Plant transcription links environmental cues and phenotypic plasticity.

Photosynthetic organisms on land and in water produce the biomass and oxygen necessary for life on Earth. They are the first link in the food chain contributing to the life cycle. Plants, as sessile organisms, are forced to adapt to changing environmental constraints in order to ensure their growth and the faithful transmission of their genetic information. Plants are key elements for food, feed, human health, the environment and industry, and to improve plant production in a sustainable way is a major challenge for the future. In the current context of population growth and limitation of arable lands and fossil resources, global food security is intertwined with understanding how plants grow, differentiate and adapt to a changing environment. Indeed, plants have the ability to express different phenotypes from a given genotype, depending on multiple environmental stimuli as well as the capacity to regenerate their organs (e.g. leaves) in direct response to the environment (e.g. summer light conditions). This major phenotypic and developmental plasticity is a critical feature of plants and implies sophisticated molecular mechanisms regulating the expression of genes and the inheritance of expression patterns[1]. Indeed, environmental cues (e.g. light) have a strong impact on transcription in plant cells and changes in gene activity can also take place without altering the DNA sequence. These gene expression changes can pass on during cell divisions from one generation to the next (the foundation of “epigenetics”) or can be reversible once the environmental constraint fades. Plants partially achieve this growth and developmental plasticity by modulating the repertoire of transcribed genes. Advances in molecular biology and biotechnologies (e.g. high-throughput sequencing) have brought about a new dimension in the understanding of the mechanisms regulating the expression and transmission of genetic information in response to the environment. However, it also evidenced that post-transcriptional processes, such as alternative splicing, non-coding RNA mediated regulations or mRNA stability, also emerged as a key mechanism for gene regulation during plant adaptation to the environment[2]. Consequently, photosynthetic organisms, by their way of life, their phenotypic plasticity and their great ecological diversity constitute interesting experimental models to deciphering new ins and outs of transcriptional and epigenetic regulatory mechanisms in the regulation of developmental and phenotypic plasticity, adaptation to biotic and abiotic stresses and, in the longer term, the evolution of life in a changing environment. Due to these fascinating aspects of plant biology, in this issue of transcription, we decide to revise several emerging trends in plant transcriptional regulatory mechanisms and explore future research venues. We start with the review of de Leone et al [3]. which describes a thorough update on the transcriptional regulations involved in the circadian clock. Most living organisms possess an internal timekeeping mechanism known as the circadian clock to synchronize internal biological processes with diurnal and seasonal environmental changes. This review presents a detailed description of the transcriptional regulatory mechanisms and feedbacks involved in circadian clock regulations and how several core clock genes play a major role in the control of defense responses to plant pathogens. This demonstrates how circadian transcriptional rhythms are relevant for plant immunity. Then, Tognacca et al [4]. describe the