LEUNIG has multiple functions in gynoecium development in Arabidopsis

The Arabidopsis gene LEUNIG was previously found to regulate floral organ identity. In this work we describe gynoecial phenotypes of newly isolated strong leunig alleles, leunig-101, leunig-102, and leunig-103. Gynoecia of these strong leunig mutants are united only at the basal part, leaving four unfused parts at the apex. Among them two medial ones are styles capped with stigmas, and two lateral ones are protrusions from valves. The gynoecium with unfused apex in leunig arises as a unit from a basal meristematic zone, suggesting that LEUNIG is required for normal congenital gynoecium fusion. The epidermal cells on growing inner surfaces of leunig gynoecium failed to fuse after they contact each other, indicating that LEUNIG is essential for the proper postgenital fusion. The epidermal cells at the very distal portion of protruded valves mimic those on wild-type styles, and those valves occasionally also have stigma-like tissues, indicating that LEUNIG function is required for the valve identity determination. We have also analyzed clavata1-4 leunig-101, clavata2-1 lug-101, fruitfull-1 leunig-101, and pinoid-1 leunig-101 double mutants. clavata1-4 leunig-101 and clavata2-1 leunig-101 exhibited additive phenotypes of single mutants, suggesting that LEUNIG and CLAVATA genes function in different pathways. In contrast, FRUITFULL and PINOID genes interact with LEUNIG to regulate gynoecium development. genesis 26:42-54, 2000.     

Expression of the Arabidopsis floral homeotic gene AGAMOUS is restricted to specific cell types late in flower development.

Mutations in the AGAMOUS (AG) gene cause transformations in two adjacent whorls of the Arabidopsis flower. Petals develop in the third floral whorl rather than the normal stamens, and the cells that would normally develop into the fourth whorl gynoecium behave as if they constituted an ag flower primordium. Early in flower development, AG RNA is evenly distributed throughout third and fourth whorl organ primordia but is not present in the organ primordia of whorls one and two. In contrast to the early expression pattern, later in flower development, AG RNA is restricted to specific cell types within the stamens and carpels as cellular differentiation occurs in those organs. Ectopic AG expression patterns in flowers mutant for the floral homeotic gene APETELA2 (AP2), which regulates early AG expression, suggest that the late AG expression is not directly dependent on AP2 activity.     

Meristic variation in Potamogeton flowers

Flowers of Potamogeton normally have a completely tetramerous plan. Deviations from this norm occur quite commonly in the uppermost flowers of the inflorescence; these variations have been reported before and usually involve a reduction in number of parts. Cases have now been found where the gynoecium of all or many flowers differs from the normal tetracarpellate arrangement; some species regularly have fewer and others more than four carpels. The developmental bases of meristic variation have been explored and quantitative studies of gynoecia and developing gynoecia have been undertaken. The data are used to evaluate the control and correlation of floral development in Potamogeton in general, and in particular the relationship between the gynoecium and the rest of the flower. The developing flower passes through two successive phases of organ initiation: one in which the perianth and stamen primordia arise, and one in which the gynoecial primordia arise. There seems to be little developmental relationship between the two phases except phyllotactic continuity. During the perianth/stamen phase each stamen primordium arises directly above a perianth member, and the presence of a perianth member seems to be a prerequisite for initiation of the stamen. The perianth/stamen phase seems to be rather stable so that normally four perianth/stamen associations are initiated, except in flowers at the tip of the inflorescence. In the gynoecial phase the number of carpel primordia initiated seems to depend on the relative size of carpel primordia and floral apex, and on whether or not the floral apex continues to grow while initiating carpel primordia.     

TOUSLED kinase activity oscillates during the cell cycle and interacts with chromatin regulators

The TOUSLED (TSL)-like nuclear protein kinase family is highly conserved in plants and animals. tsl loss of function mutations cause pleiotropic defects in both leaf and flower development, and growth and initiation of floral organ primordia is abnormal, suggesting that basic cellular processes are affected. TSL is more highly expressed in exponentially growing Arabidopsis culture cells than in stationary, nondividing cells. While its expression remains constant throughout the cell cycle in dividing cells, TSL kinase activity is higher in enriched late G2/M-phase and G1-phase populations of Arabidopsis suspension culture cells compared to those in S-phase. tsl mutants also display an aberrant pattern and increased expression levels of the mitotic cyclin gene CycB1;1, suggesting that TSL represses CycB1;1 expression at certain times during development or that cells are delayed in mitosis. TSL interacts with and phosphorylates one of two Arabidopsis homologs of the nucleosome assembly/silencing protein Asf1 and histone H3, as in humans, and a novel plant SANT/myb-domain protein, TKI1, suggesting that TSL plays a role in chromatin metabolism.     

Floral organogenesis of Potamogeton distinctus A. Benn. (Potamogetonaceae)

The floral organogenesis of Potamogeton distinctus A. Benn. was observed under the scanning electron microscope (SEM). The floral buds are first initiated on the lower portion of inflorescence in alternating whorls of three. Each of the floral buds is subtended by a bract primordium during the early stages. The primordia of the floral appendages arise on the floral bud acropetally. Two lateral tepals are first initiated and then two median ones soon after. Stamens are normally initiated as elongate primordia opposite the tepals, with the two lateral stamens preceding the median ones. The two carpel primordia arise alternating with the stamens. In some flowers, one of the two gynoecial primordia becomes inactive soon after they are initiated, or only one carpel primordium is initiated. The present observation of the gynoecial development supports the viewpoint that the evolution of flower in Potamogeton involves a reduction in number of parts. The existence of bract primordium during the early stages in many species of Potamogeton indicates that the absence of bractin mature flowers should be the result of reduction.     

黄瓜离体子叶节花芽和营养芽分化中CFL基因的表达

CFL基因是从黄瓜中克隆到的拟南芥LEAFY(LFY)同源基因.以离体黄瓜子叶培养物成花为实验体系,利用mRNA原位杂交技术对CFL基因在花芽和营养芽分化过程中的时空表达进行了分析.结果如下:在花芽分化过程中,CFL基因在花原基形成、花器官原基分化及各轮花器官形成之初强表达,在花器官形成以后表达减弱或不表达;在营养芽分化过程中,CFL基因在分生组织、叶原基和幼叶中有明显表达,在成熟组织中不表达.结果说明CFL基因的表达在黄瓜子叶节花芽和营养芽分化中原基的分化形成是必需的.结果提示CFL基因可能参与细胞分裂调控和启动、营养性分生组织向花分生组织转变等过程.     

NO APICAL MERISTEM (MtNAM) regulates floral organ identity and lateral organ separation in Medicago truncatula

? The CUP-SHAPED COTYLEDON (CUC)/NO APICAL MERISTEM (NAM) family of genes control boundary formation and lateral organ separation, which is critical for proper leaf and flower patterning. However, most downstream targets of CUC/NAM genes remain unclear. ? In a forward screen of the tobacco retrotransposon1 (Tnt1) insertion population in Medicago truncatula, we isolated a weak allele of the no-apical-meristem mutant mtnam-2. Meanwhile, we regenerated a mature plant from the null allele mtnam-1. These materials allowed us to extensively characterize the function of MtNAM and its downstream genes. ? MtNAM is highly expressed in vegetative shoot buds and inflorescence apices, specifically at boundaries between the shoot apical meristem and leaf/flower primordia. Mature plants of the regenerated null allele and the weak allele display remarkable floral phenotypes: floral whorls and organ numbers are reduced and the floral organ identity is compromised. Microarray and quantitative RT-PCR analyses revealed that all classes of floral homeotic genes are down-regulated in mtnam mutants. Mutations in MtNAM also lead to fused cotyledons and leaflets of the compound leaf as well as a defective shoot apical meristem. ? Our results revealed that MtNAM shares the role of CUC/NAM family genes in lateral organ separation and compound leaf development, and is also required for floral organ identity and development.     

Negative regulation of the Arabidopsis homeotic gene AGAMOUS by the APETALA2 product.

We characterized the distribution of AGAMOUS (AG) RNA during early flower development in Arabidopsis. Mutations in this homeotic gene cause the transformation of stamens to petals in floral whorl 3 and of carpels to another ag flower in floral whorl 4. We found that AG RNA is present in the stamen and carpel primordia but is undetectable in sepal and petal primordia throughout early wild-type flower development, consistent with the mutant phenotype. We also analyzed the distribution of AG RNA in apetela2 (ap2) mutant flowers. AP2 is a floral homeotic gene that is necessary for the normal development of sepals and petals in floral whorls 1 and 2. In ap2 mutant flowers, AG RNA is present in the organ primordia of all floral whorls. These observations show that the expression patterns of the Arabidopsis floral homeotic genes are in part established by regulatory interactions between these genes.     

离体黄瓜子叶节花芽分化与内源激素及多胺的关系

用高效液相色谱法(HPLC)测定了黄瓜子叶节花芽分化期(0—6天)内源激素及多胺的变化。结果显示,子叶培养0—2天生长素(IAA)、赤霉素(GA3)、玉米素(ZT)、脱落酸(ABA)等4种内源激素均明显下降,4—5天略有上升,表明0-2天IAA、GA3和ABA的剧降有利于花原基形成,3—5天较高的ZT含量有利于花器官原基的形成。除腐胺(Put)外,精胺(Spm)、亚精胺(Spd)、尸胺(Cad)在0—1天均下降,1—4天上升,4—5天再下降,Put在0—1天急剧上升,而后持续下降,表明高水平的内源多胺总量和Put可能有利于花原基分化,2天后Spm含量上升有利于花器官原基分化,而Cad含量变化可能是区别花芽和营养芽分化的特征之一。     

离体黄瓜子叶节花芽分化与内源激素及多胺的关系

用高效液相色谱法(HPLC)测定了黄瓜子叶节花芽分化期(0-6天)内源激素及多胺的变化。结果显示,子叶培养0-2天生长素(IAA)、赤霉素(GA_3)、玉米素(ZT)、脱落酸(ABA)等4种内源激素均明显下降,4-5天略有上升,表明0-2天IAA、GA_3和ABA的剧降有利于花原基形成,3-5天较高的ZT含量有利于花器官原基的形成。除腐胺(Put)外,精胺(Spm)、亚精胺(Spd)、尸胺(Cad)在0-1天均下降,1-4天上升,4-5天再下降,Put在0-1天急剧上升,而后持续下降,表明高水平的内源多胺总量和Put可能有利于花原基分化,2天后Spm含量上升有利于花器官原基分化,而Cad含量变化可能是区别花芽和营养芽分化的特征之一。     

Expression of HtKNOT1, a class I KNOX gene, overlaps cell layers and development compartments of differentiating cells in stems and flowers of Helianthus tuberosus

In plant, post-embryonic development relies on the activities of indeterminate cell populations termed meristems, spatially clustered cell lineages, wherein a subset divides indeterminately. For correct growth, the plant must maintain a constant flow of cells through the meristem, where the input of dividing pluripotent cells offsets the output of differentiating cells. KNOTTED1-like homeobox (KNOX) genes are expressed in specific patterns in the plant meristems and play important roles in maintaining meristematic cell identity. We have analyzed the expression pattern of HtKNOT1, a class I KNOX gene of Helianthus tuberosus, in stems, inflorescence meristems, floral meristems and floral organs. HtKNOT1 is expressed in cambial cells, phloem cells and xylematic parenchyma within apical stem internodes, while in basal internodes HtKNOT1 expression was restricted to the presumptive initials and recently derived phloem cells. In the reproductive phase, HtKNOT1 mRNAs were detected in both the inflorescence and floral meristems as well within lateral organ primordia (i.e. floral bracts, petals, stamens and carpels). In more differentiated flowers, the expression of HtKNOT1 was restricted to developing ovules and pollen mother cells. HtKNOT1 may play a dual role being required to maintain the meristem initials as well as initiating differentiation and/or conferring new cell identity. In particular, it is possible that HtKNOT1 cooperates at floral level with additional factors that more specifically control floral organs and pollen development in H. tuberosus.