Genetic Basis of Carnivorous Leaf Development

Plant carnivory is often manifested as dramatic changes in the structure and morphology of the leaf. These changes appear to begin early in leaf development. For example, the development of the Sarracenia purpurea leaf primordium is associated with the formation of an adaxial ridge, whose growth along with that of the leaf margin resulted in a hollow structure that later developed into a pitcher. In Nepenthes khasiana, pitcher formation occurs during the initial stages of leaf development, although this has not been shown at the primordial stage. The formation of the Utricularia gibba trap resulted from the growth of the dome-shaped primordium in both the longitudinal and transverse directions. Recent research has begun to unfold the genetic basis of the development of the carnivorous leaf. We review these findings and discuss them in relation to the flat-shaped leaves of the model plant Arabidopsis.

A new mathematical model of phyllotaxis to solve the genuine puzzle spiromonostichy

The view is widely accepted that the inhibitory effect of existing leaf primordia on new primordium formation determines phyllotactic patterning. Previous studies have shown that mathematical models based on such inhibitory effect can generate most of phyllotactic patterns. However, a few types of phyllotaxis still remain unaddressed. A notable example is costoid phyllotaxis showing spiromonostichy, which is characterized by a steep spiral with a small divergence angle and is unique to Costaceae plants. Costoid phyllotaxis has been called a "genuine puzzle" because it seems to disagree with the inhibitory effect-based mechanism. In an attempt to produce a steep spiral pattern, we developed a new mathematical model assuming that each leaf primordium emits not only the inhibitory effect but also some inductive effect. Computer simulations with the new model successfully generated a steep spiral pattern when these two effects met a certain relationship. The obtained steep spiral matched the real costoid phyllotaxis observed with Costus megalobractea. We also found by the mathematical model analysis that the early phyllotactic transition in the seedlings of this plant can be explained by the SAM enlargement.

What can the phylogeny of class I KNOX genes and their expression patterns in land plants tell us about the evolution of shoot development?

KNOX genes encode transcription factors (TFs), several of which act non-cell-autonomously. KNOX genes evolved in algae, and two classes, class I KNOX and class II KNOX genes, were already present in charophytes. In tracheophytes, class I KNOX genes are expressed in shoot apical meristems (SAMs) and thought to inhibit cell differentiation, whereas class II KNOX genes are expressed in mature organs regulating differentiation. In this review, we summarize the data available on gene families and expression patterns of class I and class II KNOX genes in embryophytes. The expression patterns of class I KNOX genes should be seen in the context of SAM structure and of leaf primordium development where the inhibition of cell differentiation needs to be lifted. Although the SAMs of angiosperms and gnetophytes almost always belong to the duplex type, several other types are distributed in gymnosperms, ferns, lycopods and bryophytes. KNOX gene families remained small (maximally five genes) in the representatives of bryophytes, lycopods and ferns examined thus far; however, they expanded to some extent in gymnosperms and, independently and much more strongly, in angiosperms. The growing sophistication of mechanisms to repress and re-induce class KNOX I expression played a major role in the evolution of leaf shape.

Genome-Wide Survey and Identification of AP2/ERF Genes Involved in Shoot and Leaf Development in Liriodendron Chinense

Background: Liriodendron chinense is a distinctive ornamental tree species due to its unique-shaped leaves and tulip-like flowers. The discovery of genes involved in leaf development and morphogenesis is critical for uncovering the underlying genetic basis of these traits. Genes in the AP2/ERF family were recognized as plant-specific transcription factors contributing to plant growth, hormone-induced development, ethylene response factors and stress responses. Results: In this study, we identified 104 putative AP2/ERF genes in the recently released Liriodendron genome database and RNA-seq dataset. Accordingly, all 104 genes were grouped into four subfamilies, including the AP2, ERF, RAV and Soloist subfamilies. This classification was further supported by the results of gene structure and conserved motif analyses. Moreover, based on the expression profiles of various tissues and organs, we discovered three LcAP2 genes as well as two VIII group genes that were significantly enriched in a shoot-specific manner by applying expression pattern and category enrichment analyses. Of these five genes, the relative expression levels of LcERF 94, LcERF 96 and LcERF 98 in the RT-qPCR assay were highly consistent with the RNA-seq results. Furthermore, we illustrated by dissection of Liriodendron shoots and subsequent qPCR assays that LcERF 94, LcERF 96 and LcERF 98 were expressed extensively in the early stage of leaf primordium development but rarely in tender leaves. In addition, these three genes displayed nuclear subcellular localizations through transient transformation of tobacco epidermal cells. Conclusions: Taken together, we identified all the AP2/ERF family members at the genome-wide level and provided candidates that might participate in the development and morphogenesis of the leaf primordium in L. chinense.

The Diverse Roles of Auxin in Regulating Leaf Development

Leaves, the primary plant organs that function in photosynthesis and respiration, have highly organized, flat structures that vary within and among species. In recent years, it has become evident that auxin plays central roles in leaf development, including leaf initiation, blade formation, and compound leaf patterning. In this review, we discuss how auxin maxima form to define leaf primordium formation. We summarize recent progress in understanding of how spatial auxin signaling promotes leaf blade formation. Finally, we discuss how spatial auxin transport and signaling regulate the patterning of compound leaves and leaf serration.

Remodelling of cell wall composition during leaf development in Lavoisiera mucorifera (Melastomataceae)

How does the deposition of cell wall components structure cell shape and function during leaf ontogenesis? Although this issue has been the subject of several studies, a wide variety of standards have been reported and many knowledge gaps remain. In this study we evaluated cell wall composition in leaf tissues of Lavoisiera mucorifera Mart. & Schrank ex DC. (Melastomataceae) regarding cellulose, pectin (homogalacturonans (HGs) and rhamnogalacturonans I (RGI)) and arabinogalactan protein (AGP) distribution during ontogenesis. Leaf primordium, as well as young and mature leaves, were submitted to histochemical analysis using calcofluor white and ruthenium red, and immunocytochemical analysis using primary monoclonal antibodies (JIM5, JIM7, LM2, LM5 and LM6). Results showed that the distribution of cell wall components depends on tissue and leaf developmental stage. At the beginning of cell differentiation in the leaf primordium, two main patterns of cellulose microfibril orientation occur: perpendicular and random. This initial microfibril arrangement determines final cell shape and leaf tissue functionality in mature leaves. During leaf development, especially in epidermal and collenchyma cells, the association of HGs with low methyl-esterified groups and cellulose guarantees mechanical support. As a result, cell wall properties, such as rigidity and porosity, may also be acquired by changes in cell wall composition and are associated with morphogenetic patterns in L. mucorifera.

Comparative development of simple and compound leaves in the genus Cecropia

Plants develop leaves that range from simple to compound in shape. The evolutionary divergence of simple and compound leaves has spurred research into identifying the cellular and molecular processes involved in determining leaf shape. The roles of various genes and signalling pathways have been characterized in specifying leaf shape; however, few studies have investigated leaf primordium structure and shoot apex organization throughout the development of both simple and compound leaves. Using Cecropia obtusa Trécul and Cecropia sciadophylla Martius, two putatively closely related species bearing simple palmate and palmately-compound leaves, respectively, we compared the morphogenesis of leaves of both species at the shoot apex. Analysis of shoot apices using scanning electron microscopy yielded a nonsignificant difference in leaf primordium divergence angles and plastochron ratios, suggesting that divergence of the two leaf types occurred independently of primordium organization and growth rate at the shoot apex. Qualitative analysis of primordium initiation and morphogenesis revealed that both species share highly homologous development, as primordium structure and lobe/leaflet initiation sites are complementary in both leaf types. Our observations suggest a high degree of conserved ontogeny in the developmental pathways underlying the morphogenesis of simple palmate and palmately-compound leaves in these two species.

Extended expression of MaKN1 contributes to the leaf morphology in aquatic forms of Myriophyllum aquaticum

Myriophyllum aquaticum (Vell.) Verdc. is heterophyllous in nature with highly dissected simple leaves consisting of several lobes. KNOX (KNOTTED1-LIKE HOMEOBOX) genes are believed to have played an important role in the evolution of leaf diversity. Up-regulation of KNOX during leaf primordium initiation can lead to leaf dissection in plants with simple leaves and, if overexpressed, can produce ectopic meristems on leaves. A previous study on KNOX gene expression in the aerial form of this species showed that this gene is expressed in the shoot apical meristem (SAM), as well as in leaf primordia P0 to P8. Based on these results, it was hypothesized that the prolonged expression of the MaKN1 (Myriophyllum aquaticum Knotted1-like homeobox) gene beyond P8, might play an important role in the generation of more lobes, longer lobes, and hydathode formation in the aquatic leaves of M. aquaticum. The technique of in situ hybridization was carried out using a previously sequenced 300 bp fragment of MaKN1 to determine the expression patterns of this gene in the shoot of aquatic forms of the plant. Expression patterns of MaKN1 revealed that the SAM and leaf primordia of aquatic forms of M. aquaticum at levels P0 (youngest) to P4 were distributed throughout these structures. The level of expression of this MaKN1 gene progressively became more localized to lobes in older leaf primordia (levels P5 to P12). Previous studies of aerial forms of this plant showed MaKN1 expression until P8. Our results with aquatic forms show that the highly dissected leaf morphology in aquatic forms was the result of the prolonged expression of MaKN1 beyond P8. This resulted in the formation of elongated and slightly more numerous lobes, and hydathodes in aquatic forms. These findings support the view that KNOX genes are important developmental regulators of leaf morphogenesis and have played an important role in the evolution of leaf forms in the plant kingdom.