A Factor Linking Floral Organ Identity and Growth Revealed by Characterization of the Tomato Mutant unfinished flower development (ufd)

Reflections on the ABC model of flower development

The formulation of the ABC model by a handful of pioneer plant developmental geneticists was a seminal event in the quest to answer a seemingly simple question: how are flowers formed? Fast forward 30 years and this elegant model has generated a vibrant and diverse community, capturing the imagination of developmental and evolutionary biologists, structuralists, biochemists and molecular biologists alike. Together they have managed to solve many floral mysteries, uncovering the regulatory processes that generate the characteristic spatio-temporal expression patterns of floral homeotic genes, elucidating some of the mechanisms allowing ABC genes to specify distinct organ identities, revealing how evolution tinkers with the ABC to generate morphological diversity, and even shining a light on the origins of the floral gene regulatory network itself. Here we retrace the history of the ABC model, from its genesis to its current form, highlighting specific milestones along the way before drawing attention to some of the unsolved riddles still hidden in the floral alphabet.

Temporal Distinction between Male and Female Floral Organ Development in Nicotiana tabacum cv. Xanthi (Solanaceae)

Early floral developmental investigations provide crucial evidence for phylogenetic and molecular studies of plants. The developmental and evolutionary mechanisms underlying the variations in floral organs are critical for a thorough understanding of the diversification of flowers. Ontogenetic comparisons between anthers and pistil within single flowers were characterized over time in Nicotiana tabacum cv. Xanthi. The ages of 42 tobacco flower or flower primordia were estimated using corolla growth analysis. Results showed that the protodermal layer in carpel primordia contributes to carpel development by both anticlinal and periclinal divisions. Periclinal divisions in the hypodermal layer of the placenta were observed around 4.8 ± 1.3 days after the formation of early carpel primordia (ECP) and ovule initiation occurred 10.0 ± 0.5 days after ECP. Meiosis in anthers and ovules began about 8.9 ± 1.1 days and 14.4 ± 1.3 days after ECP, respectively. Results showed an evident temporal distinction between megasporogenesis and microsporogenesis. Flower ages spanned a 17-day interval, starting with flower primordia containing the ECP and anther primordia to the tetrad stage of meiosis in megasporocytes and the bicellular stage in pollen grains. These results establish a solid foundation for future studies in order to identify the developmental and molecular mechanisms responsible for the mating system in tobacco.

Exploration of miRNAs and target genes of cytoplasmic male sterility line in cotton during flower bud development

Cytoplasmic male sterility (CMS) lines provide crucial material to harness heterosis for crop plants, which serves as an important strategy for hybrid seed production. However, the molecular mechanism remains obscure. Although microRNAs (miRNAs) play important roles in vegetative growth and reproductive growth, there are few reports on miRNAs regulating the development of male sterility in Upland cotton. In present study, 12 small RNA libraries were constructed and sequenced for two development stages of flower buds from a CMS line and its maintainer line. Based on the results, 256 novel miRNAs were allocated to 141 new miRNA families, and 77 known miRNAs belonging to 54 conserved miRNA families were identified as well. Comparative analysis revealed that 61 novel and 10 conserved miRNAs were differentially expressed. Further transcriptome analysis identified 232 target genes for these miRNAs, which participated in cellular developmental process, cell death, pollen germination, and sexual reproduction. In addition, expression patterns of typical miRNA and the negatively regulated target genes, such as PPR, ARF, AP2, and AFB, were verified by qRT-PCR in cotton flower buds. These targets were previously reported to be related to reproduction development and male sterility, suggesting that miRNAs might act as regulators of CMS occurrence. Some miRNAs displayed specific expression profiles in special developmental stages of CMS line and its fertile hybrid (F₁). Present study offers new information on miRNAs and their related target genes in exploiting CMS mechanism, and revealing the miRNA regulatory networks in Upland cotton.

Ethylene Role in Plant Growth, Development and Senescence: Interaction with Other Phytohormones

The complex juvenile/maturity transition during a plant's life cycle includes growth, reproduction, and senescence of its fundamental organs: leaves, flowers, and fruits. Growth and senescence of leaves, flowers, and fruits involve several genetic networks where the phytohormone ethylene plays a key role, together with other hormones, integrating different signals and allowing the onset of conditions favorable for stage progression, reproductive success and organ longevity. Changes in ethylene level, its perception, and the hormonal crosstalk directly or indirectly regulate the lifespan of plants. The present review focused on ethylene's role in the development and senescence processes in leaves, flowers and fruits, paying special attention to the complex networks of ethylene crosstalk with other hormones. Moreover, aspects with limited information have been highlighted for future research, extending our understanding on the importance of ethylene during growth and senescence and boosting future research with the aim to improve the qualitative and quantitative traits of crops.