Gene expression homeostasis and chromosome architecture

A review of plant epigenetics through the lens of almond

While genomes were originally seen as static entities that stably held and organized genetic information, recent advances in sequencing have uncovered the dynamic nature of the genome. New conceptualizations of the genome include complex relationships between the environment and gene expression that must be maintained, regulated, and sometimes even transmitted over generations. The discovery of epigenetic mechanisms has allowed researchers to understand how traits like phenology, plasticity, and fitness can be altered without changing the underlying deoxyribonucleic acid sequence. While many discoveries were first made in animal systems, plants provide a particularly complex set of epigenetic mechanisms due to unique aspects of their biology and interactions with human selective breeding and cultivation. In the plant kingdom, annual plants have received the most attention; however, perennial plants endure and respond to their environment and human management in distinct ways. Perennials include crops such as almond, for which epigenetic effects have long been linked to phenomena and even considered relevant for breeding. Recent discoveries have elucidated epigenetic phenomena that influence traits such as dormancy and self-compatibility, as well as disorders like noninfectious bud failure, which are known to be triggered by the environment and influenced by inherent aspects of the plant. Thus, epigenetics represents fertile ground to further understand almond biology and production and optimize its breeding. Here, we provide our current understanding of epigenetic regulation in plants and use almond as an example of how advances in epigenetics research can be used to understand biological fitness and agricultural performance in crop plants.

Diversity, versatility and complexity of bacterial gene regulation mechanisms: opportunities and drawbacks for applications in synthetic biology

Gene expression occurs in two essential steps: transcription and translation. In bacteria, the two processes are tightly coupled in time and space, and highly regulated. Tight regulation of gene expression is crucial. It limits wasteful consumption of resources and energy, prevents accumulation of potentially growth inhibiting reaction intermediates, and sustains the fitness and potential virulence of the organism in a fluctuating, competitive and frequently stressful environment. Since the onset of studies on regulation of enzyme synthesis, numerous distinct regulatory mechanisms modulating transcription and/or translation have been discovered. Mostly, various regulatory mechanisms operating at different levels in the flow of genetic information are used in combination to control and modulate the expression of a single gene or operon. Here, we provide an extensive overview of the very diverse and versatile bacterial gene regulatory mechanisms with major emphasis on their combined occurrence, intricate intertwinement and versatility. Furthermore, we discuss the potential of well-characterized basal expression and regulatory elements in synthetic biology applications, where they may ensure orthogonal, predictable and tunable expression of (heterologous) target genes and pathways, aiming at a minimal burden for the host.

The codon sequences predict protein lifetimes and other parameters of the protein life cycle in the mouse brain

The homeostasis of the proteome depends on the tight regulation of the mRNA and protein abundances, of the translation rates, and of the protein lifetimes. Results from several studies on prokaryotes or eukaryotic cell cultures have suggested that protein homeostasis is connected to, and perhaps regulated by, the protein and the codon sequences. However, this has been little investigated for mammals in vivo. Moreover, the link between the coding sequences and one critical parameter, the protein lifetime, has remained largely unexplored, both in vivo and in vitro. We tested this in the mouse brain, and found that the percentages of amino acids and codons in the sequences could predict all of the homeostasis parameters with a precision approaching experimental measurements. A key predictive element was the wobble nucleotide. G-/C-ending codons correlated with higher protein lifetimes, protein abundances, mRNA abundances and translation rates than A-/U-ending codons. Modifying the proportions of G-/C-ending codons could tune these parameters in cell cultures, in a proof-of-principle experiment. We suggest that the coding sequences are strongly linked to protein homeostasis in vivo, albeit it still remains to be determined whether this relation is causal in nature.