Susan R. Singer

Axillary meristem development. Budding relationships between networks controlling flowering, branching, and photoperiod responsiveness.

Morphology in many animals is preordained during embryonic development and remains unchanged by environment. In contrast, vast differences in phenotype can occur in plants of identical genotype in different environments. Being sessile organisms, plants must rely on morphological and physiological

Developmental states associated with the floral transition

Floral initiation can be analyzed from a developmental perspective by focusing upon how developmental fates are imprinted, remembered, and expressed. This is not an altogether new perspective, since people studying flowering have been concerned for a long time with the commitment of meristems to form flowers and the morphological, cellular, and molecular changes associated with this commitment. What is novel is the emphasis on developmental states as opposed to physiological processes. This developmental focus indicates that there appear to be at least three major developmental states that are acquired and expressed in the process of a meristem initiating floral morphogenesis. The meristem cells must first become competent to respond to a developmental signal that evokes them into a florally determined state. The leaves are the usual source of this signal and a specific leaf may or may not have the capacity to be inductively active. When a leaf does develop the capacity for inductive activity, this capacity is usually correlated with the ontogeny of the leaf. Inductive activity, however, may be continually expressed as in some day-neutral plants or may be latent as in plants where the photoperiod is the external cue for activity. Competent shoot apical meristems respond to inductive leaf signal by being evoked into a florally determined state. Under permissive conditions this florally determined state is expressed as the initiation of floral morphogenesis. Many mechanisms have evolved to regulate entry into and expression of these developmental states. As we learn more about the developmental states associated with flowering and how they are acquired and expressed, we will understand better how the various patterns of flowering are related to one another as well as which developmental processes are common to all angiosperms.

Floral determination in the terminal and axillary buds of Nicotiana tabacum L.

Abstract The terminal and axillary buds of the day-neutral plant, Nicotiana tabacum cv. Wisconsin 38, become determined for floral development during the growth of the plant. This state of determination can be demonstrated with a simple experiment: buds determined for floral development produce the same number of nodes in situ and if rooted. After several months of growth and the production of many leaves, the terminal bud became determined for floral development within a period of about 2 days. After the terminal bud became florally determined, it produced four nodes and a terminal flower. The buds located in the axils of leaves borne just below the floral branches became florally determined 5 to 9 days after the terminal bud became florally determined. Since florally-determined axillary buds were not clonally derived from a florally-determined terminal meristem, axillary buds and the terminal bud acquired the state of floral determination independently. These data indicate that a pervasive signal induced a state of floral determination in competent terminal and axillary buds.

PROLIFERATING INFLORESCENCE MERISTEM, a MADS-Box Gene That Regulates Floral Meristem Identity in Pea

SQUAMOSA and APETALA1 are floral meristem identity genes from snapdragon (Antirrhinum majus) and Arabidopsis, respectively. Here, we characterize the floral meristem identity mutation proliferating inflorescence meristem(pim) from pea (Pisum sativum) and show that it corresponds to a defect in the PEAM4 gene, a homolog of SQUAMOSA and APETALA1. ThePEAM4 coding region was deleted in thepim-1 allele, and this deletion cosegregated with thepim-1 mutant phenotype. The pim-2 allele carried a nucleotide substitution at a predicted 5′ splice site that resulted in mis-splicing of pim-2 mRNA. PCR products corresponding to unspliced and exon-skipped mRNA species were observed. The pim-1 and pim-2 mutations delayed floral meristem specification and altered floral morphology significantly but had no observable effect on vegetative development. These floral-specific mutant phenotypes and the restriction ofPIM gene expression to flowers contrast with other known floral meristem genes in pea that additionally affect vegetative development. The identification of PIM provides an opportunity to compare pathways to flowering in species with different inflorescence architectures.

Polyploidy Did Not Predate the Evolution of Nodulation in All Legumes

Background Several lines of evidence indicate that polyploidy occurred by around 54 million years ago, early in the history of legume evolution, but it has not been known whether this event was confined to the papilionoid subfamily (Papilionoideae; e.g. beans, medics, lupins) or occurred earlier. Determining the timing of the polyploidy event is important for understanding whether polyploidy might have contributed to rapid diversification and radiation of the legumes near the origin of the family; and whether polyploidy might have provided genetic material that enabled the evolution of a novel organ, the nitrogen-fixing nodule. Although symbioses with nitrogen-fixing partners have evolved in several lineages in the rosid I clade, nodules are widespread only in legume taxa, being nearly universal in the papilionoids and in the mimosoid subfamily (e.g., mimosas, acacias) – which diverged from the papilionoid legumes around 58 million years ago, soon after the origin of the legumes. Methodology/Principal Findings Using transcriptome sequence data from Chamaecrista fasciculata, a nodulating member of the mimosoid clade, we tested whether this species underwent polyploidy within the timeframe of legume diversification. Analysis of gene family branching orders and synonymous-site divergence data from C. fasciculata, Glycine max (soybean), Medicago truncatula, and Vitis vinifera (grape; an outgroup to the rosid taxa) establish that the polyploidy event known from soybean and Medicago occurred after the separation of the mimosoid and papilionoid clades, and at or shortly before the Papilionoideae radiation. Conclusions The ancestral legume genome was not fundamentally polyploid. Moreover, because there has not been an independent instance of polyploidy in the Chamaecrista lineage there is no necessary connection between polyploidy and nodulation in legumes. Chamaecrista may serve as a useful model in the legumes that lacks a paleopolyploid history, at least relative to the widely studied papilionoid models.

Effective Practices in Undergraduate STEM Education Part 1: Examining the Evidence

Since the publication of reports in the late 1990s by the National Science Foundation (NSF; 1996) , the National Research Council (NRC; 1996 , 1999) , and the Boyer Commission on Educating Undergraduates in the Research University (1998) on the importance of improving undergraduate education in science, technology, engineering, and mathematics (STEM), at least 13 other federal civilian departments and agencies have spent billions of dollars on more than 200 programs to realize this goal. Most of that spending has come from the NSF and the National Institutes of Health (Government Accounting Office, 2005 ). Many private foundations also have invested hundreds of millions of dollars in efforts to improve undergraduate STEM education. For example, since 1988 the Howard Hughes Medical Institute has awarded more than

Inflorescence Architecture: A Developmental Genetics Approach

1.5 billion in grants to improve science education at the precollege and college levels.1 As a result of this financial support and commitment from the public and private sectors, research into and implementation of numerous and varied promising practices for teaching, learning, assessment, and institutional organization of undergraduate STEM education have been developed in recent years. These promising practices range from improvements in teaching in individual classrooms to changes in departments.2 They include increased prominence of campus and national centers for teaching excellence, professional development for faculty members (e.g., National Academies Summer Institute on Undergraduate Education in Biology,3 On the Cutting Edge: Professional Development for Geoscience Faculty4, First II5), and large outreach and dissemination efforts (e.g., Project Kaleidoscope,6 SENCER7). Virtually all of the new promising practices have focused on student-centered, inquiry-based approaches to teaching (summarized in Handelsman et al., 2007 ) or alternative assessments of student learning (e.g., see references in Deeds and Callen, 2006 ), compared with more traditional approaches to teaching that emphasize lecturing and multiple-choice or short-answer examinations. Some of these new approaches, such as Peer-Led Team Learning8 and Just in Time Teaching,9 have gained national recognition and prominence. Over the past decade, new practices have been implemented in vastly different grain sizes. Some have been targeted at specific classrooms, whereas others have focused on restructuring entire curricula. Still others have emphasized the role of assessment and evaluation of learning to improve teaching effectiveness (e.g., NRC, 2003a ,b ). Moreover, virtually all of these practices were developed independently from one another and have emphasized somewhat different goals. In addition, communications across the STEM disciplines and within their subdisciplines is often lacking. Thus, despite many years of effort and significant financial expenditure, surprisingly little is known about the collective impact of these approaches on the academic success of individuals and of different populations of students. For example, do more students who experience these new approaches to learning become sufficiently interested in these subject areas to want to take additional STEM courses compared with students from more traditional courses? Do these students succeed in higher-level STEM courses? Do they retain more information over longer periods and understand concepts more deeply? Are they better able to apply what they have learned in one context to others? At the institutional and professional levels, are faculty willing to change their teaching when presented with evidence that certain approaches to teaching are more effective than others? Data from valid and reliable assessment instruments, such as concept inventories (Hestenes et al., 1992 ; Mazur, 1997 ; Hake, 1998 ; Krause, 2004 10; Garvin-Doxas et al., 2007 ; Garvin-Doxas and Klymkowsky, 2008 ; Klymkowsky and Garvin-Doxas, 2008 ; Smith et al., 2008 ; also see http://gci.lite.msu.edu), often show that students do not understand concepts deeply; when faculty are presented with such data, are they actively reassessing their own approaches to undergraduate teaching? At the national level, how effective are these promising practices in changing the institutional culture of higher education toward acceptance and adoption of new approaches to undergraduate teaching, student learning, assessment of learning, and the balance of professional responsibilities of STEM faculty and within STEM departments? Given significant institutional differences in approaches and intended audiences, is enough evidence emerging to indicate that certain approaches to undergraduate teaching and learning “transcend” these differences? Can these approaches be adopted to engage the broad spectrum of undergraduate student audiences in the kinds of learning that will be required to address the large, complex problems that must be addressed in the twenty-first century?

Selection of amitrole tolerant tobacco calli and the expression of this tolerance in regenerated plants and progeny

We are characterizing a suiteof Pisum sativum mutants that alter inflorescence architecture to construct a model for the genetic regulation of inflorescence development in a plant with a compound raceme. Such a model, when compared with those created forAntirrhinum majus andArabidopsis thaliana, both of which have simple racemes, should provide insight into the evolution of the development of inflorescence architecture. The highly conserved nature of cloned genes that regulate reproductive development in plants and the morphological similarities among our mutants and those identified inA. majus andA. thaliana enhance the probability that a developmental genetics approach will be fruitful. Here we describe sixP. sativum mutants that affect morphologically and architecturally distinct aspects of the inflorescence, and we analyze interactions among these genes. Both vegetative and inflorescence growth of the primary axis is affected byUNIFOLIA TA, which is necessary for the function ofDETERMINATE (DET).DET maintains indeterminacy in the first-order axis. In its absence, the meristem differentiates as a stub covered with epidermal hairs.DET interacts withVEGETATIVE1 (VEG1).VEG1 appears essential for second-order inflorescence (I2) development.veg1 mutants fail to flower or differentiate the I2 meristem into a rudimentary stub,det veg1 double mutants produce true terminal flowers with no stubs, indicating that two genes must be eliminated for terminal flower formation inP. sativum, whereas elimination of a single gene accomplishes this inA. thaliana andA. majus. NEPTUNE also affects I2 development by limiting to two the number of flowers produced prior to stub formation. Its role is independent ofDET, as indicated by the additive nature of the double mutantdet nep. UNI, BROC, and PIM all play roles in assigning floral meristem identity to the third-order branch.pim mutants continue to produce inflorescence branches, resulting in a highly complex architecture and aberrant flowers.uni mutants initiate a whorl of sepals, but floral organogenesis is aberrant beyond that developmental point, and the double mutantuni pim lacks identifiable floral organs. A wild-type phenotype is observed inbroc plants, butbroc enhancesthe pim phenotype in the double mutant, producing inflorescences that resemble broccoli. Collectively these genes ensure that only the third-order meristem, not higher- or lower-order meristems, generates floral organs, thus precisely regulating the overall architecture of the plant.

Venturing Beyond Beans and Peas: What Can We Learn from Chamaecrista?

SummaryThirty-one clones capable of growth in the presence of 1.9×10−4 M amitrole (3-amino-1,2,4-triazole) were isolated from non-mutagenized cell suspensions of haploid Nicotiana tabacum cv. ‘Wisconsin 38’ plants at a frequency of 2.5×10−8. Seven clones retained tolerance when grown on selective medium for three years. When clones were cultured in the absence of amitrole, tolerance persisted for 9 months in five clones. Some plants regenerated from three amitrole-tolerant clones were tolerant. Seven amitrole-tolerant clones were isolated from diploid N. tabacum cell suspensions and R plant tolerance was followed through two sexual generations. Simple Mendelian inheritance patterns were not observed.

Biology Education Research: Lessons and Future Directions

Expanding legume research beyond the model members of the subfamily Papilionoideae (papilionoids) is necessary if we wish to capture more of the diversity of the enormous, economically important legume family. Chamaecrista fasciculata is emerging as a nonpapilionoid model, belonging to the