Sequence analysis of three members of the maize polygalacturonase gene family expressed during pollen development

Genome-Wide Identification and Characterization of Polygalacturonase Gene Family in Maize (Zea mays L.)

Polygalacturonase (PG, EC 3.2.1.15) is a crucial enzyme for pectin degradation and is involved in various developmental processes such as fruit ripening, pollen development, cell expansion, and organ abscission. However, information on the PG gene family in the maize (Zea mays L.) genome and the specific members involved in maize anther development are still lacking. In this study, we identified 55 PG family genes from the maize genome and further characterized their evolutionary relationship and expression patterns. Phylogenetic analysis revealed that ZmPGs are grouped into six Clades, and gene structures of the same Clade are highly conserved, suggesting their functional conservation. The ZmPGs are randomly distributed across maize chromosomes, and collinearity analysis showed that many ZmPGs might be derived from tandem duplications and segmental duplications, and these genes are under purifying selection. Furthermore, gene expression analysis provided insights into possible functional divergence among ZmPGs. Based on the RNA-seq data analysis, we found that many ZmPGs are expressed in various tissues while 18 ZmPGs are highly expressed in maize anther, and their detailed expression profiles in different anther developmental stages were further investigated by using RT-qPCR analysis. These results provide valuable information for further functional characterization and application of the ZmPGs in maize.

Comprehensive analysis of polygalacturonase gene family highlights candidate genes related to pollen development and male fertility in wheat (Triticum aestivum L.)

Four polygalacturonase gene family members were highlighted that contribute to elucidate the roles of polygalacturonase during the fertility conversion process in male-sterile wheat. Polygalacturonase (PG) belongs to a large family of hydrolases with important functions in cell separation during plant growth and development via the degradation of pectin. Specific expressed PGs in anthers may be significant for male sterility research and hybrid wheat breeding, but they have not been characterized in wheat (Triticum aestivum L.). In this study, we systematically studied the PG gene family using the latest published wheat reference genomic information. In total, 113 wheat PG genes were identified, which could be classified into six categories A-F according to their structure characteristics and phylogenetic comparisons with Arabidopsis and rice. Polyploidy and segmental duplications in wheat were proved to be mainly responsible for the expansion of the wheat PG gene family. RNA-seq showed that TaPGs have specific temporal and spatial expression characteristics, in which 12 TaPGs with spike-specific expression patterns were detected by qRT-PCR in different fertility anthers of KTM3315A, a thermo-sensitive cytoplasmic male-sterile wheat. Four of them specific upregulated (TaPG09, TaPG95, and TaPG93) or downregulated (TaPG87) at trinucleate stage of fertile anthers, and further aligning with the homologous in Arabidopsis revealed that they may undertake functions such as anther dehiscence, separation of pollen, pollen development, and pollen tube elongation, thereby inducing male fertility conversion in KTM3315A. These findings facilitate function investigations of the wheat PG gene family and provide new insights into the fertility conversion mechanism in male-sterile wheat.

A maize polygalacturonase functions as a suppressor of programmed cell death in plants

BACKGROUND

The hypersensitive defense response (HR) in plants is a fast, localized necrotic response around the point of pathogen ingress. HR is usually triggered by a pathogen recognition event mediated by a nucleotide-binding site, leucine-rich repeat (NLR) protein. The autoactive maize NLR gene Rp1-D21 confers a spontaneous HR response in the absence of pathogen recognition. Previous work identified a set of loci associated with variation in the strength of Rp1-D21-induced HR. A polygalacturonase gene homolog, here termed ZmPGH1, was identified as a possible causal gene at one of these loci on chromosome 7.

RESULTS

Expression of ZmPGH1 inhibited the HR-inducing activity of both Rp1-D21 and that of another autoactive NLR, RPM1(D505V), in a Nicotiana benthamiana transient expression assay system. Overexpression of ZmPGH1 in a transposon insertion line of maize was associated with suppression of chemically-induced programmed cell death and with suppression of HR induced by Rp1-D21 in maize plants grown in the field.

CONCLUSIONS

ZmPGH1 functions as a suppressor of programmed cell death induced by at least two autoactive NLR proteins and by two chemical inducers. These findings deepen our understanding of the control of the HR in plants.

Molecular features of grass allergens and development of biotechnological approaches for allergy prevention

Allergic diseases are characterized by elevated allergen-specific IgE and excessive inflammatory cell responses. Among the reported plant allergens, grass pollen and grain allergens, derived from agriculturally important members of the Poaceae family such as rice, wheat and barley, are the most dominant and difficult to prevent. Although many allergen homologs have been predicted from species such as wheat and timothy grass, fundamental aspects such as the evolution and function of plant pollen allergens remain largely unclear. With the development of genetic engineering and genomics, more primary sequences, functions and structures of plant allergens have been uncovered, and molecular component-based allergen-specific immunotherapies are being developed. In this review, we aim to provide an update on (i) the distribution and importance of pollen and grain allergens of the Poaceae family, (ii) the origin and evolution, and functional aspects of plant pollen allergens, (iii) developments of allergen-specific immunotherapy for pollen allergy using biotechnology and (iv) development of less allergenic plants using gene engineering techniques. We also discuss future trends in revealing fundamental aspects of grass pollen allergens and possible biotechnological approaches to reduce the amount of pollen allergens in grasses.

In vitro protein profiles in the early and late stages of Douglas-fir xylogenesis

The process of wood formation is of great interest to control and manipulate wood quality for economically important gymnosperms. A Douglas-fir tissue culture system was developed that could be induced to differentiate into tracheary elements (fibers) making it possible to monitor xylogenesis in vitro by a proteomics approach. Two proteomes were analyzed and compared, one from an early and one from a late stage of the fiber differentiation process. After 18 weeks in a differentiation-inducing medium, 80% of the callus cells were elongated while 20% showed advanced spiral thickening indicating full wood fiber differentiation. Based on 2D electrophoresis, MS, and data analyses (data are available via ProteomeXchange with identifier PXD001484.), it was shown that in nondifferentiated callus (representing an early stage of development), proteins related to protein metabolism, cellular energy, and primary cell wall metabolism were abundant. By comparison, in cells actively differentiating wood fibers (representing a late stage of development), proteins involved in cell wall polysaccharide biosynthesis predominated together with housekeeping and stress-associated proteins.

HvPG1 and ECA1: two genes activated transcriptionally in the transition of barley microspores from the gametophytic to the embryogenic pathway

Microspores genetically programmed to produce male gametes can be switched to the embryogenic pathway to give rise to haploid embryos. Microspore embryogenesis is usually induced in barley by stress pre-treatment applied to vacuolated microspores. We studied the expression of two genes during the early stages of microspore embryogenesis to gain further insight into the microspore transition from the gametophytic to the embryogenic pathway. RT-PCR together with in situ hybridization on sections (ISH) and whole-mount in situ hybridization (WISH) were used to analyse the expression of the early-culture abundant gene (ECA1), which is expressed in barley during microspore embryogenesis, and a polygalacturonase gene (HvPG1), a late pollen gene expressed during gametogenesis only after microspore division. Both ECA1 and HvPG1 genes were transcriptionally active after stress pre-treatment in the same populations of microspore-derived structures, representing the sporophytically induced ones. ECA1 transcripts were also detected after 3 days' culture. Our results point to the possibility of using ECA1 gene expression as a marker for the induction of microspore embryogenesis and the earliest stages of this process. Finally, we demonstrate that WISH is a suitable technique for studying gene expression in embryogenic microspore populations and, because different structures can be examined individually, is an appropriate complement to transcriptomic profile analyses in the study of early microspore embryogenesis.

Functional analysis of a pollen-expressed polygalacturonase gene BcMF6 in Chinese cabbage (Brassica campestris L. ssp. chinensis Makino)

In our earlier work, a pollen-expressed polygalacturonase gene BcMF6 was isolated from floral bud of Chinese cabbage (Brassica campestris L. ssp. chinensis Makino) by cDNA-amplified fragment length polymorphism (cDNA-AFLP) transcript profiling and rapid amplification of cDNA ends (RACE). To unravel the biological function of BcMF6 gene, the antisense fragment from the BcMF6 gene with A9 promoter and CaMV35S promoter was transferred into flowering Chinese cabbage (B. campestris ssp. chinensis var. parachinensis). Out of transgenic plants transformed with the antisense gene constructed from the BcMF6, transgenic line with A9 promoter have a similar appearance to that with CaMV35S promoter. Morphological investigations showed that the transgenic plants developed the smaller floral organ with thin anther and less pollen. Pollen germination test indicated that only near 50% the pollen from the transgenic line could normally germinate. Further scanning electron microspore analysis of transgenic plants confirmed that half of pollen was abnormal. Cytological comparisons of microspore development also demonstrated that process of microsporogenesis was held up, microspores maturation was disrupted and pollen grain fail to separate, finally. In a word, the present study revealed that BcMF6, as a polygalacturonase gene, has a role in pollen maturation and pollen tube growth.

Proteome mapping of mature pollen of Arabidopsis thaliana

The male gametophyte of Arabidopsis is a three-celled pollen grain that is thought to contain almost all the mRNAs needed for germination and rapid pollen tube growth. We generated a reference map of the Arabidopsis mature pollen proteome by using multiple protein extraction techniques followed by 2-DE and ESI-MS/MS. We identified 135 distinct proteins from a total of 179 protein spots. We found that half of the identified proteins are involved in metabolism (20%), energy generation (17%), or cell structure (12%); these percentages are similar to those determined for the pollen transcriptome and this similarity is consistent with the idea that in addition to the mRNAs, the mature pollen grain contains proteins necessary for germination and rapid pollen tube growth. We identified ten proteins of unknown function, three of which are flower- or pollen-specific, and we identified nine proteins whose RNAs were absent from the transcriptome, seven of which are involved in metabolism, energy generation, or cell wall structure. Our work complements and extends recent analyses of the pollen transcriptome.

Characterization of a pollen-preferential gene, BAN102, from Chinese cabbage

We isolated and characterized a pollen-preferential gene, BAN102, from Chinese cabbage and analyzed the activity of its promoter. There were three or four copies of the BAN102 gene in the Chinese cabbage genome that specifically expressed in pollen and pollen tube. There were 2137 bp of BAN102 genomic clone comprising 186 bp of protein coding region, and 1178 bp of 5' and 773 bp of 3' non-coding regions. TATA box were located at 1071 nt of the promoter region while the polyadenylation signal and polyadenylation site were at 1470 and 1486 nt of the 3' non-coding region. BLAST search of BAN102 sequence showed that coding region of BAN102 gene was the greatest percent similarity with arabinogalactan protein (AGP23) gene from Arabidopsis thaliana. Promoter analysis using GUS gene as a reporter showed that the pollen-specificity of BAN102 resided within the -112 to -44 bp of proximal promoter from the transient expression in tobacco and Chinese cabbage plants.

Purification and characterization of a novel peptidase (IImes) from mesquite (Prosopis velutina) pollen

Although the mesquite plant (Prosopis velutina) is not as widely distributed as some other allergenic species, its pollen can induce serious pollinosis in areas where it is localized. We previously isolated and characterized a peptidase from mesquite pollen with trypsin-like specificity (peptidase Imes) (Matheson, N., Schmidt, J., and Travis, J. (1995) Am. J. Respir. Cell Mol. Biol. 12, 441-448). Now we have characterized a second enzyme with specificity for hydrophobic residues (mesquite pollen peptidase IImes). This enzyme has a molecular mass near 92 kDa and activity that was not affected by reducing or chelating agents but was inhibited by specific synthetic serine proteinase inhibitors and the aminopeptidase inhibitor bestatin. However, it was not inhibited by human plasma proteinase inhibitors, nor did it inactivate any of those tested. The enzyme possessed amidolytic activity against p-nitroanilide substrates most effectively after alanine residues and also displayed aminopeptidase activity against non-p-nitroanilide peptides with a preference for phenylalanine. This specificity for hydrophobic amino acid residues was corroborated by inhibition studies with chloromethyl ketone and organophosphonate inhibitors. More interesting from a physiological point of view is that the bioactive peptides, angiotensins I and II and vasoactive intestinal peptide, were also hydrolyzed rapidly, indicating an ability of peptidase IImes to act also as an oligopeptidase. Because these bioactive peptides play a role in the inflammatory responses in allergic asthma, our data suggest that the purified mesquite pollen peptidase IImes may be involved in the degradation of neuro- and vasoactive peptides during pollen-initiated allergic reactions.

Characterization of a tobacco gene encoding a pollen-specific polygalacturonase

We report here the isolation and characterization of a gene which is specifically expressed during late pollen development in Nicotiana tabacum L. cv. Havana and which exhibits homology to bacterial, fungal and plant polygalacturonases. This gene is ca. 4.3 kb, from the transcription start-site to the 3' polyadenylation-site sequences. It contains three introns of 620, 706 and 1400 bp and encodes a 1.5 kb message that contains an A-rich 5'-untranslated-leader sequence of 81 bases and a variable-length 3'-untranslated sequence of between 180 and 320 bases. Located within intron 3 is a 414 bp sequence which exhibits 79% homology to a sequence within the endochitinase gene; both sequences share the same internal repeat structure and exhibit features consistent with them being defective transposable elements. The predicted protein sequence coded for by Npg1 shows, in addition to a number of highly conserved cysteines, four conserved domains with the bacterial and fungal polygalacturonase genes. The pollen-specific polygalacturonases as a group can be distinguished from the fruit-ripening polygalacturonases by a number of criteria. It is suggested that these differences reflect the functional differences between plant endo- and exo-polygalacturonases. Npg1 is one of a two-member gene family expressed predominantly in the male gametophyte upon first microspore mitosis. From expression studies of promoter::GUS transgenes it is clear that the -744 bp to +74/+85 bp of Npg1 sequence (with respect to the transcription start site) is sufficient to drive the expression of the GUS reporter gene in a manner that reflects the spatial and temporal expression of Npg1 as determined by dot-blot and northern analysis.

Isolation and characterization of a polygalacturonase gene highly expressed in Brassica napus pollen

A cDNA clone, Sta 44-4, corresponding to a mRNA highly expressed in Brassica napus cv. Westar stamens, was isolated by differential screening and characterized. Northern blot and in situ analyses demonstrated that Sta 44-4 is synthesized in pollen beginning at the late uninucleate stage and reaches a maximum in trinucleate microspores. Sta 44-4 displayed significant sequence similarity to known pollen polygalacturonase genes. The B. napus pollen polygalacturonase gene was shown to be part of a small gene family and to display some polymorphism among different cultivars.

Molecular characterization of one of the maize polygalacturonase gene family members which are expressed during late pollen development

A gene exhibiting homology to the polygalacturonases of several species, including tomato and Oenothera, has been shown by RNA dot-blot analysis and in situ hybridization experiments to be expressed post-first microspore mitosis in maize. A 2.87 kbp section of the promoter fused to E. coli beta-glucuronidase (uidA) coding sequence conferred the correct spatial and temporal expression in transgenic tobacco plants. However, low levels of expression were detected in other tissues, and in particular in the tissues surrounding the vascular branch points of leaf nodes. The maize polygalacturonase gene is one member of a highly conserved gene family. The lack of detectable expression in sporophytic tissues and the isolation of a number of related cDNAs from maize suggests that all expressed members of this family show the same spatial and temporal regulation.