Overexpression of PwTUA1, a pollen-specific tubulin gene, increases pollen tube elongation by altering the distribution of alpha-tubulin and promoting vesicle transport

BUZZ: an essential gene for postinitiation root hair growth and a mediator of root architecture in Brachypodium distachyon

Here, we discover a player in root development. Recovered from a forward-genetic screen in Brachypodium distachyon, the buzz mutant initiates root hairs but they fail to elongate. In addition, buzz roots grow twice as fast as wild-type roots. Also, lateral roots show increased sensitivity to nitrate, whereas primary roots are less sensitive to nitrate. Using whole-genome resequencing, we identified the causal single nucleotide polymorphism as occurring in a conserved but previously uncharacterized cyclin-dependent kinase (CDK)-like gene. The buzz mutant phenotypes are rescued by the wild-type B. distachyon BUZZ coding sequence and by an apparent homolog in Arabidopsis thaliana. Moreover, T-DNA mutants in A. thaliana BUZZ have shorter root hairs. BUZZ mRNA localizes to epidermal cells and develops root hairs and, in the latter, partially colocalizes with the NRT1.1A nitrate transporter. Based on qPCR and RNA-Seq, buzz overexpresses ROOT HAIRLESS LIKE SIX-1 and -2 and misregulates genes related to hormone signaling, RNA processing, cytoskeletal, and cell wall organization, and to the assimilation of nitrate. Overall, these data demonstrate that BUZZ is required for tip growth after root hair initiation and root architectural responses to nitrate.

Integrated transcriptomic and proteomic analysis of a cytoplasmic male sterility line and associated maintainer line in soybean

INTRODUCTION

Heterosis is a critical phenomenon in crop improvement. Cytoplasmic male sterility (CMS) and Restorer gene (Rf) systems are essential components for heterosis-based breeding. However, the molecular mechanism underlying CMS remains largely unclear in soybean.

METHODS

We integrated a morphological investigation with comparative analyses of transcriptomic and proteomic changes in pollen from the CMS line W931A and its maintainer line, W931B, at the uninucleate microspore (UM) and binucleate pollen (BP) stages.

RESULTS

Compared to W931B, which had healthy, oval pollen grains, W931A showed shrunken or degraded pollen grains with an irregularly thickened endothelium and decreased starch accumulation. Transcriptomic comparisons revealed a total of 865 differentially expressed genes (DEGs) in W931A over the two stages. These genes were primarily associated with pentose and glucuronate interconversions, sphingolipid metabolism, and glycerolipid metabolism. Proteomic analysis revealed 343 differentially expressed proteins (DEPs), which were mainly involved in carbon metabolism, glycolysis/gluconeogenesis, and nitrogen metabolism. Consistently, Gene Ontology (GO) biological process terms related to pollen development were enriched among DEGs at the UM and BP stages. Notably, four genes with demonstrated roles in pollen development were differentially expressed, including AGAMOUS-LIKE 104, PROTEIN-TYROSINE-PHOSPHATASE 1, and PHOSPHOLIPASE A2. A total of 53 genes and the corresponding proteins were differentially expressed in W931A at both the UM and BP stages, and many of these were pectinesterases, polygalacturonases, peroxidases, and ATPases.

DISCUSSION

The results of this study suggest that pollen development in W931A is likely regulated through suppression of the identified DEGs and DEPs. These findings increase our understanding of the molecular mechanism underlying CMS in soybean, aiding future research into soybean fertility and promoting the efficient use of heterosis for soybean improvement.

OsFH3 Encodes a Type II Formin Required for Rice Morphogenesis

The actin cytoskeleton is crucial for plant morphogenesis, and organization of actin filaments (AF) is dynamically regulated by actin-binding proteins. However, the roles of actin-binding proteins, particularly type II formins, in this process remain poorly understood in plants. Here, we report that a type II formin in rice, Oryza sativa formin homolog 3 (OsFH3), acts as a major player to modulate AF dynamics and contributes to rice morphogenesis. osfh3 mutants were semi-dwarf with reduced size of seeds and unchanged responses to light or gravity compared with mutants of osfh5, another type II formin in rice. osfh3 osfh5 mutants were dwarf with more severe developmental defectiveness. Recombinant OsFH3 could nucleate actin, promote AF bundling, and cap the barbed end of AF to prevent elongation and depolymerization, but in the absence of profilin, OsFH3 could inhibit AF elongation. Different from other reported type II formins, OsFH3 could bind, but not bundle, microtubules directly. Furthermore, its N-terminal phosphatase and tensin homolog domain played a key role in modulating OsFH3 localization at intersections of AF and punctate structures of microtubules, which differed from other reported plant formins. Our results, thus, provide insights into the biological function of type II formins in modulating plant morphology by acting on AF dynamics.

Quantitative proteomics reveals dual effects of calcium on radicle protrusion in soybean

To reveal calcium-mediated germination in soybean, a gel-free/label-free proteomics was performed in radicle of seed imbibed with CaCl2. Morphological analysis presented promoting and suppressing performance of seed growth under 5 and 50 mM CaCl2, respectively. A total of 106 and 581 proteins were identified in response to 5 and 50 mM CaCl2, respectively. Among 33 proteins, which were simultaneously affected by 5 and 50 mM CaCl2 imbibition, proteins related to protein metabolism, cell, development, and stress showed reversed abundance in response to CaCl2 on dose-dependent manner. Notably, protein abundance of late embryogenesis abundant (LEA) 4-5, LEA4, and dehydrin decreased and increased by 5 and 50 mM CaCl2, respectively, consistent with the transcript level. Moreover, inhibited biosynthesis of gibberellic acid repressed growth of 5 mM CaCl2-imbibed soybean, while inhibition of abscisic acid biosynthesis released the suppressing effects of 50 mM CaCl2. Taken together, these results suggest that decreased or increased protein abundance of LEA4-5, LEA4, and dehydrin might determine promoting or suppressing effects of low or high level of calcium on soybean through enhancing seed sensitivity to gibberellic acid or abscisic acid during radicle protrusion. SIGNIFICANCE: Calcium serves as a versatile signal in plant growth; however, calcium-mediated germination on dose-dependent manner remains elusive. In this study, dual effects of calcium on radicle protrusion in soybean were investigated using proteomic approach. Radicle growth of germinating seed was improved by 5 mM CaCl2; however, it was retarded by 50 mM CaCl2. Late embryogenesis abundant (LEA) 4-5, LEA4, and dehydrin displayed converse profiles in response to low and high concentrations of CaCl2 at both protein abundance and gene expression level. Inhibited biosynthesis of gibberellic acid (GA) significantly impeded radicle protrusion in presence of low concentration of CaCl2, while inhibiting of abscisic acid (ABA) biosynthesis released suppression induced by high concentration of CaCl2. These findings suggest that LEA proteins are associated with calcium-mediated radicle protrusion on dose-dependent manner, and seed sensitivity to GA and ABA might determine promoting and suppressing effects of calcium on radicle protrusion in soybean.

Overexpression of Two CCCH-type Zinc-Finger Protein Genes Leads to Pollen Abortion in Brassica campestris ssp. chinensis

The pollen grains produced by flowering plants are vital for sexual reproduction. Previous studies have shown that two CCCH-type zinc-finger protein genes in Brassica campestris, BcMF30a and BcMF30c, are involved in pollen development. Due to their possible functional redundancy, gain-of-function analysis is helpful to reveal their respective biological functions. Here, we found that the phenotypes of BcMF30a and BcMF30c overexpression transgenic plants driven by their native promoters were similar, suggesting their functional redundancy. The results showed that the vegetative growth was not affected in both transgenic plants, but male fertility was reduced. Further analysis found that the abortion of transgenic pollen was caused by the degradation of pollen contents from the late uninucleate microspore stage. Subcellular localization analysis demonstrated that BcMF30a and BcMF30c could localize in cytoplasmic foci. Combined with the studies of other CCCH-type genes, we speculated that the overexpression of these genes can induce the continuous assembly of abnormal cytoplasmic foci, thus resulting in defective plant growth and development, which, in this study, led to pollen abortion. Both the overexpression and knockout of BcMF30a and BcMF30c lead to abnormal pollen development, indicating that the appropriate expression levels of these two genes are critical for the maintenance of normal pollen development.

Evolutionary characterization and transcript profiling of β-tubulin genes in flax (Linum usitatissimum L.) during plant development

BACKGROUND

Microtubules, polymerized from alpha and beta-tubulin monomers, play a fundamental role in plant morphogenesis, determining the cell division plane, the direction of cell expansion and the deposition of cell wall material. During polarized pollen tube elongation, microtubules serve as tracks for vesicular transport and deposition of proteins/lipids at the tip membrane. Such functions are controlled by cortical microtubule arrays. Aim of this study was to first characterize the flax β-tubulin family by sequence and phylogenetic analysis and to investigate differential expression of β-tubulin genes possibly related to fibre elongation and to flower development.

RESULTS

We report the cloning and characterization of the complete flax β-tubulin gene family: exon-intron organization, duplicated gene comparison, phylogenetic analysis and expression pattern during stem and hypocotyl elongation and during flower development. Sequence analysis of the fourteen expressed β-tubulin genes revealed that the recent whole genome duplication of the flax genome was followed by massive retention of duplicated tubulin genes. Expression analysis showed that β-tubulin mRNA profiles gradually changed along with phloem fibre development in both the stem and hypocotyl. In flowers, changes in relative tubulin transcript levels took place at anthesis in anthers, but not in carpels.

CONCLUSIONS

Phylogenetic analysis supports the origin of extant plant β-tubulin genes from four ancestral genes pre-dating angiosperm separation. Expression analysis suggests that particular tubulin subpopulations are more suitable to sustain different microtubule functions such as cell elongation, cell wall thickening or pollen tube growth. Tubulin genes possibly related to different microtubule functions were identified as candidate for more detailed studies.

Ectopic expression of CSD1 and CSD2 targeting genes of miR398 in grapevine is associated with oxidative stress tolerance

MicroRNAs (miRNAs) are endogenous small RNAs of -21 nucleotides that play an important role in diverse plant physiological processes at the post-transcriptional level by directing mRNA cleavage or translational inhibition. Previous studies have indicated that down-regulation of miR398 in response to oxidative stress allows up-regulation of the two target genes, cytosolic CSD1 and chloroplastic CSD2 (copper/zinc superoxide dismutase), resulting in protecting the plants to tolerate oxidative stress. In this study, we provide evidence that grapevine miR398 (Vv-miR398), by regulating the expression of its target genes, VvCSD1 and VvCSD2, mediates responses of grapevine to copper (Cu) stress which have been magnified due to increase in Cu-containing pesticide application. The expression of Vv-miR398 was inhibited by different concentrations of Cu stress; on the other hand, there was a steady increase in the activity of VvCSD1 and VvCSD2 genes. The function of VvCSD1 and VvCSD2 under Cu stress was thoroughly examined by overexpressing the use of the VvCSD1 and VvCSD2 in transgenic tobacco (Nicotiana tabacum). We found that both the overexpressed transgenic lines had lower Cu sensitivity and higher Cu tolerance compared with the wild type. In addition, lower levels of ROS and higher levels of SOD activities were accumulated in the transgenic lines in comparison with the wild type under the higher Cu conditions. Furthermore, these transgenic tobacco lines also recorded a higher UV and salt tolerance than the WT plants. These results suggested that overexpressing the VvCSDs will enhance the ROS-scavenging systems and protect the plant against more oxidative damage. Also, more investigations in this line are needed that would provide significant improvements in our understanding the resistance of fruit crops to environmental stress.

OsFH15, a class I formin, interacts with microfilaments and microtubules to regulate grain size via affecting cell expansion in rice

Grain size is an important agronomic trait determining rice yield and is mainly restricted by spikelet hull size. However, it remains largely unknown how the spikelet hull size is regulated. In this study, OsFH15, a class I formin protein in Oryza sativa, was found to be able to regulate the size of cells and spikelet hull. OsFH15-Cas9 and OsFH15-RNAi mutants had decreased grain size with reduced cell length, cell width and cell area of inner epidermal cells of the lemma compared with wild-type plants. By contrast, OsFH15-overexpressed plants had increased grain size with larger cells, as well as more abundant microtubules (MTs) and actin filaments (AFs) arrays. OsFH15 was mainly expressed in shoot apical meristem (SAM), spikelets, spikelet hulls and seeds in rice. In vitro biochemical experiments showed that OsFH15 can efficiently nucleate actin polymerization with or without profilin, can cap the barbed end of AFs, and can bind and bundle both AFs and MTs. OsFH15 can also crosslink AFs with MTs, and preferentially bind MTs to AFs. These results demonstrated that OsFH15 played an important role in grain-size control by affecting cell expansion through regulating AFs and MTs.

Genome-Wide Identification and Analysis of the Type-B Authentic Response Regulator Gene Family in Peach (Prunus persica)

The type-B authentic response regulator (ARR-B) family members serve as DNA-binding transcriptional regulators, whose activities are probably regulated by phosphorylation/dephosphorylation, resulting in the rapid induction of type-A ARR genes. Type-B ARRs are believed to be involved in many biological processes, including cytokinin signaling, plant growth, and stress responses through a chaperone or by isomerization of proline residues during protein folding. The public availability of complete peach genome sequences allows the identification of 23 ARR-B genes by HMMER and blast analysis. Scaffold locations of these genes in the peach genome were determined, and the protein domain and motif organization of peach type-B ARRs were analyzed. The phylogenetic relationships between peach type-B ARRs were also assessed. The expression profiles of peach ARR-B genes revealed that most of the type-B ARRs showed high expression levels in tissues undergoing rapid cell division and may engage more cytokinins, like half-opened flowers, fruits at expansion stages, and young leaves. These findings not only contribute to a better understanding of the complex regulation of the peach ARR-B gene family, but also provide valuable information for future research in peach functional genomics.

Importance of organellar proteins, protein translocation and vesicle transport routes for pollen development and function

Protein translocation. Cellular homeostasis strongly depends on proper distribution of proteins within cells and insertion of membrane proteins into the destined membranes. The latter is mediated by organellar protein translocation and the complex vesicle transport system. Considering the importance of protein transport machineries in general it is foreseen that these processes are essential for pollen function and development. However, the information available in this context is very scarce because of the current focus on deciphering the fundamental principles of protein transport at the molecular level. Here we review the significance of protein transport machineries for pollen development on the basis of pollen-specific organellar proteins as well as of genetic studies utilizing mutants of known organellar proteins. In many cases these mutants exhibit morphological alterations highlighting the requirement of efficient protein transport and translocation in pollen. Furthermore, expression patterns of genes coding for translocon subunits and vesicle transport factors in Arabidopsis thaliana are summarized. We conclude that with the exception of the translocation systems in plastids-the composition and significance of the individual transport systems are equally important in pollen as in other cell types. Apparently for plastids only a minimal translocon, composed of only few subunits, exists in the envelope membranes during maturation of pollen. However, only one of the various transport systems known from thylakoids seems to be required for the function of the "simple thylakoid system" existing in pollen plastids. In turn, the vesicle transport system is as complex as seen for other cell types as it is essential, e.g., for pollen tube formation.

Arabidopsis FIM5 decorates apical actin filaments and regulates their organization in the pollen tube

The actin cytoskeleton is increasingly recognized as a major regulator of pollen tube growth. Actin filaments have distinct distribution patterns and dynamic properties within different regions of the pollen tube. Apical actin filaments are highly dynamic and crucial for pollen tube growth. However, how apical actin filaments are generated and properly constructed remains an open question. Here we showed that Arabidopsis fimbrin5 (FIM5) decorates filamentous structures throughout the entire tube but is apically concentrated. Apical actin structures are disorganized to different degrees in the pollen tubes of fim5 loss-of-function mutants. Further observations suggest that apical actin structures are not constructed properly because apical actin filaments cannot be maintained at the cortex of fim5 pollen tubes. Actin filaments appeared to be more curved in fim5 pollen tubes and this was confirmed by measurements showing that the convolutedness and the rate of change of convolutedness of actin filaments was significantly increased in fim5 pollen tubes. This suggests that the rigidity of the actin filaments may be compromised in fim5 pollen tubes. Further, the apical cell wall composition is altered, implying that tip-directed vesicle trafficking events are impaired in fim5 pollen tubes. Thus, we found that FIM5 decorates apical actin filaments and regulates their organization in order to drive polarized pollen tube growth.

Profilin Regulates Apical Actin Polymerization to Control Polarized Pollen Tube Growth

Pollen tube growth is an essential step during flowering plant reproduction, whose growth depends on a population of dynamic apical actin filaments. Apical actin filaments were thought to be involved in the regulation of vesicle fusion and targeting in the pollen tube. However, the molecular mechanisms that regulate the construction of apical actin structures in the pollen tube remain largely unclear. Here, we identify profilin as an important player in the regulation of actin polymerization at the apical membrane in the pollen tube. Downregulation of profilin decreased the amount of filamentous actin and induced disorganization of apical actin filaments, and reduced tip-directed vesicle transport and accumulation in the pollen tube. Direct visualization of actin dynamics revealed that the elongation of actin filaments originating at the apical membrane decreased in profilin mutant pollen tubes. Mutant profilin that is defective in binding poly-L-proline only partially rescues the actin polymerization defect in profilin mutant pollen tubes, although it fully rescues the actin turnover phenotype. We propose that profilin controls the construction of actin structures at the pollen tube tip, presumably by favoring formin-mediated actin polymerization at the apical membrane.

Functional conservation analysis and expression modes of grape anthocyanin synthesis genes responsive to low temperature stress

In grape cultivation, low temperature generally increases the expression of genes involved in synthesis of anthocyanin. In this study, multi-type structural analysis of the proteins encoded by five anthocyanin biosynthesis genes VvF3H, VvPAL, VvCHS3, VvCHS2 and VvLDOX, in addition to nine of their homologous genes revealed that proteins in grapevine shared a high similarity with that in kiwi, red orange and some other species in which the biosynthesis of anthocyanin significantly influenced by low temperature as proved by previous studies. Low temperature regulatory elements were also found in the promoter region of the grapevine genes VvCHS2, VvPAL and VvF3H. These findings indicate that the functions of anthocyanin biosynthesis genes in grapevine are conservative and might be sensitive to low temperature. In order to identify the specific expression patterns of the five anthocyanin biosynthesis genes and the changes of polyphenols, anthocyanins and flavonoids under low temperature stress. The transcription analysis of the five genes and the content of polyphenols, anthocyanins and flavonoids in grape skins were examined, by using Vitis vinifera L. cv. 'Yongyou 1' and 'Juxing' berries as experimental material and treated at 4°C and 25°C for 24h, 48 h, 72 h and 96 h. The results showed that low temperature greatly enhanced the expression of the five anthocyanin biosynthesis genes. Low temperature greatly slowed down the decomposition of polyphenol, anthocyanin, and flavonoid in grape skins. Our study also found that cv. 'Juxing' responded more sensitively to low temperature than cv. 'Yongyou 1'. All the findings would provide a basis for further study on the mechanism of anthocyanin biosynthesis under environmental stress.

Characterization of a Calmodulin-binding Transcription Factor from Strawberry (Fragaria × ananassa)

Calmodulin-binding transcription activator (CAMTA) is a calmodulin-binding transcription factor that has a broad range of functions from sensory mechanisms to regulating many growth and developmental processes. In this study, we isolated four strawberry CAMTA (FaCAMTA) genes using HMMER and BLAST analysis. The chromosome scaffold locations of these CAMTA genes in the strawberry genome were determined and the protein domain and motif organization [CG-1, transcription factor immunoglobulin, ankyrin (ANK) repeats, calmodulin-binding IQ motif) of FaCAMTAs were also assessed. All FaCAMTAs were predicted to be Ca- and calmodulin-binding proteins. The expression profiles of FaCAMTA genes were measured in different tissues and revealed distinct FaCAMTA gene expression patterns under heat, cold, and salt stress. These data not only contribute to a better understanding of the complex regulation of the FaCAMTA gene family but also provide evidence supporting the role of CAMTAs in multiple signaling pathways involved in stress responses. This investigation can provide useful information for further study.

Accumulation and post-translational modifications of plant tubulins

The microtubular cytoskeleton of plant cells provides support for several functions (including the anchoring of proteins, assembly of the mitotic spindle, cytoplasmic streaming and construction of cell walls). Both α- and β-tubulins are encoded through multigene families that are differentially expressed in different organs and tissues. To increase the variability of expression, both protein subunits are subjected to post-translational modifications, which could contribute to the assembly of specific microtubule structures. This review aims to highlight the role of specific post-translational modifications of tubulin in plant cells. We initially describe the expression and accumulation of α- and β-tubulin isoforms in different plants and at different stages of plant development. Second, we discuss the different types of post-translational modifications that, by adding or removing specific functional groups, increase the isoform heterogeneity and functional variability of tubulin. Modifications are proposed to form a 'code' that can be read by proteins interacting with microtubules. Therefore, the subpopulations of microtubules may bind to different associated proteins (motor and non-motor), thus creating the physical support for various microtubule functions.

Genome-wide identification and analysis of FK506-binding protein gene family in peach (Prunus persica)

The FKBP protein family has prolyl isomerase activity and is related in function to cyclophilins. FKBPs are known to be involved in many biological processes including hormone signaling, plant growth, and stress responses through a chaperone or an isomerization of proline residues during protein folding. The availability of complete peach genome sequences allowed the identification of 21 FKBP genes by HMMER and BLAST analyses. Scaffold locations of these FKBP genes in the peach genome were determined and the protein domain and motif organization of peach FKBPs were analyzed. The phylogenetic relationships between peach FKBPs were also assessed. The expression profiles of peach FKBP gene results revealed that most peach FKBPs were expressed in all tissues, while a few peach FKBPs were specifically expressed in some of the tissues. This data could contribute to better understanding of the complex regulation of the peach FKBP gene family, and also provide valuable information for further research in peach functional genomics.

Genome-wide identification and analysis of FK506-binding protein family gene family in strawberry (Fragaria × ananassa)

The FK506 binding proteins (FKBPs) are abundant and ubiquitous proteins belonging to the large peptidyl-prolylcis-trans isomerase superfamily. FKBPs are known to be involved in many biological processes including hormone signaling, plant growth, and stress responses through a chaperone or an isomerization of proline residues during protein folding. The availability of complete strawberry genome sequences allowed the identification of 23 FKBP genes by HMMER and blast analysis. Chromosome scaffold locations of these FKBP genes in the strawberry genome were determined and the protein domain and motif organization of FaFKBPs analyzed. The phylogenetic relationships between strawberry FKBPs were also assessed. The expression profiles of FaFKBPs genes results revealed that most FaFKBPs were expressed in all tissues, while a few FaFKBPs were specifically expressed in some of the tissues. These data not only contribute to some better understanding of the complex regulation of the strawberry FKBP gene family, but also provide valuable information for further research in strawberry functional genomics.

Boron deficiency increases the levels of cytosolic Ca(2+) and expression of Ca(2+)-related genes in Arabidopsis thaliana roots

Boron (B) deficiency affects the expressions of genes involved in major physiological processes. However, signal transduction pathway through which plants are able to sense and transmit B-deprivation signal to the nucleus is unknown. The aim of this work was to research in Arabidopsis thaliana roots whether the short-term B deficiency affects cytosolic Ca(2+) levels ([Ca(2+)]cyt) as well as expression of genes involved in Ca(2+) signaling. To visualize in vivo changes in root [Ca(2+)]cyt, Arabidopsis seedlings expressing Yellow Cameleon (YC) 3.6 were grown in a nutrient solution supplemented with 2 μM B and then transferred to a B-free medium for 24 h. Root [Ca(2+)]cyt was clearly higher in B-deficient seedlings upon 6 and 24 h of B treatments when compared to controls. Transcriptome analyses showed that transcript levels of Ca(2+) signaling-related genes were affected by B deprivation. Interestingly, Ca(2+) channel (CNGC19, cyclic nucleotide-gated ion channel) gene was strongly upregulated as early as 6 h after B deficiency. Expression levels of Ca(2+) transporter (ACA, autoinhibited Ca(2+)-ATPase; CAX, cation exchanger) genes increased when seedlings were subjected to B deficiency. Gene expressions of calmodulin-like proteins (CMLs) and Ca(2+)-dependent protein kinases (CPKs) were also overexpressed upon exposure to B starvation. Our results suggest that B deficiency causes early responses in the expression of CNGC19 Ca(2+)-influx channel, ACA- and CAX-efflux, and Ca(2+) sensor genes to regulate Ca(2+) homeostasis. It is the first time that changes in the levels of in vivo cytosolic Ca(2+) and expression of Ca(2+) channel/transporter genes are related with short-term B deficiency in Arabidopsis roots.

MAP18 regulates the direction of pollen tube growth in Arabidopsis by modulating F-actin organization

For fertilization to occur in plants, the pollen tube must be guided to enter the ovule via the micropyle. Previous reports have implicated actin filaments, actin binding proteins, and the tip-focused calcium gradient as key contributors to polar growth of pollen tubes; however, the regulation of directional pollen tube growth is largely unknown. We reported previously that Arabidopsis thaliana MICROTUBULE-ASSOCIATED PROTEIN18 (MAP18) contributes to directional cell growth and cortical microtubule organization. The preferential expression of MAP18 in pollen and in pollen tubes suggests that MAP18 also may function in pollen tube growth. In this study, we demonstrate that MAP18 functions in pollen tubes by influencing actin organization, rather than microtubule assembly. In vitro biochemical results indicate that MAP18 exhibits Ca(2+)-dependent filamentous (F)-actin-severing activity. Abnormal expression of MAP18 in map18 and MAP18 OX plants was associated with disorganization of the actin cytoskeleton in the tube apex, resulting in aberrant pollen tube growth patterns and morphologies, inaccurate micropyle targeting, and fewer fertilization events. Experiments with MAP18 mutants created by site-directed mutagenesis suggest that F-actin-severing activity is essential to the effects of MAP18 on pollen tube growth direction. Our study demonstrates that in Arabidopsis, MAP18 guides the direction of pollen tube growth by modulating actin filaments.

Characterization of the phosphoproteome of mature Arabidopsis pollen

Successful pollination depends on cell-cell communication and rapid cellular responses. In Arabidopsis, the pollen grain lands on a dry stigma, where it hydrates, germinates and grows a pollen tube that delivers the sperm cells to the female gametophyte to effect double fertilization. Various studies have emphasized that a mature, dehydrated pollen grain contains all the transcripts and proteins required for germination and initial pollen tube growth. Therefore, it is important to explore the role of post-translational modifications (here phosphorylation), through which many processes induced by pollination are probably controlled. We report here a phosphoproteomic study conducted on mature Arabidopsis pollen grains with the aim of identifying potential targets of phosphorylation. Using three enrichment chromatographies, a broad coverage of pollen phosphoproteins with 962 phosphorylated peptides corresponding to 598 phosphoproteins was obtained. Additionally, 609 confirmed phosphorylation sites were successfully mapped. Two hundred and seven of 240 phosphoproteins that were absent from the PhosPhAt database containing the empirical Arabidopsis phosphoproteome showed highly enriched expression in pollen. Gene ontology (GO) enrichment analysis of these 240 phosphoproteins shows an over-representation of GO categories crucial for pollen tube growth, suggesting that phosphorylation regulates later processes of pollen development. Moreover, motif analyses of pollen phosphopeptides showed an over-representation of motifs specific for Ca²⁺/calmodulin-dependent protein kinases, mitogen-activated protein kinases, and binding motifs for 14-3-3 proteins. Lastly, one tyrosine phosphorylation site was identified, validating the TDY dual phosphorylation motif of mitogen-activated protein kinases (MPK8/MPK15). This study provides a solid basis to further explore the role of phosphorylation during pollen development.

Characterization of the phosphoproteome of mature Arabidopsis pollen

Successful pollination depends on cell-cell communication and rapid cellular responses. In Arabidopsis, the pollen grain lands on a dry stigma, where it hydrates, germinates and grows a pollen tube that delivers the sperm cells to the female gametophyte to effect double fertilization. Various studies have emphasized that a mature, dehydrated pollen grain contains all the transcripts and proteins required for germination and initial pollen tube growth. Therefore, it is important to explore the role of post-translational modifications (here phosphorylation), through which many processes induced by pollination are probably controlled. We report here a phosphoproteomic study conducted on mature Arabidopsis pollen grains with the aim of identifying potential targets of phosphorylation. Using three enrichment chromatographies, a broad coverage of pollen phosphoproteins with 962 phosphorylated peptides corresponding to 598 phosphoproteins was obtained. Additionally, 609 confirmed phosphorylation sites were successfully mapped. Two hundred and seven of 240 phosphoproteins that were absent from the PhosPhAt database containing the empirical Arabidopsis phosphoproteome showed highly enriched expression in pollen. Gene ontology (GO) enrichment analysis of these 240 phosphoproteins shows an over-representation of GO categories crucial for pollen tube growth, suggesting that phosphorylation regulates later processes of pollen development. Moreover, motif analyses of pollen phosphopeptides showed an over-representation of motifs specific for Ca²⁺/calmodulin-dependent protein kinases, mitogen-activated protein kinases, and binding motifs for 14-3-3 proteins. Lastly, one tyrosine phosphorylation site was identified, validating the TDY dual phosphorylation motif of mitogen-activated protein kinases (MPK8/MPK15). This study provides a solid basis to further explore the role of phosphorylation during pollen development.

Genome-wide analysis and environmental response profiling of the FK506-binding protein gene family in maize (Zea mays L.)

The FK506-binding proteins (FKBPs) belong to the peptidyl-prolyl cis/trans isomerase (PPIase) superfamily, and have been implicated in a wide spectrum of biological processes, including protein folding, hormone signaling, plant growth, and stress responses. Genome-wide structural and evolutionary analyses of the entire FKBP gene family have been conducted in Arabidopsis and rice. In the present study, a genome-wide analysis was performed to identify all maize FKBP genes. The availability of complete maize genome sequences allowed for the identification of 24 FKBP genes. Chromosomal locations in the maize genome were determined and the protein domain and motif organization of ZmFKBPs analyzed. The phylogenetic relationships between maize FKBPs were also assessed. The expression profiles of ZmFKBP genes were measured under different environmental conditions and revealed distinct ZmFKBP gene expression patterns under heat, cold, salt, and drought stress. These data not only contribute to a better understanding of the complex regulation of the maize FKBP gene family, but also provide evidence supporting the role of FKBPs in multiple signaling pathways involved in stress responses. This investigation may provide valuable information for further research on stress tolerance in plants and potential strategies for enhancing maize survival under stressful conditions.

PwHAP5, a CCAAT-binding transcription factor, interacts with PwFKBP12 and plays a role in pollen tube growth orientation in Picea wilsonii

The HAP complex occurs in many eukaryotic organisms and is involved in multiple physiological processes. Here it was found that in Picea wilsonii, HAP5 (PwHAP5), a putative CCAAT-binding transcription factor gene, is involved in pollen tube development and control of tube orientation. Quantitative real-time reverse transcription-PCR showed that PwHAP5 transcripts were expressed strongly in germinating pollen and could be induced by Ca(2+). Overexpression of PwHAP5 in pollen altered pollen tube orientation, whereas the tube with PwHAP5RNAi showed normal growth without diminishing pollen tube growth. Furthermore, PwFKBP12, which encodes an FK506-binding protein (FKBP) was screened and a bimolecular fluorescence complementation assay performed to confirm the interaction of PwHAP5 and PwFKBP12 in vivo. Transient expression of PwFKBP12 in pollen showed normal pollen tube growth, whereas the tube with PwFKBP12RNAi bent. The phenotype of overexpression of HAP5 on pollen tube was restored by FKBP12. Altogether, our study supported the role of HAP5 in pollen tube development and orientation regulation and identified FKBP12 as a novel partner to interact with HAP5 involved in the process.

Alpha-tubulin (CsTUA) up-regulated during winter dormancy is a low temperature inducible gene in tea [Camellia sinensis (L.) O. Kuntze]

The present manuscript describes cloning and expression characterization of alpha-tubulin (CsTUA) gene in an evergreen tree tea [Camellia sinensis (L.) O. Kuntze] in response to winter dormancy (WD), abiotic stresses (sodium chloride, polyethylene glycol, and hydrogen peroxide) and plant growth regulators [abscisic acid (ABA), gibberellic acid (GA(3)), indole-3-butyric acid (IBA), and 6-benzylaminopurine (BA)]. CsTUA encoded a putative protein of 449 amino acids with a calculated molecular weight of 49.6 kDa and an isoelectric point (pI) of 5.09. CsTUA shared 76-84 and 90-95% identity at nucleotide and amino acid level, respectively with TUA genes from other plant species. During the period of active growth (PAG), CsTUA showed maximum expression in floral buds as compared to leaf, stem, fruit and root. Though the transcript was not detectable in the younger leaf tissue during the PAG, the expression was induced within 24 h of the low temperature (LT) treatment. The expression was not modulated by the plant growth regulators either in the tissue harvested during PAG or during WD. It was interesting to record that the expression of CsTUA was up-regulated in response to sodium chloride, polyethylene glycol, and hydrogen peroxide. Data has been discussed on the possible role of CsTUA in imparting tolerance to stresses including to LT so that the tea does not exhibit deciduous nature during winters.

Novel genes specifically expressed during the development of the male thalli and antheridia in the dioecious liverwort Pellia endiviifolia

In bryophytes (lower plants), sex determination is manifested in the gametophyte generation by the production of egg- and sperm-forming gametangia. We identified four genes specifically expressed in the male thalli of dioecious liverwort Pellia endiviifolia species B using RDA-cDNA method. These are: PenB_TUA1 coding for an α-tubulin family protein, PenB_Raba1/11 coding for a Rab family protein, PenB_HMG-box coding for an HMG-box family protein and PenB_MT coding for an unknown transcript that contains an ORF of 295 amino acid residues. The expression of identified genes shows developmental and environmental regulation. PenB_TUA1 and PenB_Raba1/11 are expressed in the male thalli, regardless of whether they develop antheridia. PenB_HMG-box and PenB_MT are exclusively expressed in the male thalli-producing antheridia while growing in the field. Moreover, two genes PenB_TUA1 and PenB_Raba1/11 are encoded only in the male genome of P. endiviifolia sp B. Our studies show for the first time the specific contribution of identified genes in the liverwort male gametophyte development. In higher plants, correct regulation of α-tubulin and Rab family genes activity is essential for tip-focused membrane trafficking and growth of the male gametophyte. Thus these genes are critical to the reproductive success of these plants. Plant HMG-box proteins bind DNA and may affect chromatin structure, promoting the assembly of nucleoprotein complexes that control DNA-dependent processes including transcription. Our results show that genes connected with the gametogenesis processes are evolutionarily conserved from the liverworts - the oldest living land plants, to higher plants.

Fitness costs linked to dinitroaniline resistance mutation in Setaria

A mutant Thr-239-Ileu at the α2-tubulin gene was found to confer resistance to dinitroanilines, a family of mitosis-disrupting herbicides. However, mutations affecting microtubule polymerization and cell division are expected to impact growth and reproduction, that is, the fitness of a resistant weed or the yield of a tolerant crop, although it has not been demonstrated yet. This study was designed to test this hypothesis for the growth and reproduction of near-isogenic resistant and susceptible materials that were created in F(2) and F(3) generations after a Setaria viridis x S. italica cross. Differential growth was noticeable at the very onset of seedling growth. The homozygous resistant plants, grown both in a greenhouse cabinet and in the field, were smaller and had lower 1000-grain weight and therefore a lower yield. This fitness penalty is certainly due to modified cell division kinetics. Although the presence of the mutant allele accounted for 20% yield losses, there were also measurable benefits of dinitroaniline resistance, and these benefits are discussed.

Establishment of the male germline and sperm cell movement during pollen germination and tube growth in maize

Two sperm cells are required to achieve double fertilization in flowering plants (angiosperms). In contrast to animals and lower plants such as mosses and ferns, sperm cells of flowering plants (angiosperms) are immobile and are transported to the female gametes (egg and central cell) via the pollen tube. The two sperm cells arise from the generative pollen cell either within the pollen grain or after germination inside the pollen tube. While pollen tube growth and sperm behaviour has been intensively investigated in model plant species such as tobacco and lily, little is know about sperm dynamics and behaviour during pollen germination, tube growth and sperm release in grasses. In the March issue of Journal of Experimental Botany, we have reported about the sporophytic and gametophytic control of pollen tube germination, growth and guidance in maize.1 Five progamic phases were distinguished involving various prezygotic crossing barriers before sperm cell delivery inside the female gametophyte takes place. Using live cell imaging and a generative cell-specific promoter driving α-tubulin-YFP expression in the male germline, we report here the formation of the male germline inside the pollen grain and the sperm behaviour during pollen germination and their movement dynamics during tube growth in maize.

Changes in the accumulation of alpha- and beta-tubulin during bud development in Vitis vinifera L

Microtubules play important roles during growth and morphogenesis of plant cells. Multiple isoforms of alpha- and beta-tubulin accumulate in higher plant cells and originate either by transcription of different genes or by post-translational modifications. The use of different tubulin isoforms involves the binding of microtubules to different associated proteins and therefore generates microtubules with different organizations and functions. Tubulin isoforms are differentially expressed in vegetative and reproductive structures according to the developmental program of plants. In grapevine (Vitis vinifera L.), vegetative and reproductive structures appear on the same stem, making this plant species an excellent model to study the accumulation of tubulin isoforms. Proteins were extracted from grapevine samples (buds, leaves, flowers and tendrils) using an optimized extraction protocol, separated by two-dimensional electrophoresis and analyzed by immunoblot with anti-tubulin antibodies. We identified eight alpha-tubulin and seven beta-tubulin isoforms with pI around 4.8-5 that group into separate clusters. More acidic alpha-tubulin isoforms were detected in buds, while more basic alpha-isoforms were prevalently found in tendrils and flowers. Similarly, more acidic beta-tubulin isoforms were used in the bud stage while a basic beta-tubulin isoform was essentially used in leaves and two central beta-tubulin isoforms were characteristically used in tendrils and flowers. Acetylated alpha-tubulin was not detected in any sample while tyrosinated alpha-tubulin was essentially found in large latent buds and in bursting buds in association with a distinct subset of tubulin isoforms. The implication of these data on the use of different tubulin isoforms during grapevine development is discussed.