Floral Meristem And Floral Organ Development Pdf
File Name: floral meristem and floral organ development .zip
Advances in Botanical Research publishes in-depth and up-to-date reviews on a wide range of topics in plant sciences. Currently in its 72nd volume, the series features several reviews by recognized experts on all aspects of plant genetics, biochemistry, cell biology, molecular biology, physiology and ecology. This thematic volume features reviews on the molecular genetics of floral transition and flower development.
- Analyzing Floral Meristem Development
- Associated Content
- The Molecular Genetics of Floral Transition and Flower Development, Volume 72
Analyzing Floral Meristem Development
Floral transition, the onset of plant reproduction, involves changes in shape and identity of the shoot apical meristem SAM. The change in shape, termed doming, occurs early during floral transition when it is induced by environmental cues such as changes in day-length, but how it is regulated at the cellular level is unknown.
We defined the morphological and cellular features of the SAM during floral transition of Arabidopsis thaliana. Both cell number and size increased during doming, and these changes were partially controlled by the gene regulatory network GRN that triggers flowering.
Furthermore, dynamic modulation of expression of gibberellin GA biosynthesis and catabolism enzymes at the SAM contributed to doming. Expression of these enzymes was regulated by two MADS-domain transcription factors implicated in flowering. We provide a temporal and spatial framework for integrating the flowering GRN with cellular changes at the SAM and highlight the role of local regulation of GA. In plants, all shoot tissues are derived from the shoot apical meristem SAM , a group of cells at the apex of the plant that includes a population of self-renewing stem cells.
Organ primordia are formed continuously on the flanks of the SAM, and these change in identity during growth and development. In the model plant Arabidopsis thaliana , leaf primordia are formed during vegetative growth, but at floral transition the developmental identity of the SAM changes to an inflorescence meristem, and it initiates the formation of floral primordia.
This process of floral induction represents the first step in plant reproduction and is closely regulated by environmental cues and by the developmental stage of the plant. For example, floral induction of A.
Here we define early cellular changes at the SAM during floral induction in response to LDs, and determine the contributions of genes that control flowering time or encode enzymes that regulate levels of the phytohormone gibberellin GA. The size and shape of the inflorescence meristem, and the regulation of cell division and cell size within it, have been studied in detail Gaillochet et al.
However, the programmed alterations in shape of the SAM that occur during the transition from a vegetative to inflorescence meristem are less well understood.
During induction of flowering in many plant species, the SAM increases in size and takes on a domed shape prior to the production of flowers, and these changes are induced by exposure to environmental cues Kwiatkowska, The contribution of different regions of the meristem to doming has been analyzed. Cells in the CZ divide slowly, whereas cells in the PZ divide more frequently to produce organ primordia. Similar conclusions were drawn from classical histological studies in Sinapis alba and Helianthus annuus , where increases in mitotic activity at the SAM upon floral induction reduced the difference in the rate of mitosis between the CZ and the PZ Bodson, ; Marc and Palmer, Although these histological analyses identified the correlation between cell division frequency and enlargement of the SAM, the resulting cellular changes and the molecular mechanisms that underlie the phenomenon have not been determined.
However, the contribution at the cellular level of florigen to doming of the SAM during floral transition remains to be determined. Genetic analyses have defined a pathway that regulates flowering of A. On the other hand, flowering of A. The histological and transcriptional profiles of the SAM change dramatically as flowering is initiated and proceeds, but the mechanisms underlying how these histological changes occur and are initiated by environmental cues remain largely unknown Kwiatkowska, ; Laufs et al.
GA promotes diverse biological processes, including cell elongation, cell division, and floral induction Yamaguchi, The strongly GA-deficient ga mutant of A.
Corresponding to this phenotype, the level of bioactive GA 4 increases strongly in shoot apices under SDs around the time of floral induction Eriksson et al. Both are encoded by gene families in A. Transcription of GA biosynthesis and deactivating genes is regulated by DELLA proteins, demonstrating that these contribute to feedback and feedforward regulation of GA metabolism Hedden and Phillips, ; Zentella et al.
GA levels are strongly repressed in the SAM of different plant species during vegetative development. Therefore, the concentration of GA is maintained at a low level in the SAM and this is proposed to be required for meristem activity. Here we analyze SAM shape and cellular content by confocal microscopy and demonstrate dynamic histological and cellular changes at the SAM during floral transition induced by LDs.
Both the number and size of the cells in the SAM increased in the early stages of this process, and these changes are at least partially regulated by the photoperiodic flowering pathway and GA. Detailed observations of reporter lines revealed dynamic changes in expression patterns of genes encoding GA biosynthesis and catabolism enzymes in the SAM.
Furthermore, the expression of these genes was found to be regulated by two MADS-domain transcription factors that play key roles in the control of flowering time.
These results define roles for the photoperiodic flowering and phytohormone signaling pathways in the dynamic control of SAM properties during floral transition. For this analysis, the SAM was defined as the region between the first developing primordia P n and its boundaries were delimited by regions of negative Gaussian curvature Figure 1—figure supplement 2A.
In particular, a dramatic increase in the number of cells in the SAM was observed between 3 and 5 days after transfer to LDs Figure 1F. Therefore, we next examined the size of the cells in the SAM during floral transition. Cell size increased in response to LDs in both regions, but the effect was stronger in the outer ring area than in the central region Figure 1—figure supplement 2B.
These histological analyses suggest that as well as cell number, cell size increased in response to transfer from SDs to LDs and that the transient enlargement of the cells correlates with doming of the SAM during floral transition.
We next examined whether increases in the number and size of the cells in the SAM are associated with floral induction and activity of the photoperiodic flowering pathway. To this end, we analyzed the meristem of the ft tsf-1 mutant, in which flowering is not induced in response to LDs.
Besides a small increase in cell size observed at seven LDs, no transient increase in cell size was observed in the ft tsf-1 mutant at five LDs Figure 1G. Consistent with this observation, doming of the SAM was strongly delayed in this background, although the area of the SAM expanded laterally after transfer to LDs Figure 1—figure supplement 1A. Previous studies showed that GA regulates both cell division and elongation in the root apical meristem Achard et al.
This transgene reduces the level of GA precursor specifically in the SAM, but is not expressed directly in the epidermis Lincoln et al. However, the meristem of the KNATGA2ox7 line was morphologically different from that of the ft tsf-1 mutant, with a specific reduction in meristem width Figure 1—figure supplement 1A,D, and E.
In addition, cell area in the meristematic region of this line was larger than for the ft tsf-1 mutant after five LDs Figure 1G. Taken together, our analyses suggest that the increase in cell number and cell size at the SAM during floral induction induced by LDs is mediated by both the photoperiodic flowering pathway and GA signals, and these appear to act at least partially through different mechanisms.
However, the detailed spatiotemporal expression pattern of GA20ox2 has not been analyzed. The transgene was introduced into the ga20ox2 —1 mutant and complemented its late-flowering phenotype under SDs Figure 2—figure supplement 1I. The cell walls were stained with Renaissance magenta. Gaussian curvature left panel , VENUS signal intensity middle panel , and cell area right panel were extracted. The positions of future primordia i n were predicted from those of existing primordia P n.
GA20ox2 transcription is downregulated by excessive amounts of GA via a feedback mechanism Rieu et al. The signal was weakly detected only in the abaxial side of leaf primordia up to 5wSD, but was hardly detectable from 6wSD, when floral primordia are produced instead of leaf primordia Figure 2—figure supplement 3A.
We compared meristem size in ga20ox2 —1 and Col However, in the 5LD samples, the meristem area was smaller in ga20ox2 —1 compared with Col-0 Figure 3B.
Analysis of different regions of the meristem, as described previously in Figure 1—figure supplement 2 , at 5LD detected a reduced number of cells and the presence of smaller cells in the ring outside the central region Figure 3B—F.
This suggests that activity of GA20ox2 contributes to the increase in cell size in the PZ at 5LD during floral transition, but the overall effect of ga20ox2 —1 on meristematic cell size is weaker than that of KNAT1:GA2ox7 Figures 1G and 3D , indicating that other enzymes might also participate in increasing GA level at this stage.
To examine the contribution of GA2 oxidases in flowering under LDs, we scored the number of leaves produced before flowering under those conditions. Although the contribution of GA to flowering under LDs was smaller than under SDs, the quintuple mutant in which all five C 19 - GA2ox genes are mutated ga2ox1 —1, ga2ox2 —1, ga2ox3—1, ga2ox4 —1, and ga2ox6 —2 flowered with significantly fewer rosette leaves than wild-type plants under LDs Figure 4—figure supplement 1A—C.
Notably, the ga2ox2—1 ga2ox4—1 ga2ox6 —2 triple mutant and ga2ox4 —1 single mutant flowered as early as the ga2ox quintuple mutant Figure 4—figure supplement 1A—C , suggesting that GA2ox4 is the major enzyme in this class that delays flowering time under LDs.
Thus, ela1 mutants produced cauline leaves on the inflorescence stem at nodes that produce flowers in wild-type plants. To examine whether C 19 -GA2ox enzymes are involved in flower formation, we counted the number of cauline leaves produced on the inflorescence stem of ga2ox mutants.
The number of cauline leaves was indistinguishable in ga2ox mutants and wild-type plants Figure 4—figure supplement 1D , suggesting that C 19 -GA2ox enzymes increase the duration of vegetative development prior to shoot elongation, but are not involved in regulating the transition from cauline leaves to floral primordia after bolting.
Next, we examined the expression of GA2ox genes in shoot apices. GA2ox2 and GA2ox4 are expressed in shoot apices Jasinski et al. A previous study showed that GA2ox4 transcript level is upregulated by GA treatment of wild-type seedlings via a feedforward mechanism Rieu et al.
These observations suggest that the feedforward regulation of GA2ox4 by GA is active in the SAM during the vegetative stage but is blocked during floral transition.
Cell walls were stained with Renaissance magenta. The signal intensity was significantly weaker between 4wSD and 5wSD Figure 4—figure supplement 5A , when the floral transition occurs under these conditions Hyun et al. In the reproductive stage 6 and 7wSD , the strong signal was detected again in the floral primordia Figure 4—figure supplement 5A.
These observations suggest that the expression of GA2ox4 changes dynamically depending on the developmental stage of the floral transition, even under SDs. This result again confirmed the tight correlation between GA2ox4 downregulation and the floral transition.
Furthermore, after transfer of 2wSD-grown plants to LDs, the size of the meristem and the cell number in the SAM of ga2ox4 —3 were indistinguishable from those of wild-type Col-0 Figure 4—figure supplement 6A—C , consistent with GA2ox4 expression being reduced in Col-0 plants under these conditions. Nevertheless, a significant difference in cell area was observed between Col-0 and ga2ox4 —3 SAMs after exposure to 5 LDs, with the cells of ga2ox4 —3 being slightly larger than those of Col-0 Figure 4—figure supplement 6D.
A previous study demonstrated that reduced GA levels in young floral primordia allow RGA to accumulate and interact with SPL proteins to promote AP1 transcription and confer floral identity Yamaguchi et al. To examine whether GA2ox4 may contribute to reducing GA levels during the acquisition of floral identity, we compared its spatial expression pattern with that of AP1 during floral transition and in the mature inflorescence Figure 5.
This observation suggests that GA2ox4 contributes to the reduction in GA levels in the floral primordia of the mature inflorescence. This observation was consistent with our phenotyping analysis, which showed that the number of cauline leaves did not increase in ga2ox4 mutants, suggesting that acquisition of floral meristem identity was not impaired Figure 4—figure supplement 1D.
The AP1-GFP signal was occasionally detected in developed leaf primordia prior to its expression in floral primordia, which is probably due to the AP1 promoter activity, as reported previously Hempel et al. Maximum intensity projections A—D and longitudinal sections are shown. The dynamic expression patterns of GA20ox2 and GA2ox4 tightly correlated with exposure to LDs and the developmental stage of the plants.
Therefore, we examined the involvement of photoperiodic flowering pathway genes on the expression patterns of GA20ox2 and GA2ox4.
However, the expression of GA20ox2 under inductive LDs has not been examined. The level of GA20ox2 transcript was not affected in the ft tsf-1 mutant background, but was greatly elevated in svp mutant apices compared to Col-0 at 9 and 11 days after germination Figure 6A and Figure 6—figure supplement 1A.
GA20ox2 transcript level was higher in soc mutants than in Col-0 at later time points Figure 6B. All samples were harvested 8 hr after dawn. E—G Genetic interaction tests between mutants of GA metabolism genes and soc1. Original data of leaf number of different genotypes for Figure 6E—G. We also used MorphoGraphX to analyze the morphology of the shoot meristem of soc mutants during the floral transition to compare this with the previous analysis of ga20ox2 —1 and ga2ox4 —3 mutants Figure 3 and Figure 4—figure supplement 6.
This result is consistent with the late-flowering phenotype of the soc mutant and suggests that the SAM of soc mutant domes to the same extent as Col-0, but that the process is more gradual and extends over 2 days longer. This result is in contrast to that observed for ft tsf mutants, which did not form a domed meristem throughout the time course Figure 1.
Original data of cell size of each genotype for Figure 7D. We then examined the effect of the ga20ox2 mutation on the flowering time of soc1 mutants. The synergistic effect of ga20ox2 on soc1 is not simply caused by the general growth defect of GA deficiency, because mutation in another GA biosynthesis enzyme gene, GA3ox1 , had only a minor effect on soc1 flowering time Figure 6E—G.
We also examined the effect of genes in the photoperiodic flowering pathway on the mRNA level of GA2ox4.
The fon1 mutants exhibit normal vegetative development and produce normal inflorescence meristems and immature flowers before stage 6. The fon1 floral meristem functions longer than does that of the wild type: after the outer three-whorl organ primordia have initiated, the remaining central floral meristem continues to produce additional stamen primordia interior to the third whorl. Prolonged fon1 floral meristem activity also results in an increased number of carpels. The clavata clv mutations are known to affect floral meristem activity. We have analyzed the clv1 fon1, clv2 fon1, and clv3 fon1 double mutants. These double mutants all have similar phenotypes, with more stamens and carpels than either fon1 or clv single mutants. This indicates that FON1 and CLV genes function in different pathways to control the number of third- and fourth-whorl floral organs.
PDF | Flowers contain the male and female sexual organs that are critical for plant reproduction and survival. Each individual flower is.
The Molecular Genetics of Floral Transition and Flower Development, Volume 72
Protocol DOI: Flowers contain the male and female sexual organs that are critical for plant reproduction and survival. Each individual flower is produced from a floral meristem that arises on the flank of the shoot apical meristem and consists of four organ types:. Each individual flower is produced from a floral meristem that arises on the flank of the shoot apical meristem and consists of four organ types: sepals, petals, stamens, and carpels. Because floral meristems contain a transient stem-cell pool that generates a small number of organs composed of a limited number of cell types, they are excellent model systems for studying stem-cell maintenance and termination, cell fate specification, organ morphogenesis, and pattern formation. Arabidopsis thaliana. Floral meristem, organ number.
Floral transition, the onset of plant reproduction, involves changes in shape and identity of the shoot apical meristem SAM. The change in shape, termed doming, occurs early during floral transition when it is induced by environmental cues such as changes in day-length, but how it is regulated at the cellular level is unknown. We defined the morphological and cellular features of the SAM during floral transition of Arabidopsis thaliana. Both cell number and size increased during doming, and these changes were partially controlled by the gene regulatory network GRN that triggers flowering. Furthermore, dynamic modulation of expression of gibberellin GA biosynthesis and catabolism enzymes at the SAM contributed to doming.
Metrics details. Flower development directly affects fruit production in tomato. Despite the framework mediated by ABC genes have been established in Arabidopsis, the spatiotemporal precision of floral development in tomato has not been well examined.
- Неверный ключ. Все застыли в ужасе. На экране перед ними высветилось сообщение об ошибке: НЕДОПУСТИМЫЙ ВВОД. ТОЛЬКО В ЦИФРОВОЙ ФОРМЕ - Черт его дери! - взорвался Джабба.
Однако Стратмор ничего не объяснил, а Беккер не решился спросить. АНБ, - подумал. - НБ - это, конечно, не болтай. Вот такое агентство. На другой стороне авениды Изабеллы он сразу же увидел клинику с изображенным на крыше обычным красным крестом на белом поле.
- Ты думаешь, что в ТРАНСТЕКСТ проник вирус. Мидж вздохнула: - А что еще это может. - Это может быть не вашим делом! - раздался зычный голос у них за спиной. Мидж от неожиданности стукнулась головой о стекло. Бринкерхофф опрокинул директорский стул и бросился к двери.
Банк данных АНБ был сконструирован таким образом, чтобы никогда не оставался без электропитания - в результате случайности или злого умысла. Многоуровневая защита силовых и телефонных кабелей была спрятана глубоко под землей в стальных контейнерах, а питание от главного комплекса АНБ было дополнено многочисленными линиями электропитания, независимыми от городской системы снабжения. Поэтому отключение представляло собой сложную серию подтверждений и протоколов, гораздо более сложную, чем запуск ядерной ракеты с подводной лодки. - У нас есть время, но только если мы поспешим, - сказал Джабба. - Отключение вручную займет минут тридцать.
Он попробовал встать, но настолько выбился из сил, что не смог ступить ни шагу и долго сидел, изможденный вконец, на каменных ступеньках, рассеянно разглядывая распростертое у его ног тело. Глаза Халохота закатились, глядя в пустоту. Странно, но его очки ничуть не пострадали.
В Штатах. - А связаться с ними пробовала. - Пустой номер. Наверное, уплыли на уик-энд с друзьями на яхте.
Иди за мной! - сказал. И направился в сторону люка. - Коммандер. Хейл очень опасен. Он… Но Стратмор растворился в темноте.