Map-based cloning is a basic method for identifying the mutated gene in plants. We selected the gametophytic mutant, named as AP-26-09, in activation-tagging pool. Mutant plant showed various kinds of pollen phenotype, such as the different number of nucleus or abnormal shapes. For the map-based gene cloning, we conducted phenotypic analysis of F2 mapping population through the screening of DAPI-stained pollen using fluorescence microscopy. Genomic DNA of F2 plants is prepared from leaves of approximately 1000 plants. In order to define chromosomal region where mutation is located, we designed SSLP markers and performed PCR amplification. In this study, we characterized gametophytic mutant and determined the chromosomal location using map-based approach.

We recently reported rice promoters that are active in late stages of pollen development. However, rice promoters that allow manipulation of gene expression at earlier stages of pollen development are still very limited to date. In this study, we have chosen 10 putative microspore promoters, OsMSP1 through OsMSP10, based on publicly available transcriptomic datasets in rice (Oryza sativa L.). Sequence analysis of these promoter regions revealed some cis regulatory elements involved in pollen-specific expression. We also examined promoter activities using the promoter-GUS reporter constructs in both transgenic rice and Arabidopsis. In rice, all of the 10 promoters directed GUS signals from the microspore stage throughout the all stages of pollen development. In addition, while GUS signals from 4 promoters, OsMSP2, OsMSP7, OsMSP9 and OsMSP10, seem to be expressed preferentially during pollen development, those from other six promoters were observed in vegetative tissues such as leaves, stems, and roots of seedlings. Similarly, in Arabidopsis, all of the 10 promoters directed GUS signals during pollen development. In detail, 8 promoters, OsMSP1 ~ OsMSP8 directed GUS signals from the microspore stage, whereas 2 promoters, OsMSP9 and OsMSP10, exhibited GUS signals from tricellular stage. Furthermore, seven promoters, except for OsMSP1, OsMSP2 and OsMSP10, showed GUS signals in shoot apical region or root tissues of seedlings. Furthermore, we verified microspore activity of four promoters, OsMSP1, OsMSP2, OsMSP3 and OsMSP6, by complementation analysis of the sidecar pollen (scp) mutant which displays microspore-specific defects. Currently, further analyses are underway for GUS expression of T2 generation in transgenic rice and scp complementation with remaining promoters.

To identify genes that play critical roles during male gametogenesis in Arabidopsis, we have isolated several pollen morphological mutants from a mutagenized seed pool generated with a T-DNA activation vector. In this study, we have focused on a mutant plant producing ~50% abnormal pollen grains including high levels of collapsed pollen at maturity. The pollen developmental analysis showed that the mutant pollen phenotype was first observed at tricellular stage. Interestingly, the mutation was only maintained as a heterozygote due to the severely reduced genetic transmission through both sexes. TAIL PCR analysis led to the identification of the responsible gene which encodes a conserved oligomeric golgi complex component-related protein (COGCC). RT-PCR analysis showed predominant expression of the gene in reproductive organs including developing spores. The gene identity was confirmed by the result that mutant plants harboring a T-DNA containing corresponding wild type gene produced less level of mutant pollen grains. Furthermore, confocal laser scanning microscopy using mature pollen expressing COGCC-RFP driven under the native promoter showed small punctate signals, which are likely to be from the Golgi complex. Further experiments for co-localization of the COGCC-RFP with the Golgi markers are underway.

In the course of map-based cloning, mutant genes are identified through linkage to specific region on genetic map. Here, we demonstrated gametophytic mutant line, named as AP-28-23, in which mutant gene was mapped on chromosome 2. Based on phenotypic analysis of mature pollen, mutant phenotype of AP-28-23 was classified into three classes, wild-type showing 2-4%, moderate 35-53% and severe type 97-100% on aberrant pollen frequencies, respectively. The severe type is completely sterilized with 100% unfertilized ovules. We also revealed that the transmission was reduced through male gametophyte in the AP-28-23 line. The transmission efficiency (TE) through the male gametophyte is only 0.67%, whereas in the female gametophyte is 89.87%.

Tissue-specific promoters are a very useful tool for manipulating gene expression in a target tissue or organ; however, their range of applications in other plant species has not been determined, to date. In this study, we identified two late pollen-specific rice promoters (ProOsLPS10 and ProOsLPS11) via meta-anatomical expression analysis. We then investigated the expression of both promoters in transgenic rice (a homologous system) and Arabidopsis (a heterologous system) using ProOsLPS10 or ProOsLPS11::GFP-GUS constructs. As predicted by microarray data, both promoters triggered strong GUS expression during the late stages of pollen development in rice, with no GUS signals detected in the examined microspores and sporophytic tissues. Interestingly, these promoters exhibited different GUS expression patterns in Arabidopsis. While in Arabidopsis, the OsLPS10 promoter conferred GUS expression at the uni- and bi-cellular macrospore stages, as well as at the shoot apical region during the seedling stage, the OsLPS11 promoter was not active in the pollen at any stage, or in the examined sporophytic tissues. Furthermore, by performing a complementation analysis using a sidecar pollen (scp) mutant that displays developmental defects at the microspore stage, we found evidence that OsLPS10, which can be an applied promoter expressed in Arabidopsis, is useful for directing gene expression in the early stages of pollen development. Our results indicate that the OsLPS10 and OsLPS11 promoters can drive the expression of target genes during the late stages of pollen development in rice, but not in Arabidopsis. Our results also emphasize the necessity of confirming the applicability of an established promoter to heterologous systems.

The correct development of male gametophytes (pollen grains) in flowering plants is essential for proliferate in gamete production. Here we have taken a map-based cloning approach using Arabidopsis male gametophytic mutant, named gemini pollen3 (gem3) to identify and characterize key gene that is expressed gametophytically for the completion of microgametogenesis focusing on genes which control cell division and cell fate determination. Previously reported gem1 and gem2 mutants with similar characteristics to gem3 that are disturbed at asymmetric division and cytokinesis at pollen mitosis I (PMI) in Arabidopsis. However, gem3 was mapped to a different genetic locus, and pollen developmental analysis revealed that gem3 exert an effect at meiosis and mitosis causing complete sterility. We also discovered that gem3 homozygous lines produce aberrant pollen grains, arising from incomplete cytokinesis during male meiosis with sporophytic phenotypes of twisted-shape leaves, large flowers. This mutation shows reduced genetic transmission of gem3 allele through male gametophyte. In previous results, the gem3 locus was confirmed by mapping to the region located on chromosome 5. To further confirm strong candidate gene, we performed sequencing and genetic complementation analysis. Currently, we are performing functional studies of the gem3 gene for the better understanding of molecular mechanisms that control asymmetric division at meiosis and mitosis during pollen development.

OsLPS is pollen specific gene that express at late stage of pollen development in rice. Based on microarray database, promoter region of two genes Os03g0106900 and Os03g0106500 were identified. The sequence of 2287bp and 2468bp upstream region of these genes were amplified and designated as OsLPS10 and OsLPS11. These promoters were fused with GUS-GFP reporter gene in a destination vector, pKGWFS7 and introduced into rice (Dongjin cultivar) and Arabidopsis (Col-0). The results of GUS assay showed different pattern of gene expression in pollen of rice and Arabidopsis. In Arabidopsis, the OsLPS10 gene strongly activated in young anther and not expressed in mature pollen. Pollen development analysis revealed GUS expression was detected at unicellular stage and strongest at the bicellular pollen developmental stage. No GUS signal was recorded in mature pollen. In case of OsLPS11, no GUS signal was detected in during pollen development of inflorescent. By contrast, in rice, the GUS expression pattern of OsLPS10 and OsLPS11 exhibited similar. GUS expression was first detectable in the anthers of spikelets at the bicellular stage and intensity increased in tricellular and mature pollen. The GUS signal was not detected in the anthers in unicellular microspores in both genes, OsLPS10 and OsLPS11. The results suggested that these genes were different activity in heterologous plant system, monocot and dicot. Complementation analysis and Cis-regulatory elements will be examined to illuminate the characteristic of these genes

Based on the results of microarray analysis we selected ten candidate genes that express in pollen at the early pollen developmental stage. By PCR amplification, the promoter region of these genes were amplified from rice genomic DNA (Nipponbare) and cloned into the destination pKGWFS7 vector via an entry vector, pDONR201. The characteristic of promoters were evaluated in Arabidopsis thaliana (Col-0) through GUS expression analysis. Fifty T2 plants respectively from each promoter were tested. Whole inflorescence of individual plant was stained with 1mM X-Gluc solution to observe tissue-specific GUS expression patterns. The results showed that all 10 promoters activated in pollen tissues. Among them six promoters expressed at the early developmental stage (unicellular) of pollen and the others expressed at both early (unicellular) and late pollen developmental stage (mature pollen). The results indicated that these promoters would be potential applicable for the studies of pollen function. Currently, we are performing these promoters analysis in rice transgenic plants as well as molecular characterization.

The THO/TREX complex mediates the transport of nascent mRNAs from the nucleus towards the cytoplasm in animals, and it has a role in small RNA-dependent processes in plants. Here we describe five mutant alleles of Arabidopsis thaliana THO2, whichencodes a core subunit of the plant THO/TREX complex. tho2 mutants present strong developmental defects resembling those in plants compromised in microRNA (miRNA) activity. In agreement, not only the levels of siRNAs, but also of mature miRNAs were reduced in tho2 mutants. As a consequence miRNA target mRNAs accumulated to higher levels than in wild type. Yeast two hybrid experiments showed that THO2 does not seem to interact with any of the known miRNA biogenesis components, implying a more indirect role of THOs in small RNA biogenesis. We also detected alterations in the splicing pattern of genes encoding Serine/Arginine-rich proteins in tho2 mutants, suggesting a previously unappreciated role of the THO/TREX complex in alternative splicing.

Arabidopsis Fused kinase TWO-IN-ONE (TIO) controls phragmoplast expansion and interacts with the Kinesin-12 subfamily proteins that anchor the plus ends of interdigitating microtubules (MTs) in the phragmoplast midzone. Previous analyses of loss-of-function mutants and RNA interference lines revealed that TIO positively controls both somatic and gametophytic cell cytokinesis, however, knowledge of the full spectrum of TIO functions during plant development remains incomplete. In order to further characterize TIO functions, we expressed TIO and a range of TIO variants under control of its own promoter in wild type Arabidopsis plants. We discovered that TIO-overexpressing transgenic lines produce enlarged pollen grains, arising from incomplete cytokinesis during male meiosis, and showed sporophytic abnormalities indicating polyploidy. These phenotypes arose independently in TIO variants that abolished either gametophytic function or the ability of TIO to interact with Kinesin-12 subfamily proteins. Interaction assays in yeast showed TIO to bind to AtNACK2/TETRASPORE and plants doubly homozygous for kinesin-12a and kinesin-12b knockout mutations to produce enlarged pollen grains. Our results show that TIO dominantly inhibits male meiotic cytokinesis in a dosage dependent manner that may involve direct binding to acomponent of the canonical NACK-PQR cytokinesis signaling pathway.