expression factor HBF in the background of the efd mutant,and the HBF overexpression did not show phenotype at 24 oC.However,when HBF was overexpressed at 26 oC,the plants appeared significantly sterile.Interestingly,when the HBF was knocked out in the efd mutant,the fertility was evidently restored to be normal.Therefore,HBF was likely to be a critical transcriptional factor downstream of EFD.