KNOTTEDI-like homeobox (KNOXI) genes regulate development of the leaf from the shoot apical meristem (SAM) and may regulate leaf form. We examined KNOXI expression in SAMs of various vascular plants and found that KNOXI expression correlated with complex leaf primordia. However, complex primordia may mature into simple leaves. Therefore, not all simple leaves develop similarly, and final leaf morphology may not be an adequate predictor of homology.

Two Norway spruce (Picea abies (L.) Karst.) genes belonging to class I of the KNOTTED1-like homeobox (KNOX) genes, HBK2 and HBK3, were cloned with PCR-based methods. The expression of these and a previously characterised related gene, HBK1, in different organs and during somatic embryogenesis was studied with RT-PCR. Transcripts of all three genes were detected in stems, roots and in cone buds, but not in needles. HBK1 and HBK3 are expressed throughout development in a normal cell line with embryogenic potential and in a cell line unable to form somatic embryos. HBK2 is expressed in the normal cell line, but not in the developmentally arrested cell line. This suggests that the HBK2 gene is involved in the somatic embryo development.

In higher plants, the shoot apical meristem generates the radially symmetrical stem and also produces, in succession, bilaterally symmetrical lateral organs called leaves. Photosynthetic light capture occurs in leaves. In addition, leaves may also function to perceive and transmit environmental

Knotted-like (KNOX) proteins constitute a group of homeodomain proteins involved in pattern formation in developing tissues of angiosperms and other green plants. We conducted phylogenetic analyses of nucleotide and amino acid sequences of all known KNOX proteins in order to examine their evolution. Our analyses reveal two groups of KNOX proteins, classes I and II. Dicot and monocot sequences occur in both classes, indicating that the protein classes arose prior to the origin of the monocots. A conifer (Picea) sequence is nested within class I, suggesting that there are likely to be other copies of KNOX genes in this and other conifers. The orthology of several grass genes (including Zea Kn1, ZMKN1) is strongly supported by phylogenetic and synteny analyses. However, no compelling evidence supports the hypothesis of orthology previously proposed for several dicot genes and ZMKN1. Analysis of expression patterns suggests that the ancestral KNOX gene was expressed in all plant parts and that the propensity to be downregulated in roots and leaves evolved in the class I genes.

Leaves, the plant organs responsible for capturing and converting most of the 170 billion metric tons of carbon fixed globally each year, can be broadly grouped into two morphological categories: simple and compound. Although simple-leaved species such as corn and Arabidopsis have traditionally been favored model systems for studying leaf development, recent years have seen an increase in genetic and molecular studies of compound leaf development. Two compound-leaved species in particular have emerged as model systems: tomato and pea. A variety of mutations which alter leaf morphology in these species have been described, and analyses of these mutations have allowed the construction of testable models of leaf development. Also, the knotted-like homeobox (KNOX) genes, which were originally discovered as regulators of meristem function, now appear to have a role in compound leaf development. In addition to the recent genetic and molecular analyses of tomato and pea, insight into the nature of compound leaf development may be gained through the study of (a) heteroblasty and heterophylly, phenomena in which a range of leaf forms can be produced by a single shoot, and (b) the evolutionary origins of compound leaves.

Homeodomain proteins are transcription factors that play a critical role in early development in eukaryotes. These proteins previously have been classified into numerous subgroups whose phylogenetic relationships are unclear. Our phylogenetic analysis of representative eukaryotic sequences suggests that there are two major groups of homeodomain proteins, each containing sequences from angiosperms, metazoa, and fungi. This result, based on parsimony and neighbor-joining analyses of primary amino acid sequences, was supported by two additional features of the proteins. The two protein groups are distinguished by an insertion/deletion in the homeodomain, between helices I and II. In addition, an amphipathic alpha-helical secondary structure in the region N terminal of the homeodomain is shared by angiosperm and metazoan sequences in one group. These results support the hypothesis that there was at least one duplication of homeobox genes before the origin of angiosperms, fungi, and metazoa. This duplication, in turn, suggests that these proteins had diverse functions early in the evolution of eukaryotes. The shared secondary structure in angiosperm and metazoan sequences points to an ancient conserved functional domain.

Nuclear DNA content of 62 species of angiosperms including 52 monocotyledons and ten dicotyledons has been estimated by flow cytometry using Nicotiana tabacum var. Xanthi as the internal standard. These data, considered together with previous data on diploid species, suggest the following: 1) Most families and orders of monocotyledons have small genomes. Contrary to the general impression that monocotyledons are a group characterized by large genomes, genomes of over 20 pg/2C nucleus occur only in the Liliiflorae, Commelinales, Alismatales, and Araceae. 2) Variation within families ranges from two- to 56-fold, but is two- to fivefold in most families. Thus extraordinary variation in genome size appears to be limited to particular lineages, perhaps owing to some shared feature that facilitates such variation. 3) Endopolyploidy is not observed in the leaves of the species studied, although it has been reported to occur in the roots of several monocotyledons. This suggests that an examination of the basis for this difference between the roots and leaves of monocotyledons may provide clues to the mechanisms that regulate endopolyploidization in these organs.

Despite long-standing interest in reconstructing rates of branching in the history of groups and recent attempts to use cladistic information to make inferences about such rates, the conditions under which genealogy affects rate reconstruction have not been demonstrated because studies of branching rates rely on methods that either ignore genealogy (and focus on changes in species richness through time) or do not reconstruct absolute rates. We consider stochastic and deterministic approaches that associate branching rates with branches of a phylogeny, allowing the influence of genealogy to be directly assessed. Both approaches assume that the phylogeny is known. The stochastic approach uses maximum likelihood to estimate one or more parameters of a Yule model in which individual lineages branch according to a Poisson process. In a model with only one rate parameter over the entire tree, genealogy affects the estimation of rate whenever some taxa are not extant (i.e., are known only from fossils) or are direct descendants of fossils of known age. In more complex multiparameter models, the estimated rates always depend on genealogy regardless of when the taxa are observed in time. The deterministic model uses nonlinear optimization methods to reconstruct local branching rates in a tree. This procedure minimizes the transformation in local rate required by the data on topology and times of occurrence. A uniform tree need not entail any transformation in local rate, but a nonuniform tree does. Genealogy therefore affects reconstructed branching rates in both deterministic and stochastic approaches. The approaches are illustrated using Vrba's phylogeny of fossil and extant African bovids.

Journal Article The Growth of Phylogenetic Information and the Need for a Phylogenetic Data Base Get access M. J. Sanderson, M. J. Sanderson 1Department of Ecology and Evolutionary Biology, University of ArizonaTucson, Arizona 85721, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar B. G. Baldwin, B. G. Baldwin 1Department of Ecology and Evolutionary Biology, University of ArizonaTucson, Arizona 85721, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar G. Bharathan, G. Bharathan 1Department of Ecology and Evolutionary Biology, University of ArizonaTucson, Arizona 85721, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar C. S. Campbell, C. S. Campbell 2Department of Plant Biology and Pathology, University of MaineOrono, Maine 04469, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar C. von Dohlen, C. von Dohlen 1Department of Ecology and Evolutionary Biology, University of ArizonaTucson, Arizona 85721, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar D. Ferguson, D. Ferguson 1Department of Ecology and Evolutionary Biology, University of ArizonaTucson, Arizona 85721, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar J. M. Porter, J. M. Porter 1Department of Ecology and Evolutionary Biology, University of ArizonaTucson, Arizona 85721, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar M. F. Wojciechowski, M. F. Wojciechowski 1Department of Ecology and Evolutionary Biology, University of ArizonaTucson, Arizona 85721, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar M. J. Donoghue M. J. Donoghue 1Department of Ecology and Evolutionary Biology, University of ArizonaTucson, Arizona 85721, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar Systematic Biology, Volume 42, Issue 4, December 1993, Pages 562–568, https://doi.org/10.1093/sysbio/42.4.562 Published: 01 December 1993 Article history Received: 15 January 1993 Accepted: 24 May 1993 Published: 01 December 1993