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In flowering plants, the interaction of pollen tubes with female tissues is important for the accomplishment of double fertilization. Little information is known about the mechanisms that underlie signalling between pollen tubes and female tissues. In this study, two Arabidopsis pollen tube-expressed CrRLK1L protein kinases, Buddha's Paper Seal 1 (BUPS1) and BUPS2, were identified as being required for normal tip growth of pollen tubes in the pistil. They are expressed prolifically in pollen and pollen tubes and are localized on the plasma membrane of the pollen tube tip region. Mutations in BUPS1 drastically reduced seed set. Most of the bups1 mutant pollen tubes growing in the pistil exhibited a swollen pollen tube tip, leading to failure of fertilization. The bups2 pollen tubes had a slightly abnormal morphology but could still accomplish double fertilization. The bups1 bups2 double mutant exhibited a slightly enhanced phenotype compared to the single bups1 mutants. The BUPS1 proteins could form homomers and heteromers with BUPS2, whereas BUPS2 could only form heteromers with BUPS1. The BUPS proteins could interact with the Arabidopsis pollen-expressed RopGEFs in the yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. The results indicated that the BUPSs may mediate normal polar growth of pollen tubes in the pistil., (© 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd.)

In flowering plants, male gametes are delivered to female gametes for double fertilization through pollen tubes. Therefore, pollen tube growth is crucial for double fertilization. Despite its importance to sexual reproduction, genetic mechanisms of pollen tube growth remain poorly understood. In this study, we characterized the receptor-like cytoplasmic protein kinase (RLCK) gene, MARIS (MRI) that plays critical roles in pollen tube growth. MRI is preferentially expressed in pollen grains, pollen tubes and roots. Mutation in MRI by a Ds insertion led to a burst of pollen tubes after pollen germination. Pollen-rescue assay by pollen and pollen tube-specific expression of MRI in the mri-4 mutant showed that loss of MRI function also severely affected root hair elongation. MRI protein interacted with the protein kinase OXIDATIVE SIGNAL INDUCIBLE1 (OXI1) in the in vitro and in vivo assays, which functions in plant defence and root hair development, and was phosphorylated by OXI1 in vitro. Our results suggest that MRI plays important roles in pollen tube growth and may function in root hair elongation through interaction with OXI1., (© 2016 Institute of Botany, Chinese Academy of Sciences.)

In flowering plants, pollen tube growth is essential for delivery of male gametes into the female gametophyte or embryo sac for double fertilization. Although many genes have been identified as being involved in the process, the molecular mechanisms of pollen tube growth remains poorly understood. In this study, we identified that the Arabidopsis Transmembrane Protein 18 (AtTMEM18) gene played important roles in pollen tube growth. The AtTMEM18 shares a high similarity with the Transmembrane 18 proteins (TMEM18s) that are conserved in most eukaryotes and may play important roles in obesity in humans. Mutation in the AtTMEM18 by a Ds insertion caused abnormal callose deposition in the pollen grains and had a significant impact on pollen germination and pollen tube growth. AtTMEM18 is expressed in pollen grains, pollen tubes, root tips and other vegetative tissues. The pollen-rescued assays showed that the mutation in AtTMEM18 also caused defects in roots, stems, leaves and transmitting tracts. AtTMEM18-GFP was located around the nuclei. Genetic assays demonstrated that the localization of AtTMEM18 around the nuclei in the generative cells of pollen grains was essential for the male fertility. Furthermore, expression of the rice TMEM18-homologous protein (OsTMEM18) driven by LAT52 promoter could recover the fertility of the Arabidopsis attmem18 mutant. These results suggested that the TMEM18 is important for plant growth in Arabidopsis., (© 2015 The Authors. Journal of Integrative Plant Biology published by John Wiley & Sons Australia, Ltd on behalf of Institute of Botany, The Chinese Academy of Sciences.)

Cell wall biosynthesis is indispensable for pollen tube growth. Despite its importance to sexual reproduction, the molecular mechanisms of pollen tube wall biosynthesis remain poorly understood. Here, we report functional characterization of two putative Arabidopsis galacturonosyltransferase genes, GAUT13 and GAUT14, which are essential for pollen tube growth. GAUT13 and GAUT14 encode the proteins that share a high amino acid sequence identity and are located in the Golgi apparatus. The T-DNA insertion mutants, gaut13 and gaut14, did not exhibit any observable defects, but the gaut13 gaut14 double mutants were defective in pollen tube growth; 35.2-37.3% pollen tubes in the heterozygous double mutants were swollen and defective in elongation. The outer layer of the cell wall did not appear distinctly fibrillar in the double mutant pollen tubes. Furthermore, distribution of homogalacturonan labeled with JIM5 and JIM7 in the double mutant pollen tube wall was significantly altered compared to wild-type. Our results suggest that GAUT13 and GAUT14 function redundantly in pollen tube growth, possibly through participation in pectin biosynthesis of the pollen tube wall.

Pollen tube growth and endosperm development are important for fertilization and seed formation. The genetic mechanism of the processes remains poorly understood. This study reports the functional characterization of AtTFIIB1 in pollen tube growth and endosperm development. AtTFIIB1 shares 86% and 44% similarity with AtTFIIB2 and AtTFIIB3/AtpBRP2, respectively. It is expressed in many tissues including vegetative nuclei and generative cells of pollen grains and pollen tubes, endosperm, and embryos. It is thus different from AtTFIIB2, whose expression is not found in the endosperm and vegetative nucleus of mature pollen, and AtTFIIB3/AtpBRP2, which is expressed mostly in male gametophytes and weakly in seeds. Mutations in AtTFIIB1 caused a drastic retardation of pollen tube growth and endosperm development, as well as impaired pollen tube guidance and reception, leading to disruption of fertilization and seed development. Expression of AtTFIIB2 driven by the AtTFIIB1 promoter could restore the defective pollen tube growth, guidance, and reception completely, but only partially recovered the seed development in attfiib1, whilst expression of AtTFIIB3/AtpBRP2 driven by the AtTFIIB1 promoter could rescue only the defective attfiib1 seeds. All these results suggest that AtTFIIB1 plays important roles in pollen tube growth, guidance, and reception as well as endosperm development and is partially functionally different from AtTFIIB2 and AtTFIIB3/AtpBRP2.

In flowering plants, the growth of pollen tubes is essential for the delivery of sperm to the egg cells. Although many factors (including cell-wall properties) are involved in this process, little is known about the underlying molecular mechanisms that regulate the growth of pollen tubes. We report here the characterization of an Arabidopsis mutant male gametophyte defective 4 (mgp4) that is severely defective in pollen tube growth. The mgp4 mutation also impairs root growth of pollen-rescued mgp4 mutant plants generated by expressing MGP4 cDNA under the control of a pollen grain/tube-specific promoter. The MGP4 gene encodes a putative xylosyltransferase and is expressed in many organs/tissues, including pollen tubes and roots. MGP4 protein expressed in Pichia pastoris exhibited xylosyltransferase activity and transferred d-xylose onto l-fucose. The pectic polysaccharide rhamnogalacturonan II (RG-II), isolated from 7-day-old pollen-rescued mutant seedlings, exhibited a 30% reduction in 2-O-methyl d-xylose residues. Furthermore, an exogenous supply of boric acid enhanced RG-II dimer formation and partially restored the root growth of the pollen-rescued mutant seedlings. Taken together, these results suggest that MGP4 plays important roles in pollen tube and root growth by acting as a xylosyltransferase involved in the biosynthesis of pectic RG-II., (© 2011 The Authors. The Plant Journal © 2011 Blackwell Publishing Ltd.)

The mitochondrial genes in Arabidopsis thaliana are transcribed by a small family of nuclear-encoded T3/T7 phage-type RNA polymerases (RPOTs). At least two nuclear-encoded RPOTs (RPOTm and RPOTmp) are located in mitochondria in A. thaliana. Their genetic roles are largely unknown. Here we report the characterization of novel mutations in the A. thaliana RPOTm gene. The mutations did not affect pollen formation, but significantly retarded the growth of the rpoTm mutant pollen tubes and had an impact on the fusion of the polar nuclei in the rpoTm mutant embryo sacs. Moreover, development of the rpoTm/- mutant embryo was arrested at the globular stage. The rpoTm rpoTmp double mutation could enhance the rpoTm mutant phenotype. Expression of RPOTmp under control of the RPOTm promoter could not complement the phenotype of the rpoTm mutations. All these data indicate that RPOTm is important for normal pollen tube growth, female gametogenesis and embryo development, and has distinct genetic and molecular roles in plant development, which cannot be replaced by RPOTmp.

In most flowering plant species, pollination and fertilization occur during the hot summer, so plants must have evolved a mechanism that ensures normal growth of their pollen tubes at high temperatures. Despite its importance to plant reproduction, little is known about the molecular basis of thermotolerance in pollen tubes. Here we report the identification and characterization of a novel Arabidopsis gene, Thermosensitive Male Sterile 1 (TMS1), which plays an important role in thermotolerance of pollen tubes. TMS1 encodes a Hsp40-homologous protein with a DnaJ domain and an a_ERdj5_C domain found in protein disulfide isomerases (PDI). Purified TMS1 expressed in Escherichia coli (BL21 DE3) had the reductive activity of PDI. TMS1 was expressed in pollen grains, pollen tubes and other vegetative tissues, including leaves, stems and roots. Heat shock treatment at 37 degrees C increased its expression levels in growing pollen tubes as well as in vegetative tissues. A knockout mutation in TMS1 grown at 30 degrees C had greatly retarded pollen tube growth in the transmitting tract, resulting in a significant reduction in male fertility. Our study suggests that TMS1 is required for thermotolerance of pollen tubes in Arabidopsis, possibly by functioning as a co-molecular chaperone.

SUMMARY: Pollen formation and pollen tube growth are essential for the delivery of male gametes into the female embryo sac for double fertilization. Little is known about the mechanisms that regulate the late developmental process of pollen formation and pollen germination. In this study, we characterized a group of Arabidopsis AGC kinase proteins, NDR2/4/5, involved in pollen development and pollen germination. The NDR2/4/5 genes are mainly expressed in pollen grains at the late developmental stages and in pollen tubes. They function redundantly in pollen formation and pollen germination. At the tricellular stages, the ndr2 ndr4 ndr5 mutant pollen grains exhibit an abnormal accumulation of callose, precocious germination and burst in anthers, leading to a drastic reduction in fertilization and a reduced seed set. NDR2/4/5 proteins can interact with another group of proteins (MOB1A/1B) homologous to the MOB proteins from the Hippo signaling pathway in yeast and animals. The Arabidopsis mob1a mob1b mutant pollen grains also have a phenotype similar to that of ndr2 ndr4 ndr5 pollen grains. These results provide new evidence demonstrating that the Hippo signaling components are conserved in plants and play important roles in sexual plant reproduction. Significance Statement: The AGC protein kinases NDR2/4/5 play important roles in the late development of pollen grains and the control of pollen germination through interaction with the MOB1A/1B proteins in Arabidopsis. This study suggests that the core components in the Hippo pathway, NDRs and MOBs, are also functionally conserved in plants. [ABSTRACT FROM AUTHOR]

In flowering plants, male gametes (sperm cells) develop within male gametophytes (pollen grains) and are delivered to female gametes for double fertilization by pollen tubes. Therefore, pollen tube growth is crucial for reproduction. The mechanisms that control pollen tube growth remain poorly understood. In this study, we demonstrated that the ARID- HMG DNA-binding protein At HMGB15 plays an important role in pollen tube growth. This protein is preferentially expressed in pollen grains and pollen tubes and is localized in the vegetative nuclei of the tricellular pollen grains and pollen tubes. Knocking down At HMGB15 expression via a Ds insertion caused retarded pollen tube growth, leading to a significant reduction in the seed set. The athmgb15-1 mutation affected the expression of 1686 genes in mature pollen, including those involved in cell wall formation and modification, cell signaling and cellular transport during pollen tube growth. In addition, it was observed that At HMGB15 binds to DNA in vitro and interacts with the transcription factors AGL66 and AGL104, which are required for pollen maturation and pollen tube growth. These results suggest that At HMGB15 functions in pollen tube growth through the regulation of gene expression. [ABSTRACT FROM AUTHOR]

Pollen tube reception involves a pollen tube-synergid interaction that controls the discharge of sperm cells into the embryo sac during plant fertilization. Despite its importance in the sexual reproduction of plants, little is known about the role of gene regulation in this process. We report here that the pollen-expressed transcription factors MYB97, MYB101 and MYB120 probably control genes whose encoded proteins play important roles in Arabidopsis thaliana pollen tube reception. They share a high amino acid sequence identity and are expressed mainly in mature pollen grains and pollen tubes. None of the single or double mutants of these three genes exhibited any visible defective phenotype. Although the myb97 myb101 myb120 triple mutant was not defective in pollen development, pollen germination, pollen tube growth or tube guidance, the pollen tubes of the triple mutants exhibited uncontrolled growth and failed to discharge their sperm cells after entering the embryo sac. In addition, the myb97 myb101 myb120 triple mutation significantly affected the expression of a group of pollen-expressed genes in mature pollen grains. All these results indicate that MYB97, MYB101 and MYB120 participate in pollen tube reception, possibly by controlling the expression of downstream genes. [ABSTRACT FROM AUTHOR]