In the Brassicaceae, intraspecific non-self pollen (compatible pollen) can germinate and grow into stigmatic papilla cells, while self-pollen or interspecific pollen is rejected at this stage. However, the mechanisms underlying this selective acceptance of compatible pollen remain unclear. Here, using a cell-impermeant calcium indicator, we showed that the compatible pollen coat contains signaling molecules that stimulate Ca(2+) export from the papilla cells. Transcriptome analyses of stigmas suggested that autoinhibited Ca(2+)-ATPase13 (ACA13) was induced after both compatible pollination and compatible pollen coat treatment. A complementation test using a yeast Saccharomyces cerevisiae strain lacking major Ca(2+) transport systems suggested that ACA13 indeed functions as an autoinhibited Ca(2+) transporter. ACA13 transcription increased in papilla cells and in transmitting tracts after pollination. ACA13 protein localized to the plasma membrane and to vesicles near the Golgi body and accumulated at the pollen tube penetration site after pollination. The stigma of a T-DNA insertion line of ACA13 exhibited reduced Ca(2+) export, as well as defects in compatible pollen germination and seed production. These findings suggest that stigmatic ACA13 functions in the export of Ca(2+) to the compatible pollen tube, which promotes successful fertilization.
Summary The root system is a crucial determinant of plant growth potential because of its important functions, e.g. uptake of water and nutrients, structural support and interaction with symbiotic organisms. Elucidating the molecular mechanism of root development and functions is therefore necessary for improving plant productivity, particularly for crop plants, including rice ( Oryza sativa ). As an initial step towards developing a comprehensive understanding of the root system, we performed a large‐scale transcriptome analysis of the rice root via a combined laser microdissection and microarray approach. The crown root was divided into eight developmental stages along the longitudinal axis and three radial tissue types at two different developmental stages, namely: epidermis, exodermis and sclerenchyma; cortex; and endodermis, pericycle and stele. We analyzed a total of 38 microarray data and identified 22 297 genes corresponding to 17 010 loci that showed sufficient signal intensity as well as developmental‐ and tissue type‐specific transcriptome signatures. Moreover, we clarified gene networks associated with root cap function and lateral root formation, and further revealed antagonistic and synergistic interactions of phytohormones such as auxin, cytokinin, brassinosteroids and ethylene, based on the expression pattern of genes related to phytohormone biosynthesis and signaling. Expression profiling of transporter genes defined not only major sites for uptake and transport of water and nutrients, but also distinct signatures of the radial transport system from the rhizosphere to the xylem vessel for each nutrient. All data can be accessed from our gene expression profile database, RiceXPro ( http://ricexpro.dna.affrc.go.jp ), thereby providing useful information for understanding the molecular mechanisms involved in root system development of crop plants.
To evaluate growth and develop a growth model of the medicinal plant Angelica acutiloba, we grew plants of one cultivar in one nursery at nine sites in Honshu and Shikoku, Japan, from 2016 to 2018. The collected data thus reflect differences in growing environment. The model estimates root dry weight and root head diameter from the number of days at the preferred growing temperature range between lower and upper limits based on the daily mean air temperature, and incorporates growth suppression by high temperatures in summer 2018. It was used to develop a program for estimating the optimum harvest date at any location in Honshu and Shikoku from Agro-Meteorological Grid Square Data of NARO.
Summary Pollen has an extraordinary ability to convert from a dry state to an extremely rapidly growing state. During pollination, pollen receives water and Ca 2+ from the contacting pistil, which will be a directional cue for pollen tube germination. The subsequent rapid activation of directional vesicular transport must support the pollen tube growth, but the molecular mechanism leading to this process is largely unknown. We established a luciferase‐based pollination assay to screen genetic mutants defective in the early stage after pollination. We identified a plant‐specific VPS13, Arabidopsis thaliana VPS13a as important for pollen germination, and studied its molecular function. AtVPS13a mutation severely affected pollen germination and lipid droplet discharge from the rough endoplasmic reticulum. Cellular accumulation patterns of AtVPS13a and a secretory vesicle marker were synchronized at the polarized site, with a slight delay to the local Ca 2+ elevation. We found a brief Ca 2+ spike after initiation of pollen hydration, which may be related to the directional cues for pollen tube emergence. Although this Ca 2+ dynamics after pollination was unaffected by the absence of AtVPS13a, the mutant suffered reduced cell wall deposition during pollen germination. AtVPS13a mediates pollen polarization, by regulating proper directional vesicular transport following Ca 2+ signaling for directional tube outgrowth.
We applied the full-length cDNA overexpressor (FOX) gene-hunting system for systematic and genome-wide functional analysis of rice genes. In this study, we constructed a novel binary vector carrying the Gateway site-specific recombination cassette and then constructed rice FOX libraries containing a maximum of 13,823 independent, full-length cDNAs (fl-cDNAs) that correspond to approximately half the total number of rice fl-cDNA clones. By introducing the FOX libraries via Agrobacterium, we generated 2,586 FOX-rice lines exhibiting various visible alterations (e.g., plant height, tillers, leaves, and heading dates). The introduced fl-cDNAs, integrated into individual transgenic rice genomes, were amplified by genomic PCR and identified using sequencing analysis. The fl-cDNAs were PCR-amplified in 2,251 (94.2%) of the 2,389 FOX-rice lines that were examined, identifying 1,920 independent fl-cDNAs in the FOX lines. In addition to the previously generated FOX-rice plants, our new collection of FOX-rice lines produced through the Gateway system should be a useful tool for the efficient identification of gene functions in rice. Moreover, this Gateway-based technology should be applicable to other species in which a collection of fl-cDNA clones is available.
