Evaluation of rice promoters conferring pollen-specific expression in a heterologous system, Arabidopsis

Transcription factors WRKY2 and WRKY34 control LATERAL ORGAN BOUNDARIES DOMAIN10 expression in pollen vegetative cell nuclei

The intricate regulation of gene expression determining cell fate during male gametogenesis involves a complex interplay of multiple transcriptional regulators. In Arabidopsis (Arabidopsis thaliana), the LATERAL ORGAN BOUNDARIES DOMAIN 10 (LBD10) transcription factor is prominent in early microspores and both the germ and vegetative cells of bicellular pollen, playing an important role in pollen development. However, in mature pollen, LBD10 exclusively localizes in the vegetative cell nucleus (VCN). Here, we identify cis-acting elements and trans-acting factors responsible for the specific expression of LBD10 in the VCN during pollen maturation. Using a series of LBD10 promoter deletion constructs fused with GUS or GFP reporters, we pinpoint two crucial core promoter sequences. These sequences are situated within two 200 bp regions upstream of the start codon and independently govern LBD10 expression in the VCN. We demonstrate that a W-box motif (AGTCAC) at -770 bp is essential for activating the expression of LBD10 in vegetative cells during pollen maturation. Our transient gene expression assays using Arabidopsis protoplasts and chromatin immunoprecipitation assays show that the transcription factors WRKY2 and WRKY34 recognize the LBD10 promoter region containing W-box motifs. Collectively, our findings suggest that WRKY2 and WRKY34 binding to the W-box motifs plays a role in the VCN-specific expression of LBD10 in pollen. This interaction may contribute to male gametophyte development, shedding light on the intricate regulatory network governing this critical biological process.

Rapid Identification of Pollen- and Anther-Specific Genes in Response to High-Temperature Stress Based on Transcriptome Profiling Analysis in Cotton

Anther indehiscence and pollen sterility caused by high temperature (HT) stress have become a major problem that decreases the yield of cotton. Pollen- and anther-specific genes play a critical role in the process of male reproduction and the response to HT stress. In order to identify pollen-specific genes that respond to HT stress, a comparative transcriptome profiling analysis was performed in the pollen and anthers of Gossypium hirsutum HT-sensitive Line H05 against other tissue types under normal temperature (NT) conditions, and the analysis of a differentially expressed gene was conducted in the pollen of H05 under NT and HT conditions. In total, we identified 1111 pollen-specific genes (PSGs), 1066 anther-specific genes (ASGs), and 833 pollen differentially expressed genes (DEGs). Moreover, we found that the late stage of anther included more anther- and pollen-specific genes (APSGs). Stress-related cis-regulatory elements (CREs) and hormone-responsive CREs are enriched in the promoters of APSGs, suggesting that APSGs may respond to HT stress. However, 833 pollen DEGs had only 10 common genes with 1111 PSGs, indicating that PSGs are mainly involved in the processes of pollen development and do not respond to HT stress. Promoters of these 10 common genes are enriched for stress-related CREs and MeJA-responsive CREs, suggesting that these 10 common genes are involved in the process of pollen development while responding to HT stress. This study provides a pathway for rapidly identifying cotton pollen-specific genes that respond to HT stress.

A Rapid Pipeline for Pollen- and Anther-Specific Gene Discovery Based on Transcriptome Profiling Analysis of Maize Tissues

Recently, crop breeders have widely adopted a new biotechnology-based process, termed Seed Production Technology (SPT), to produce hybrid varieties. The SPT does not produce nuclear male-sterile lines, and instead utilizes transgenic SPT maintainer lines to pollinate male-sterile plants for propagation of nuclear-recessive male-sterile lines. A late-stage pollen-specific promoter is an essential component of the pollen-inactivating cassette used by the SPT maintainers. While a number of plant pollen-specific promoters have been reported so far, their usefulness in SPT has remained limited. To increase the repertoire of pollen-specific promoters for the maize community, we conducted a comprehensive comparative analysis of transcriptome profiles of mature pollen and mature anthers against other tissue types. We found that maize pollen has much less expressed genes (>1 FPKM) than other tissue types, but the pollen grain has a large set of distinct genes, called pollen-specific genes, which are exclusively or much higher (100 folds) expressed in pollen than other tissue types. Utilizing transcript abundance and correlation coefficient analysis, 1215 mature pollen-specific (MPS) genes and 1009 mature anther-specific (MAS) genes were identified in B73 transcriptome. These two gene sets had similar GO term and KEGG pathway enrichment patterns, indicating that their members share similar functions in the maize reproductive process. Of the genes, 623 were shared between the two sets, called mature anther- and pollen-specific (MAPS) genes, which represent the late-stage pollen-specific genes of the maize genome. Functional annotation analysis of MAPS showed that 447 MAPS genes (71.7% of MAPS) belonged to genes encoding pollen allergen protein. Their 2-kb promoters were analyzed for cis-element enrichment and six well-known pollen-specific cis-elements (AGAAA, TCCACCA, TGTGGTT, [TA]AAAG, AAATGA, and TTTCT) were found highly enriched in the promoters of MAPS. Interestingly, JA-responsive cis-element GCC box (GCCGCC) and ABA-responsive cis-element-coupling element1 (ABRE-CE1, CCACC) were also found enriched in the MAPS promoters, indicating that JA and ABA signaling likely regulate pollen-specific MAPS expression. This study describes a robust and straightforward pipeline to discover pollen-specific promotes from publicly available data while providing maize breeders and the maize industry a number of late-stage (mature) pollen-specific promoters for use in SPT for hybrid breeding and seed production.

Sequence and functional analysis of MIR319 promoter homologs from Brassica juncea reveals regulatory diversification and altered expression under stress

KEY MESSAGE

Extensive regulatory divergence during development, abiotic stress and ABA regime observed amongst promoter homologs and homeologs of MIR319 from Brassica juncea. Gene duplication followed by sub-functionalization, neo-functionalization, and pseudogenization are routes to functional and adaptive diversification. The influence of polyploidy on protein-coding genes is well investigated but little is known about their impact on transcriptional regulation of MIRNA gene family. The present study was therefore performed with an aim to uncover regulatory diversification of MIR319 homologs and homeologs in Brassica juncea. We employed comparative genomics to identify and isolate six promoter homologs of MIR319 from B. juncea. Regulatory diversification was studied using analysis of reporter activity driven by BjMIR319 promoters in a heterologous system employing promoter-reporter fusion constructs. MIR319 is known to play important roles in leaf and flower development, and multiple stress responses. Reporter activity was therefore monitored during development, hormonal and stress regimes. In-silico analyses revealed differential distribution of cis-regulatory motifs and functional analysis revealed distinct spatiotemporal expression patterns. The significance of presence of selected cis-regulatory motifs corresponding to heat, cold, salt and ABA stress were further functionally validated. It was observed that promoter of Bj -MIR319a-A01 was upregulated in response to cold and salt stress, while promoter of Bj -MIR319c-A04 (D1) and Bj -MIR319c-A05 (FL) were downregulated in response to high temperature. In summary, comparative analysis of homologous promoters from Brassica juncea, an allopolyploid revealed extensive sequence and functional diversity. Spatiotemporal activity of reporter gene driven by BjMIR319 promoter was distinct, and partially overlapping with from those reported previously for A. thaliana. The present study clearly demonstrates regulatory divergence amongst promoter homologs of MIR319 in Brassica juncea during development and stress response, and underlines the urgent need for dissection of promoter function and detailed characterization including identification of interacting trans-factors. Genbank accession numbers: MT379853-MT379858.

Efficient Gene Stacking in Rice Using the GAANTRY System

Genetic engineering of rice provides a means for improving rice grain quality and yield, and the introduction and expression of multiple genes can produce new traits that would otherwise be difficult to obtain through conventional breeding. GAANTRY (Gene Assembly in Agrobacterium by Nucleic acid Transfer using Recombinase technologY) was previously shown to be a precise and robust system to stably stack ten genes (28 kilobases (kb)) within an Agrobacterium virulence plasmid Transfer-DNA (T-DNA) and obtain high-quality Arabidopsis and potato transgenic events. To determine whether the GAANTRY system can be used to engineer a monocotyledonous crop, two new T-DNA constructs, carrying five (16.9 kb) or eleven (37.4 kb) cargo sequences were assembled and transformed into rice. Characterization of 53 independent transgenic events demonstrated that more than 50% of the plants carried all of the desired cargo sequences and exhibited the introduced traits. Additionally, more than 18% of the lines were high-quality events containing a single copy of the introduced transgenes and were free of sequences from outside of the T-DNA. Therefore, GAANTRY provides a simple, precise and versatile tool for transgene stacking in rice and potentially other cereal grain crops.

Identification of the Core Pollen-Specific Regulation in the Rice OsSUT3 Promoter

The regulatory mechanisms of pollen development have potential value for applications in agriculture, such as better understanding plant reproductive regularity. Pollen-specific promoters are of vital importance for the ectopic expression of functional genes associated with pollen development in plants. However, there is a limited number of successful applications using pollen-specific promoters in genetic engineering for crop breeding and hybrid generation. Our previous work led to the identification and isolation of the OsSUT3 promoter from rice. In this study, to analyze the effects of different putative regulatory motifs in the OsSUT3 promoter, a series of promoter deletions were fused to a GUS reporter gene and then stably introduced into rice and Arabidopsis. Histochemical GUS analysis of transgenic plants revealed that p385 (from -385 to -1) specifically mediated maximal GUS expression in pollen tissues. The S region (from -385 to -203) was the key region for controlling the pollen-specific expression of a downstream gene. The E1 (-967 to -606), E2 (-202 to -120), and E3 (-119 to -1) regions enhanced ectopic promoter activity to different degrees. Moreover, the p385 promoter could alter the expression pattern of the 35S promoter and improve its activity when they were fused together. In summary, the p385 promoter, a short and high-activity promoter, can function to drive pollen-specific expression of transgenes in monocotyledon and dicotyledon transformation experiments.

Genetic engineering of parthenocarpic tomato plants using transient SlIAA9 knockdown by novel tissue-specific promoters

Parthenocarpy is the development of an ovary into a seedless fruit without pollination. The ubiquitous downregulation of SlIAA9 induces not only parthenocarpic fruit formation but also an abnormal vegetative phenotype. To make parthenocarpic transgenic tomato plants without unwanted phenotypes, we found two genes, namely, Solyc03g007780 and Solyc02g067760, expressed in ovary tissue but not in vegetative tissues. Solyc03g007780 was expressed in developing ovaries and anthers. Solyc02g067760 mRNA was detected in whole-flower tissues. The promoters of Solyc03g007780 (Psol80) and Solyc02g067760 (Psol60) predominantly induced the expression of genes in the ovule, placenta, endocarp and pollen and in whole-flower tissues, respectively. Psol80/60-SlIAA9i lines, created for SlIAA9-RNA interference controlled by two promoters, successfully formed parthenocarpic fruits without pleiotropic effects in vegetative tissues. Downregulation of SlIAA9, responsible for parthenocarpic fruit formation, was observed in ovules rather than ovaries in the Psol80/60-SlIAA9i lines. Although the weight of parthenocarpic fruits of the Psol80/60-SlIAA9i lines was lower than the weight of pollinated fruits of the wild type (WT), the parthenocarpic fruits presented redder and more saturated colors and higher levels of total soluble solids and titratable acidity than the WT fruits.

Mapping of QTL for total spikelet number per spike on chromosome 2D in wheat using a high-density genetic map

Total spikelet number per spike (TSS) is one of the key components of grain yield in wheat. Chromosome (chr.) 2D contains numerous genes that control TSS. In this study, we evaluated 138 F₈ recombinant inbred lines (RILs) derived from an F₂ population of a synthetic hexaploid wheat line (SHW-L1) and a common wheat cultivar (Chuanmai 32) for TSS in six different environments. To identify quantitative trait loci (QTL) for TSS, we constructed an integrated high-density genetic map of chr. 2D containing two simple sequence repeats, 35 diversity array technology markers, and 143 single nucleotide polymorphisms. We identified three stable QTL for TSS that individually explained 9.7–19.2% of the phenotypic variation and predicted 23 putative candidate genes within the QTL mapping interval. Overall, our results provide insight into the genetic basis of TSS in synthetic hexaploid wheat that may be useful in breeding high-yielding wheat cultivars.

Analysis of genes encoding seed storage proteins (SSPs) in chickpea (Cicer arietinum L.) reveals co-expressing transcription factors and a seed-specific promoter

Improvement of the quality and quantity of chickpea seed protein can be greatly facilitated by an understanding of the genic organization and the genetic architecture of the genes encoding seed storage proteins (SSPs). The aim of this study was to provide a comprehensive analysis of the chickpea SSP genes, putative co-expressing transcription factors (TFs), and to identify a seed-specific SSP gene promoter. A genome-wide identification of SSP genes in chickpea led to the identification of 21 non-redundant SSP encoding genes located on 6 chromosomes. Phylogenetic analysis grouped SSP genes into 3 subgroups where members within the same clade demonstrated similar motif composition and intron-exon organization. Tandem duplications were identified to be the major contributors to the expansion of the SSP gene family in chickpea. Co-expression analysis revealed 14 TFs having expression profiles similar to the SSP genes that included members of important TF families that are known to regulate seed development. Expression analysis of SSP genes and TFs revealed significantly higher expression in late stages of seed development as well as in high seed protein content (HPC) genotypes. In silico analysis of the promoter regions of the SSP encoding genes revealed several seed-specific cis-regulatory elements such as RY repeats, ACGT motifs, CAANTG, and GCN4. A candidate promoter was analyzed for seed specificity by generating stable transgenics in Arabidopsis. Overall, this study provides a useful resource to explore the regulatory networks involved in SSP synthesis and/or accumulation for utilization in developing nutritionally improved chickpea genotypes.

Genome-wide analyses of late pollen-preferred genes conserved in various rice cultivars and functional identification of a gene involved in the key processes of late pollen development

BACKGROUND

Understanding late pollen development, including the maturation and pollination process, is a key component in maintaining crop yields. Transcriptome data obtained through microarray or RNA-seq technologies can provide useful insight into those developmental processes. Six series of microarray data from a public transcriptome database, the Gene Expression Omnibus of the National Center for Biotechnology Information, are related to anther and pollen development.

RESULTS

We performed a systematic and functional study across the rice genome of genes that are preferentially expressed in the late stages of pollen development, including maturation and germination. By comparing the transcriptomes of sporophytes and male gametes over time, we identified 627 late pollen-preferred genes that are conserved among japonica and indica rice cultivars. Functional classification analysis with a MapMan tool kit revealed a significant association between cell wall organization/metabolism and mature pollen grains. Comparative analysis of rice and Arabidopsis demonstrated that genes involved in cell wall modifications and the metabolism of major carbohydrates are unique to rice. We used the GUS reporter system to monitor the expression of eight of those genes. In addition, we evaluated the significance of our candidate genes, using T-DNA insertional mutant population and the CRISPR/Cas9 system. Mutants from T-DNA insertion and CRISPR/Cas9 systems of a rice gene encoding glycerophosphoryl diester phosphodiesterase are defective in their male gamete transfer.

CONCLUSION

Through the global analyses of the late pollen-preferred genes from rice, we found several biological features of these genes. First, biological process related to cell wall organization and modification is over-represented in these genes to support rapid tube growth. Second, comparative analysis of late pollen preferred genes between rice and Arabidopsis provide a significant insight on the evolutional disparateness in cell wall biogenesis and storage reserves of pollen. In addition, these candidates might be useful targets for future examinations of late pollen development, and will be a valuable resource for accelerating the understanding of molecular mechanisms for pollen maturation and germination processes in rice.

Application of rice microspore-preferred promoters to manipulate early pollen development in Arabidopsis: a heterologous system

Rice microspore-promoters. Based on microarray data analyzed for developing anthers and pollen grains, we identified nine rice microspore-preferred (RMP) genes, designated RMP1 through RMP9. To extend their biotechnological applicability, we then investigated the activity of RMP promoters originating from monocotyledonous rice in a heterologous system of dicotyledonous Arabidopsis. Expression of GUS was significantly induced in transgenic plants from the microspore to the mature pollen stages and was driven by the RMP1, RMP3, RMP4, RMP5, and RMP9 promoters. We found it interesting that, whereas RMP2 and RMP6 directed GUS expression in microspore at the early unicellular and bicellular stages, RMP7 and RMP8 seemed to be expressed at the late tricellular and mature pollen stages. Moreover, GUS was expressed in seven promoters, RMP3 through RMP9, during the seedling stage, in immature leaves, cotyledons, and roots. To confirm microspore-specific expression, we used complementation analysis with an Arabidopsis male-specific gametophytic mutant, sidecar pollen-2 (scp-2), to verify the activity of three promoters. That mutant shows defects in microspore development prior to pollen mitosis I. These results provide strong evidence that the SIDECAR POLLEN gene, driven by RMP promoters, successfully complements the scp-2 mutation, and they strongly suggest that these promoters can potentially be applied for manipulating the expression of target genes at the microspore stage in various species.

Horizontal gene transfer is more frequent with increased heterotrophy and contributes to parasite adaptation

Horizontal gene transfer (HGT) is the transfer of genetic material across species boundaries and has been a driving force in prokaryotic evolution. HGT involving eukaryotes appears to be much less frequent, and the functional implications of HGT in eukaryotes are poorly understood. We test the hypothesis that parasitic plants, because of their intimate feeding contacts with host plant tissues, are especially prone to horizontal gene acquisition. We sought evidence of HGTs in transcriptomes of three parasitic members of Orobanchaceae, a plant family containing species spanning the full spectrum of parasitic capabilities, plus the free-living Lindenbergia Following initial phylogenetic detection and an extensive validation procedure, 52 high-confidence horizontal transfer events were detected, often from lineages of known host plants and with an increasing number of HGT events in species with the greatest parasitic dependence. Analyses of intron sequences in putative donor and recipient lineages provide evidence for integration of genomic fragments far more often than retro-processed RNA sequences. Purifying selection predominates in functionally transferred sequences, with a small fraction of adaptively evolving sites. HGT-acquired genes are preferentially expressed in the haustorium-the organ of parasitic plants-and are strongly biased in predicted gene functions, suggesting that expression products of horizontally acquired genes are contributing to the unique adaptive feeding structure of parasitic plants.

Genome-wide identification and analysis of rice genes preferentially expressed in pollen at an early developmental stage

Microspore production using endogenous developmental programs has not been well studied. The main limitation is the difficulty in identifying genes preferentially expressed in pollen grains at early stages. To overcome this limitation, we collected transcriptome data from anthers and microspore/pollen and performed meta-expression analysis. Subsequently, we identified 410 genes showing preferential expression patterns in early developing pollen samples of both japonica and indica cultivars. The expression patterns of these genes are distinguishable from genes showing pollen mother cell or tapetum-preferred expression patterns. Gene Ontology enrichment and MapMan analyses indicated that microspores in rice are closely linked with protein degradation, nucleotide metabolism, and DNA biosynthesis and regulation, while the pollen mother cell or tapetum are strongly associated with cell wall metabolism, lipid metabolism, secondary metabolism, and RNA biosynthesis and regulation. We also generated transgenic lines under the control of the promoters of eight microspore-preferred genes and confirmed the preferred expression patterns in plants using the GUS reporting system. Furthermore, cis-regulatory element analysis revealed that pollen specific elements such as POLLEN1LELAT52, and 5659BOXLELAT5659 were commonly identified in the promoter regions of eight rice genes with more frequency than estimation. Our study will provide new sights on early pollen development in rice, a model crop plant.

Bioinformatics resources for pollen

Bioinformatics for Pollen. Pollen plays a key role in crop production, and its development is the most delicate phase in reproduction. Different metabolic pathways are involved in pollen development, and changes in the level of some metabolites, as well as responses to stress, are correlated with the reduction in pollen viability, leading consequently to a decrease in the fruit production. However, studies on pollen may be hard because gamete development and fertilization are complex processes that occur during a short window of time. The rise of the so-called -omics sciences provided key strategies to promote molecular research in pollen tissues, starting from model organisms and moving to increasing number of species. An integrated multi-level approach based on investigations from genomics, transcriptomics, proteomics and metabolomics appears now feasible to clarify key molecular processes in pollen development and viability. To this aim, bioinformatics has a fundamental role for data production and analysis, contributing varied and ad hoc methodologies, endowed with different sensitivity and specificity, necessary for extracting added-value information from the large amount of molecular data achievable. Bioinformatics is also essential for data management, organization, distribution and integration in suitable resources. This is necessary to catch the biological features of the pollen tissues and to design effective approaches to identifying structural or functional properties, enabling the modeling of the major involved processes in normal or in stress conditions. In this review, we provide an overview of the available bioinformatics resources for pollen, ranging from raw data collections to complete databases or platforms, when available, which include data and/or results from -omics efforts on the male gametophyte. Perspectives in the fields will also be described.

Identification of cis-elements and evaluation of upstream regulatory region of a rice anther-specific gene, OSIPP3, conferring pollen-specific expression in Oryza sativa (L.) ssp. indica

Pollen-specific expression. Promoters comprise of various cis-regulatory elements which control development and physiology of plants by regulating gene expression. To understand the promoter specificity and also identification of functional cis-acting elements, progressive 5' deletion analysis of the promoter fragments is widely used. We have evaluated the activity of regulatory elements of 5' promoter deletion sequences of anther-specific gene OSIPP3, viz. OSIPP3-∆1 (1504 bp), OSIPP3-∆2 (968 bp), OSIPP3-∆3 (388 bp) and OSIPP3-∆4 (286 bp) through the expression of transgene GUS in rice. In silico analysis of 1504-bp sequence harboring different copy number of cis-acting regulatory elements such as POLLENLELAT52, GTGANTG10, enhancer element of LAT52 and LAT56 indicated that they were essential for high level of expression in pollen. Histochemical GUS analysis of the transgenic plants revealed that 1504- and 968-bp fragments directed GUS expression in roots and anthers, while the 388- and 286-bp fragments restricted the GUS expression to only pollen, of which 388 bp conferred strong GUS expression. Further, GUS staining analysis of different panicle development stages (P1-P6) confirmed that the GUS gene was preferentially expressed only at P6 stage (late pollen stage). The qRT-PCR analysis of GUS transcript revealed 23-fold higher expression of GUS transcript in OSIPP3-Δ1 followed by OSIPP3-Δ2 (eightfold) and OSIPP3-Δ3 (threefold) when compared to OSIPP3-Δ4. Based on our results, we proposed that among the two smaller fragments, the 388-bp upstream regulatory region could be considered as a promising candidate for pollen-specific expression of agronomically important transgenes in rice.

Rice tissue-specific promoters and condition-dependent promoters for effective translational application

Rice (Oryza sativa) is one of the most important staple food crops for more than half of the world's population. The demand is increasing for food security because of population growth and environmental challenges triggered by climate changes. This scenario has led to more interest in developing crops with greater productivity and sustainability. The process of genetic transformation, a major tool for crop improvement, utilizes promoters as one of its key elements. Those promoters are generally divided into three types: constitutive, spatiotemporal, and condition-dependent. Transcriptional control of a constitutive promoter often leads to reduced plant growth, due to a negative effect of accumulated molecules during cellular functions or energy consumption. To maximize the effect of a transgene on transgenic plants, it is better to use condition-dependent or tissue-specific promoters. However, until now, those types have not been as widely applied in crop biotechnology. In this review, we introduce and discuss four groups of tissue-specific promoters (50 promoters in total) and six groups of condition-dependent promoters (27 promoters). These promoters can be utilized to fine-tune desirable agronomic traits and develop crops with tolerance to various stresses, enhanced nutritional value, and advanced productivity.

A decade of pollen transcriptomics

KEY MESSAGE

Overview of pollen transcriptome studies. Pollen development is driven by gene expression, and knowledge of the molecular events underlying this process has undergone a quantum leap in the last decade through studies of the transcriptome. Here, we outline historical evidence for male haploid gene expression and review the wealth of pollen transcriptome data now available. Knowledge of the transcriptional capacity of pollen has progressed from genetic studies to the direct analysis of RNA and from gene-by-gene studies to analyses on a genomic scale. Microarray and/or RNA-seq data can now be accessed for all phases and cell types of developing pollen encompassing 10 different angiosperms. These growing resources have accelerated research and will undoubtedly inspire new directions and the application of system-based research into the mechanisms that govern the development, function and evolution of angiosperm pollen.

A novel binary T-vector with the GFP reporter gene for promoter characterization

Several strategies have been developed to clone PCR fragments into desired vectors. However, most of commercially available T-vectors are not binary vectors and cannot be directly used for Agrobacterium-mediated plant genetic transformation. In this study, a novel binary T-vector was constructed by integrating two AhdI restriction sites into the backbone vector pCAMBIA 1300. The T-vector also contains a GFP reporter gene and thus, can be used to analyze promoter activity by monitoring the reporter gene. On the other hand, identification and characterization of various promoters not only benefit the functional annotation of their genes but also provide alternative candidates to be used to drive interesting genes for plant genetic improvement by transgenesis. More than 1,000 putative pollen-specific rice genes have been identified in a genome-wide level. Among them, 67 highly expressed genes were further characterized. One of the pollen-specific genes LOC_Os10g35930 was further surveyed in its expression patterns with more details by quantitative real-time reverse-transcription PCR (qRT-PCR) analysis. Finally, its promoter activity was further investigated by analyzing transgenic rice plants carrying the promoter::GFP cassette, which was constructed from the newly developed T-vector. The reporter GFP gene expression in these transgenic plants showed that the promoter was active only in mature but not in germinated pollens.

Transcriptional silencing of heterologous anther promoters in maize: a genetic method to replace detasseling for seed production

The promoter of the maize male fertility gene ZmMs45, and other anther-specific maize promoters, was previously shown to be transcriptionally silenced by constitutively expressed promoter-inverted repeat RNAs (pIRs). In addition, ZmMS45pIR-mediated male sterility was reversed by co-expression of Ms45 transcribed by promoters not targeted by pIR RNA silencing. In this report, male fertility was restored to ms45 maize by fusing non-maize inflorescence promoters to the ZmMS45 coding region. This complementation assay also established that these rice or Arabidopsis promoters, when expressed as pIRs, functioned to silence sequence identical promoters. These observations were exploited to develop a genetic method to replace maize detasseling during hybrid seed production. In this system, the ZmMS45 coding region was fused to one of two dissimilar non-maize promoters to generate paired sets of ms45 recessive inbred parents which could be self-pollinated and maintained independently. Linked to each unique Ms45 gene was a non-maize pIR which targeted the promoter transcribing the Ms45 copy contained in the paired inbred parent plant. A cross of these pairs brings the dissimilar pIR cassettes together and resulted in silencing both transformed copies of Ms45. The net result uncovers the ms45 allele carried by the inbreds yielding male sterile progeny. The application of heterologous promoters and transcriptional silencing in plants provides an alternative to post-transcriptional gene silencing as a means to restore and silence gene function in plants.