雌雄異株植物ヒロハノマンテマにおける両性花変異体とBクラス遺伝子SlAP3X/Y欠失変異体の雌雄異株性に関する研究

学位の種別:課程博士University of Tokyo(東京大学

Narrowing Down the Mapping of Plant Sex-Determination Regions Using New Y-Chromosome-Specific Markers and Heavy-Ion Beam Irradiation-Induced Y-Deletion Mutants in Silene latifolia

Silene latifolia is a well-studied model system for plant XY sex determination. Three maleness factors are thought to function on the Y chromosome, gynoecium suppression factor (GSF), stamen-promoting factor (SPF), and male fertility factor (MFF), and their deletions result in hermaphrodites, anther defects, and pollen defects, respectively. Although a framework map of the Y chromosome exists, the sex determination genes have not been identified, and no markers close enough to potentially be used for BAC library screening are yet available. The analysis of Y deletion mutants by Y-chromosome-specific STS markers is an efficient way to isolate sex determination regions, but more Y-specific STS markers are needed to accelerate the exploration of sex determination factors. Herein, we report a marker design method that uses simple sequence repeats, which is especially effective on the Y chromosome of S. latifolia because it contains many simple sequence repeats. Six new Y-chromosome-specific STS markers were obtained, SmicSy1–6. These were used to detect relatively small Y deletion sites in heavy-ion beam irradiation-induced mutants. The mapping of male sex determination regions was narrowed down by using more markers and smaller-sized Y deletion mutants. One new marker, SmicSy6, is a proximal marker to SPF and, thus, a second index for SPF. The region including SPF is thought to be located between two SPF proximal markers. The flower phenotype correlates with the deletion size of SPF using SPF proximal markers. These findings represent new progress in isolating the sex determination factor, which has been studied for more than 50 years

Male/Female Trade-Off in Hermaphroditic Y-Chromosome Deletion Mutants of the Dioecious Plant Silene latifolia

The evolution of dioecy from hermaphroditism allows for avoidance of self-pollination, and its evolutionary background has been investigated both experimentally and theoretically since it was first proposed by Darwin. To reproduce this evolution, we screened hermaphroditic mutants of Silene latifolia using heavy-ion beam or γ-ray irradiation and characterized the phenotypes of their floral organs. Our scatterplots indicate severe deviations from the trade-off relationships between pollen and ovule numbers and between seed and germinated pollen numbers in hermaphroditic mutant S. latifolia. These deviations presumably led to promotion of dioecy from the ancestral state of S. latifolia. To infer the likely flower phenotypic characteristics of the ancestral plant of S. latifolia before evolving dioecy, the flowers of Silene viscosa, a naturally hermaphroditic plant related to S. latifolia were also characterized. S. viscosa exhibits both spatial separation of stamens from pistils within the flower (reverse herkogamy) and temporal separation of stamen and pistil maturation (dichogamy), raising the question of whether hermaphroditic mutant S. latifolia, which is thought to be the ancestral state, would possess these functions. We show that two hermaphroditic mutants of the dioecious plant S. latifolia exhibit signs of protogyny (reverse dichogamy) and approach herkogamy, as pistils were constantly longer than stamens. These findings illustrate the evolution of dioecy from hermaphroditism as a self-pollination avoidance mechanism and to balance the investments into male and female functions

Current status of cardiac resynchronization therapy device optimization in Japan

Background: Cardiac resynchronization therapy (CRT) is known to be effective for patients with heart failure. However, despite data suggesting that routine atrioventricular (AV) and interventricular (VV) delay optimization may play significant roles in CRT, there is no standard on how and when the CRT device should be optimized. The aim of this study was to characterize the current practice of CRT optimization in Japan. Methods: A survey was conducted to collect information on the procedural aspects of AV and VV delay optimization. The key survey items concerned what method is used for optimization, when optimization is performed, and what factors limit repetitive optimization. Results: Fifty-two physicians participated in the survey. Echocardiography was the chosen method for assessing AV and VV delays by 79.6% and 65.3% of physicians, respectively, and routine optimization was performed by 28.3%. The majority optimized the settings only once at pre-hospital discharge or on an “as-needed” basis. The factors limiting repeated optimization were the lack of available time (71.2%), qualified staff (53.8%), and reliable methods (55.8%). Conclusions: Repetitive CRT optimization is infrequently performed in Japan. Lack of time, human resource, and reliable methods were the major factors affecting the number of routine CRT optimization