| Pollen tube, part of the male gametophyte of seed plants, is a conduit to transport the sperm cells from the pollen grain to fertilize the egg. The pollen tube extends exclusively at its apex. Extending the cell wall only at the tip minimizes friction between the tube and the invaded tissue. However, the internal machinery and the external interactions that govern the dynamics of pollen tube growth are far from being fully understood. Therefore, the research on the growth of pollen tube is impotant to the further study of the regulation mechanism of plant pollination and fertilization.Pectin is one of the essential component of the primary plant cell wall, it is particularly prominent in pollen tubes, where it control the structure and yielding characteristics of the cell wall at the growing apex of these rapidly expanding cells. Pectin methyl esterase (PME) is a ubiquitous cell-wall-associated enzyme, it plays an important role in cell wall metabolism, because, as noted earlier, the apical tube wall is almost exclusively composed of a pectic network, PME catalyzes the hydrolysis of methylester groups of cell wall pectins into pectate and methanol, thus PME occupies a pivotal position in the control of cell wall growth and development.Triploid loquat has low fertility of pollens, that is, most of the pollen may germination, but the pollen tube can not elongate to the ovary or can not fuse with the female gamete. However, the sterility mechanism of triploid loquat is not clear, so it’s impotant to study the sterility mechanism of triploid loquat.In this study, the homologous sequences of PME gene related the development of pollen tube was choosed based on the transcriptome sequencing of loquat floral bud. And two PME genes were cloned from the loquat floral organ, they are named EjPPMEl and EjPPME2. Subsequently, we analyzed the two cDNA sequence, and obtained characteristics of the proteins from previous studies. The expression pattern of the two genes was analyzed by qRT-PCR during the different stages of floral organ development. To further explore the regulation mechanism of pollen tube and study the sterility mechanism of triploid loquat, We cloned and characterized the PMEs gene. Results of the study were as follows:(1) The full length of EjPPMEl and EjPPME2has been cloned from loquat (Eriobotrya japonica Lindl.) using rapid amplification of the cDNA ends (RACE). The EjPPMEl cDNA has a total length of2201bp with an open reading frame (ORF) and a poly tail. ORF-Find program predicted it coding1737bp in DNA and578amino acid residues. The sequence of EjPPME2is similar to EjPPMEl, but there are differences between two amino acid sites.(2) This study analyzed the target genes’homology, coding protein sequence, and predict the secondary structure and tertiary structure of the protein by the Bioinformatics. The analysis showed that EjPPMEl and EjPPME2proteins mainly contain Alpha helix, Both are hydrophobic transmembrane proteins, and they have two conserved domains, that is PMEI domain and PME domain.(3) The qRT-PCR analysis indicated that transcripts of EjPPMEland EjPPMEl were abundant in the big bud stage of diploid flower, and they expressed only in anther, which suggested the both gene are pollen specific expression gene. Moreover, the qRT-PCR analysis showed that the expression of EjPPMEland EjPPMEl in triploid flower is restrained. The result is constent with the previous finding that the pollen of triploid loquat has low sterility. |
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