OsTKPR2 is part of a sporopollenin-producing metabolon required for exine formation in rice.

The sporopollenin polymer is a major component of the pollen exine. Fatty acid derivatives synthesized in the tapetum are among the precursors of sporopollenin. Progress has been made to understand sporopollenin metabolism in rice; however, the underlying molecular mechanisms remain elusive. We found that OsTKPR2 and OsTKPR1 share a similar expression pattern, and their coding proteins have a similar subcellular localization and enzyme activities towards reduced tetraketide α-pyrone and hydroxylated tetraketide α-pyrone. Unexpectedly, OsTKPR1pro:OsTKPR2-eGFP could not rescue the phenotype of ostkpr1-4. Three independent ostkpr2 mutant lines generated by CRISPR/Cas9 displayed reduced male fertility to various extents which were correlated with the severity of gene disruptions. Notably, the anther cuticle, Ubisch bodies, and pollen development were affected in the ostkpr2-1 mutant, where a thinner pollen exine was noticed. OsTKPR1 and OsTKPR2 were integrated into a metabolon including OsACOS12 and OsPKS2, which resulted in a significant increased enzymatic efficiency when both OsTKPR1 and OsTKPR2 were present, indicating the mutual dependence of OsTKPR2 and OsTKPR1 for their full biochemical activities. Thus, our results demonstrated that OsTKPR2 is required for anther and pollen development where an OsTKPR2-containing metabolon is functional during rice sporopollenin synthesis. Furthermore, the cooperation and possible functional divergence between OsTKPR2 and OsTKPR1 is also discussed.

Arabidopsis exocyst subunit SEC6 is involved in cell plate formation during Microgametogenesis.

Cytokinesis during pollen mitosis I is critical for cell division and differentiation in the male gametophyte development, but the vesicle trafficking mechanisms in this process are largely unknown. Exocyst is an octameric tethering complex which plays multiple important roles in plant cell vesicle trafficking. Here we report the characterization of exocyst subunit SEC6 in the cytokinesis during pollen mitosis I. We found that significantly amount of pollen from two sec6/+ mutant alleles arrested at the transition from unicelluar stage microspore to bicellular stage. Further analysis showed that sec6 mutation impaired cell plate formation and led to vesicles accumulation in cytoplasm. The localization of KNOLLE on the cell plate was compromised. Consistently, SEC6 gene was expressed start from early pollen development stage and SEC6-GFP localized to the cell plate. These results indicated that SEC6 participated in the cell plate formation during pollen mitosis I, where it might help to tether the vesicles before fusion.

Syntaxin of plants31 (SYP31) and SYP32 is essential for Golgi morphology maintenance and pollen development.

Pollen development is a key process for the sexual reproduction of angiosperms. The Golgi plays a critical role in pollen development via the synthesis and transport of cell wall materials. However, little is known about the molecular mechanisms underlying the maintenance of Golgi integrity in plants. In Arabidopsis thaliana, syntaxin of plants (SYP) 3 family proteins SYP31 and SYP32 are the only two Golgi-localized Qa-soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs) with unknown endogenous functions. Here, we demonstrate the roles of SYP31 and SYP32 in modulating Golgi morphology and pollen development. Two independent lines of syp31/+ syp32/+ double mutants were male gametophytic lethal; the zero transmission rate of syp31 syp32 mutations was restored to largely normal levels by pSYP32:SYP32 but not pSYP32:SYP31 transgenes, indicating their functional differences in pollen development. The initial arrest of syp31 syp32 pollen occurred during the transition from the microspore to the bicellular stage, where cell plate formation in pollen mitosis I (PMI) and deposition of intine were abnormal. In syp31 syp32 pollen, the number and length of Golgi cisterna were significantly reduced, accompanied by many surrounding vesicles, which could be largely attributed to defects in anterograde and retrograde trafficking routes. SYP31 and SYP32 directly interacted with COG3, a subunit of the conserved oligomeric Golgi (COG) complex and were responsible for its Golgi localization, providing an underlying mechanism for SYP31/32 function in intra-Golgi trafficking. We propose that SYP31 and SYP32 play partially redundant roles in pollen development by modulating protein trafficking and Golgi structure.

Arabidopsis COG6 is essential for pollen tube growth and Golgi structure maintenance.

The conserved oligomeric Golgi (COG) complex, which consists of eight subunits named COG1-COG8, is highly conserved with homologous subunits present in most eukaryotic species. In yeast and mammalian, the COG complex has been implicated in the tethering of retrograde intra-Golgi vesicles. Although homologs of COG subunits have been identified in Arabidopsis, the functions of the complex and its subunits remain to be fully elucidated. In this study, we have utilized genetic and cytologic approaches to characterize the role of the COG6 subunit. We showed that a mutation in COG6 caused male transmission defect due to aberrant pollen tube growth. At the subcellular level, Golgi bodies exhibited altered morphology in cog6 pollen and cell wall components were incorrectly deposited in pollen tubes. COG6 fused to green fluorescent protein (GFP), which complemented the aberrant growth of cog6 pollen tubes, was localized to the Golgi apparatus. We propose that COG6, as a subunit of the COG complex, modulates Golgi morphology and vesicle trafficking homeostasis during pollen tube growth.

Overexpressed Tomosyn Binds Syntaxins and Blocks Secretion during Pollen Development.

SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) complex formation is necessary for intracellular membrane fusion and thus has a key role in processes such as secretion. However, little is known about the regulatory factors that bind to Qa-SNAREs, which are also known as syntaxins (SYPs) in plants. Here, we characterized Arabidopsis (Arabidopsis thaliana) Tomosyn protein (AtTMS) and demonstrated that it is a conserved regulator of SYPs in plants. AtTMS binds strongly via its R-SNARE motif-containing C terminus to the Qa domain of PM-resident, pollen-expressed SYP1s (SYP111, SYP124, SYP125, SYP131, and SYP132), which were narrowed down from 12 SYPs. AtTMS is highly expressed in pollen from the bicellular stage onwards, and overexpression of AtTMS under the control of the UBIQUITIN10, MSP1, or LAT52 promoter all resulted in defective pollen after the microspore stage in which secretion was inhibited, leading to the failure of intine deposition and cell plate formation during pollen mitosis I. In tobacco (Nicotiana benthamiana) leaf epidermal cells, overexpression of AtTMS inhibited the secretion of secreted GFP. The defects were rescued by mCherry-tagged SYP124, SYP125, SYP131, or SYP132. In vivo, SYP132 partially rescued the pMSP1:AtTMS phenotype. In addition, AtTMS, lacking a transmembrane domain, was recruited to the plasma membrane by SYP124, SYP125, SYP131, and SYP132 and competed with Vesicle-Associated Membrane Protein721/722 for binding to, for example, SYP132. Together, our results demonstrated that AtTMS might serve as a negative regulator of secretion, whereby active secretion might be fine-tuned during pollen development.

Arabidopsis COG Complex Subunits COG3 and COG8 Modulate Golgi Morphology, Vesicle Trafficking Homeostasis and Are Essential for Pollen Tube Growth.

Spatially and temporally regulated membrane trafficking events incorporate membrane and cell wall materials into the pollen tube apex and are believed to underlie the rapid pollen tube growth. In plants, the molecular mechanisms and physiological functions of intra-Golgi transport and Golgi integrity maintenance remain largely unclear. The conserved oligomeric Golgi (COG) complex has been implicated in tethering of retrograde intra-Golgi vesicles in yeast and mammalian cells. Using genetic and cytologic approaches, we demonstrate that T-DNA insertions in Arabidopsis COG complex subunits, COG3 and COG8, cause an absolute, male-specific transmission defect that can be complemented by expression of COG3 and COG8 from the LAT52 pollen promoter, respectively. No obvious abnormalities in the microgametogenesis of the two mutants are observed, but in vitro and in vivo pollen tube growth are defective. COG3 or COG8 proteins fused to green fluorescent protein (GFP) label the Golgi apparatus. In pollen of both mutants, Golgi bodies exhibit altered morphology. Moreover, γ-COP and EMP12 proteins lose their tight association with the Golgi. These defects lead to the incorrect deposition of cell wall components and proteins during pollen tube growth. COG3 and COG8 interact directly with each other, and a structural model of the Arabidopsis COG complex is proposed. We believe that the COG complex helps to modulate Golgi morphology and vesicle trafficking homeostasis during pollen tube tip growth.

AtVps11 is essential for vacuole biogenesis in embryo and participates in pollen tube growth in Arabidopsis.

Vacuoles are multiple functional and essential organelles in plants. Studies in Saccharomyces cerevisiae had identified a tethering factor HOPS (Homotypic Fusion and Vacuolar Protein Sorting) complex that plays a critical role in vacuole biogenesis. The HOPS complex consists of four core subunits (Vps11, Vps16, Vps18 and Vps33) and two special subunits (Vps39 and Vps41). All these subunits were found in Arabidopsis, and our knowledge of the function of Arabidopsis HOPS complex are still limited. In this study, we investigated the function of AtVps11 gene in Arabidopsis, we found that vps11/- lead to embryo lethal, vacuole biogenesis in embryo was impaired. Furthermore, pollen tube growth was arrested by vps11 mutation, however, no obvious vacuole biogenesis defects were found in vps11 pollen tube. Our study indicated that in Arabidopsis, Vps11 is required for vacuole biogenesis in embryo, which is essential for embryogenesis. It also plays a role in pollen tube growth but looks not required for vacuole biogenesis in pollen tube.

Arabidopsis EXO70A1 recruits Patellin3 to the cell membrane independent of its role as an exocyst subunit.

The exocyst is a well-known complex which tethers vesicles at the cell membrane before fusion. Whether an individual subunit can execute a unique function is largely unknown. Using yeast-two-hybrid (Y2H) analysis, we found that EXO70A1 interacted with the GOLD domain of Patellin3 (PATL3). The direct EXO70A1-PATL3 interaction was supported by in vitro and in vivo experiments. In Arabidopsis, PATL3-GFP colocalized with EXO70A1 predominantly at the cell membrane, and PATL3 localization was insensitive to BFA and TryA23. Remarkably, in the exo70a1 mutant, PATL3 proteins accumulated as punctate structures within the cytosol, which did not colocalize with several endomembrane compartment markers, and was insensitive to BFA. Furthermore, PATL3 localization was not changed in the exo70e2, PRsec6 or exo84b mutants. These data suggested that EXO70A1, but not other exocyst subunits, was responsible for PATL3 localization, which is independent of its role in secretory/recycling vesicle-tethering/fusion. Both EXO70A1 and PATL3 were shown to bind PI4P and PI(4,5)P2 in vitro. Evidence was obtained that the other four members of the PATL family bound to EXO70A1 as well, and shared a similar localization pattern as PATL3. These findings offered new insights into exocyst subunit-specific function, and provided data and tools for further characterization of PATL family proteins.

Serine-arginine protein kinase 1 is associated with hepatocellular carcinoma progression and poor patient survival.

The pre-mRNA splicing regulator serine-arginine protein kinase 1 (SRPK1) promotes cancer development and various pathophysiological processes. However, the clinical relevance of SRPK1 in hepatocellular carcinoma (HCC) is not clear. This study investigates the expression and prognostic value of SRPK1 in HCC. We found that SRPK1 expression was significantly upregulated at the mRNA and protein level in all HCC cell lines or HCC tissue samples compared with the hepatic cell line or matched noncancerous tissue samples, respectively. Higher SRPK1 expression significantly correlated with clinical staging (p = 0.031), survival time (p = 0.004), and gender (p = 0.011) of HCC patients. Together, our study showed that SRPK1 is overexpressed in HCC and may be a promising indicator of prognosis for HCC patients.

Treatment of Corticosteroid-Resistant Vascular Tumors Associated with the Kasabach-Merritt Phenomenon in Infants: An Approach with Transcatheter Arterial Embolization Plus Vincristine Therapy.

PURPOSE: To investigate the effectiveness and application of transcatheter arterial embolization (TAE) plus systemic vincristine for treatment of corticosteroid-resistant vascular tumors associated with Kasabach-Merritt phenomenon in infants. MATERIALS AND METHODS: TAE was performed in 17 infants (average age, 4.3 mo ± 2.4; range, 1-10 mo) with corticosteroid-resistant vascular tumors associated with Kasabach-Merritt phenomenon, followed by intravenous vincristine once weekly for systemic chemotherapy. The effects and complications were observed and evaluated after a cycle (1 cycle: TAE plus treatment with vincristine every 4 weeks). Cycles were repeated in infants with platelet counts < 150 × 10(9)/L. RESULTS: In 17 patients, 36 treatment cycles were successfully performed. The platelet count for all patients increased to ≥ 100 × 10(9)/L for the first time at 6.0 days ± 3.5; the platelet level of 15 infants was maintained at levels > 150 × 10(9)/L at 57.5 days ± 16.5. Before treatment, two infants had a normal fibrinogen level (2.21 g/L and 2.34 g/L); the fibrinogen level in the other 15 infants was first found to be increased to ≥ 2.0 g/L at 7.0 days ± 3.4 and was stabilized at levels > 2.0 g/L at 55.9 days ± 13.8 after treatment. Complications were graded as major in four cases and as minor in 13 cases. CONCLUSIONS: TAE plus vincristine can rapidly improve levels of platelets and fibrinogen, and it is an effective method for treatment of corticosteroid-resistant vascular tumors associated with Kasabach-Merritt phenomenon in infants.

The ARID-HMG DNA-binding protein AtHMGB15 is required for pollen tube growth in Arabidopsis thaliana.

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 AtHMGB15 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 AtHMGB15 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 AtHMGB15 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 AtHMGB15 functions in pollen tube growth through the regulation of gene expression.

Preoperative transcatheter arterial chemoembolization of hepatoblastoma in infants.

PURPOSE: To evaluate the effect of preoperative transcatheter arterial chemoembolization of hepatoblastoma in infants. MATERIALS AND METHODS: Clinical data of 21 infants with hepatoblastoma treated between July 2008 and July 2012 in a single hospital were retrospectively analyzed. After preliminary diagnosis, surgical resection was performed in 9 infants (group I), and transcatheter arterial chemoembolization was performed in 12 infants (group II) before conventional resection. Surgical resection was performed when the tumor bulk appeared sufficiently reduced after transcatheter arterial chemoembolization alone or transcatheter arterial chemoembolization following chemotherapy in cases of pulmonary metastases. RESULTS: Tumor shrinkage ranged from 25%-91% with a mean reduction of 69% (t = 3.816, P = .003) in group II. α-Fetoprotein levels were markedly decreased from 49%-99% with a mean level of 95% (t = 4.871, P = .000) in group II. Specimens in group II showed massive necrosis with a mean percentage of 72% with no significant treatment-related toxicity. In group II, the surgical time was significantly shorter (t = 3.438, P = .003), intraoperative blood loss was considerably less (t = 3.459, P = .003), and the weight of the resected liver was significantly less (t = 3.785, P = .001). Of 21 patients, 16 survived for 50 months without recurrence. CONCLUSIONS: Transcatheter arterial chemoembolization effectively reduced tumor volume, decreased α-fetoprotein, and reduced intraoperative hemorrhage. It represents a safe and effective adjuvant bridge to successful surgery for hepatoblastoma in infants.

Oxidized cellulose microneedle patch combined with vascular embolization and local delivery of timolol maleate for hemangiomas.

Hemangiomas are superficial tumors characterized by dense vascular structures that often affect the patient's aesthetic appearance due to the obvious red appearance on the skin. Current treatments, especially timolol maleate in the form of eye drops and hydrogels, suffer from low transdermal drug delivery rates, resulting in prolonged treatment time. To address this challenge, our study introduced a soluble microneedle patch with dextran as the main material to form microcatheters for sustained delivery of timolol maleate. In addition, we proposed a vascular embolization strategy to disrupt the blood supply in hemangiomas. Oxidized cellulose (C-cellulose) was selected for its excellent hemostatic properties. We incorporated C-cellulose into dextran microneedles to facilitate thrombosis in the vascular-rich areas of hemangiomas. The innovative microneedle patch we developed can penetrate the skin to a depth of 430 µm and dissolve rapidly within 3 minutes, ensuring direct drug delivery to the subcutaneous layer. Notably, the treated skin area regained its original appearance within two hours after treatment. In addition to excellent skin permeability and rapid dissolution, these patches significantly promoted apoptosis and inhibited cell migration in mouse hemangioendothelioma EOMA cells. Our results demonstrate that this approach not only achieves significant tumor inhibition in a mouse hemangioma model, but also represents a more effective, convenient, and non-invasive treatment option. Therefore, dextran/C-cellulose/timolol maleate microneedle patch (MNs/Timolol) has broad clinical application prospects in the treatment of hemangiomas, minimizing the risk of additional damage and improving treatment efficacy.

A rapid and accurate method for evaluating the degradation of pan-Akt in cells by PROTACs using NanoLuc luciferase.

Proteolysis targeting chimera (PROTAC) is a protein degradation technique that has been increasingly used in the development of new drugs in recent years. Akt is a classical serine/threonine kinase, and its role outside of the kinase has gradually gained attention in recent years, making it one of the proteins targeted by PROTACs. Currently, there are many methods used for the evaluation of intracellular protein degradation, but each has its own advantages or disadvantages. This study aimed to investigate the feasibility of evaluating the degradation of pan-Akt proteins in cells by PROTACs (MS21 and MS170) using the NanoLuc luciferase method. After conducting a thorough comparison between this method and the classical western blot assay in various cells, as well as testing the stability of the experiments between multiple batches, we found that NanoLuc luciferase is a highly accurate, stable, low-cost and easy-to-operate method for the evaluation of intracellular pan-Akt degradation by PROTACs with a short cycle time and high cellular expandability. Given the numerous advantages of this method, it is hypothesized that it could be extended to evaluate the degradation of more target proteins of PROTACs. In summary, the NanoLuc luciferase is a suitable method for early protein degradation screening of PROTAC compounds.

An Update on the Key Factors Required for Plant Golgi Structure Maintenance.

Plant Golgi apparatus serves as the central station of the secretory pathway and is the site where protein modification and cell wall matrix polysaccharides synthesis occur. The polarized and stacked cisternal structure is a prerequisite for Golgi function. Our understanding of Golgi structure maintenance and trafficking are largely obtained from mammals and yeast, yet, plant Golgi has many different aspects. In this review, we summarize the key players in Golgi maintenance demonstrated by genetic studies in plants, which function in ER-Golgi, intra-Golgi and post-Golgi transport pathways. Among these, we emphasize on players in intra-Golgi trafficking.

Arabidopsis CSLD1 and CSLD4 are required for cellulose deposition and normal growth of pollen tubes.

The cell wall is important for pollen tube growth, but little is known about the molecular mechanism that controls cell wall deposition in pollen tubes. Here, the functional characterization of the pollen-expressed Arabidopsis cellulose synthase-like D genes CSLD1 and CSLD4 that are required for pollen tube growth is reported. Both CSLD1 and CSLD4 are highly expressed in mature pollen grains and pollen tubes. The CSLD1 and CSLD4 proteins are located in the Golgi apparatus and transported to the plasma membrane of the tip region of growing pollen tubes, where cellulose is actively synthesized. Mutations in CSLD1 and CSLD4 caused a significant reduction in cellulose deposition in the pollen tube wall and a remarkable disorganization of the pollen tube wall layers, which disrupted the genetic transmission of the male gametophyte. In csld1 and csld4 single mutants and in the csld1 csld4 double mutant, all the mutant pollen tubes exhibited similar phenotypes: the pollen tubes grew extremely abnormally both in vitro and in vivo, which indicates that CSLD1 and CSLD4 are not functionally redundant. Taken together, these results suggest that CSLD1 and CSLD4 play important roles in pollen tube growth, probably through participation in cellulose synthesis of the pollen tube wall.

Effect of model choice in genetic association studies: DRD4 exon III VNTR and cigarette use in young adults.

A major concern with the vast literature associating the highly polymorphic 48 bp VNTR in exon III of the human dopamine receptor D4 gene (DRD4) with various behavioral phenotypes is the lack of concordance between studies. Part of the problem arises from the absence of a universally accepted scheme for pooling the large number of low frequency genotypes into appropriate categories. Here, we investigated the effect of different pooling strategies and genetic models on the reported association between DRD4-exIII-VNTR polymorphism and cigarette smoking. Genotyping was performed on a large randomly selected community-based sample of 2,274 individuals aged 20-24 years. Participants were grouped into sub-samples based on their genotypes to test specific genetic models. Multiple regression analyses were used to assess the relationship between DRD4-exIII-VNTR genotype and cigarette smoking measures while controlling for confounders. While smoking status and age at start of smoking were not associated with the genotype, a significantly (P = 0.006) higher rate of cigarette consumption was observed among carriers of the 7-repeat (7r) allele. Thus, 7r carriers were not more likely to be smokers but if they did smoke they consumed significantly more cigarettes per day than 4r carriers. Unlike previous studies this association was observed only when comparing carriers of the 7r with the 4r but not the other repeat alleles. Our study demonstrates the need for caution when grouping functionally different DRD4-exIII-VNTR alleles in association studies. It particularly highlights the requirement for better functional characterization of the DRD4-exIII-VNTR alleles for interpreting results from association studies.

Analysis of angiographic characteristics of kaposiform hemangioendothelioma and investigation of the value of transcatheter arterial embolization therapy.

BACKGROUND: This study aimed to analyze the angiographic characteristics of kaposiform hemangioendothelioma (KHE) and investigate the value of transcatheter arterial embolization (TAE) therapy. METHODS: The clinical data of infants diagnosed with KHE at the department from June 2013 to June 2020 were retrospectively analyzed. Of these, 34 infants received TAE therapy. The efficacy of the treatment was evaluated 4 weeks after the therapy. The angiographic characteristics were analyzed by comparing them with the angiographic characteristics of infantile hemangioma (IH), and the times of TAE therapy and the platelet level after each TAE therapy in infants with KHE were summarized. RESULTS: The present study showed that the capillary blush of KHE was irregular with an obscure boundary and nonuniform distribution. Many fine feeding arteries were present. The diameter of the feeding arteries was disproportionate to the volume of the tumor blush. The normal arteries were usually embedded in the tumor blush. The angiography of common IH in infants also showed tumor blush, but it was usually round with a clear boundary and uniform staining, and was distributed on 1 side of the normal arterial trunk. The infants with KHE received TAE therapy for 2 to 5 times/case, with a total of 104.0 times, with an average of 3.1±0.8/case. Among which, the platelets continued to decline for 9 times after TAE therapy and the platelets increased to ≥100×109/L in 7.8±3.2 days for 95 times after TAE therapy, The average relapse time was 30.0±15.9 days. CONCLUSIONS: The feeding arteries of KHE were numerous and fine and were not easily embolized. The application of TAE may rapidly improve the platelet level, but the long-term effect is poor.

Mutations in the Arabidopsis nuclear-encoded mitochondrial phage-type RNA polymerase gene RPOTm led to defects in pollen tube growth, female gametogenesis and embryogenesis.

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.

GNOM-LIKE 2, encoding an adenosine diphosphate-ribosylation factor-guanine nucleotide exchange factor protein homologous to GNOM and GNL1, is essential for pollen germination in Arabidopsis.

In flowering plants, male gametes are delivered to female gametophytes by pollen tubes. Although it is important for sexual plant reproduction, little is known about the genetic mechanism that controls pollen germination and pollen tube growth. Here we report the identification and characterization of two novel mutants, gnom-like 2-1 (gnl2-1) and gnl2-2 in Arabidopsis thaliana, in which the pollen grains failed to germinate in vitro and in vivo. GNL2 encodes a protein homologous to the adenosine diphosphate-ribosylation factor-guanine nucleotide exchange factors, GNOM and GNL1 that are involved in endosomal recycling and endoplasmic reticulum-Golgi vesicular trafficking. It was prolifically expressed in pollen grains and pollen tubes. The results of the present study suggest that GNL2 plays an important role in pollen germination.