Congruity backcrossing as a means of creating genetic variability in self pollinated crops: seed morphology of Phaseolus vulgaris L. and P. acutifolius A. Gray hybrids

Summary Seeds of early generations of three reciprocal congruity-backcross (CBC) pedigrees, developed by backcrossing Phaseolus vulgaris-P. acutifolius hybrids to each of the parent species in alternate generations, exhibited a preponderance of traits (size, shape, color, and pattern) of the cytoplasmic parent. The large size of Red Cloud (V₁), the P. vulgaris parent common to all of the pedigrees, dominated pedigrees with V₁ as the cytoplasmic parent, while the small size and rounded or square shapes of the tepary parents, wild P. acutifolius var. acutifolius PI 263590 or G400445 (A₁₉), wild P. acutifolius var. latifolius PI 406622 (A₁₀), or cultivated P. acutifolius var. latifolius Serowi PI 319443 (A₉), were the majority phenotypes when P. acutifolius was the cytoplasmic parent. Continuing through the second cycle of CBC, that is the second backcross with each of the parent species or the fourth backcross, began an amelioration of the apparent cytoplasmic effect on gene expression, as reciprocal pedigrees became more alike, usually with intermediate expression of parental traits or the appearance of new traits. The large seed size of V₁ was recovered in hybrids with P. acutifolius cytoplasm and the kidney shape of V₁ became rare in hybrids with P. vulgaris cytoplasm. Although the tepary-bean parents represented two subspecies and both cultivated and wild P. acutifolius, the three sets of reciprocal-hybrid pedigrees with P. vulgaris Red Cloud are surprisingly similar. It may be that the exotic parent used to develop a CBC pedigree should be selected more for combining ability in the interspecific cross than for specific economic traits. While the number of generations (six or more) required to produce fertile, intermediate CBC hybrids (that did not require embryo rescue) may preclude routine use of this method by practical plant breeders, the crossability of advanced hybrids with both parental species and the amount of variability apparent in advanced-hybrids progenies suggests that CBC would be valuable for maintaining exotic germplasm in immediately useful forms.     

Rust-proofing wheat for a changing climate

This paper offers projections of potential effects of climate change on rusts of wheat and how we should factor in a changing climate when planning for the future management of these diseases. Even though the rusts of wheat have been extensively studied internationally, there is a paucity of information on the likely effects of a changing climate on the rusts and their influence on wheat production. Due to the lack of published empirical research we relied on the few published studies of other plant diseases, our own unpublished work and relevant information from the vast literature on rusts of wheat to prepare this overview. Three broad areas of potential risks from a changing climate were described: increased loss from wheat rusts, new rust pathotypes evolving faster and the reduced effectiveness of rust resistances. Increased biomass of wheat crops grown in the presence of elevated CO₂ concentrations and higher temperatures will increase the leaf area available for attack by the pathogen leading to increased inoculum production. If changed weather conditions were to accelerate the life cycle of a pathogen, the increased inoculum can lead to severe rust epidemics in many environments. Likewise should the effects of climate change result in more conducive conditions for rust development there will also be a corresponding increase in the rate of evolution of new pathotypes which could increase the rate of appearance of new virulences. The effectiveness of some rust resistance genes is influenced by temperature and crop development stage. Climate change may directly or indirectly influence the effectiveness of some resistance genes but this can not be ascertained due to a complete lack of knowledge. Since disease resistance breeding is a long term strategy it is important to determine if any of the important genes may become less effective due to climate change. Studies must be made to acquire new information on the rust disease triangle to increase the adaptive capacity of wheat under climate change. Leadership within the Borlaug Global Rust Initiative (BGRI) is needed to broker research on rust evolution and the durability of resistance under climate change.     

Microfluidic bubble logic

We demonstrate universal computation in an all-fluidic two-phase microfluidic system. Nonlinearity is introduced into an otherwise linear, reversible, low-Reynolds number flow via bubble-to-bubble hydrodynamic interactions. A bubble traveling in a channel represents a bit, providing us with the capability to simultaneously transport materials and perform logical control operations. We demonstrate bubble logic AND/OR/NOT gates, a toggle flip-flop, a ripple counter, timing restoration, a ring oscillator, and an electro-bubble modulator. These show the nonlinearity, gain, bistability, synchronization, cascadability, feedback, and programmability required for scalable universal computation. With increasing complexity in large-scale microfluidic processors, bubble logic provides an on-chip process control mechanism integrating chemistry and computation.     

Structural basis of a phototropin light switch

Phototropins are light-activated kinases important for plant responses to blue light. Light initiates signaling in these proteins by generating a covalent protein-flavin mononucleotide (FMN) adduct within sensory Per-ARNT-Sim (PAS) domains. We characterized the light-dependent changes of a phototropin PAS domain by solution nuclear magnetic resonance spectroscopy and found that an alpha helix located outside the canonical domain plays a key role in this activation process. Although this helix associates with the PAS core in the dark, photoinduced changes in the domain structure disrupt this interaction. We propose that this mechanism couples light-dependent bond formation to kinase activation and identifies a signaling pathway conserved among PAS domains.     

Nest inheritance is the missing source of direct fitness in a primitively eusocial insect

Animals that cooperate with nonrelatives represent a challenge to inclusive fitness theory, unless cooperative behavior is shown to provide direct fitness benefits. Inheritance of breeding resources could provide such benefits, but this route to cooperation has been little investigated in the social insects. We show that nest inheritance can explain the presence of unrelated helpers in a classic social insect model, the primitively eusocial wasp Polistes dominulus. We found that subordinate helpers produced more direct offspring than lone breeders, some while still subordinate but most after inheriting the dominant position. Thus, while indirect fitness obtained through helping relatives has been the dominant paradigm for understanding eusociality in insects, direct fitness is vital to explain cooperation in P. dominulus.     

Medulloblastoma growth inhibition by hedgehog pathway blockade

Constitutive Hedgehog (Hh) pathway activity is associated with initiation of neoplasia, but its role in the continued growth of established tumors is unclear. Here, we investigate the therapeutic efficacy of the Hh pathway antagonist cyclopamine in preclinical models of medulloblastoma, the most common malignant brain tumor in children. Cyclopamine treatment of murine medulloblastoma cells blocked proliferation in vitro and induced changes in gene expression consistent with initiation of neuronal differentiation and loss of neuronal stem cell-like character. This compound also caused regression of murine tumor allografts in vivo and induced rapid death of cells from freshly resected human medulloblastomas, but not from other brain tumors, thus establishing a specific role for Hh pathway activity in medulloblastoma growth.