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Abstract Circadian clocks have long been hypothesized to tightly link cellular and physiological processes to the appropriate time within the 24-hour cycle of the Earth’s daily rotation. According to this hypothesis, circadian rhythms with cycle lengths that differ significantly from 24 hours would be disadvantageous, as they would generate a desynchronization between the endogenous and exogenous cycles that would place stress upon an organism through the required daily resetting at dawn. However, recent work has demonstrated that endogenous circadian cycles that differ from 24 hours by 2 hours or more are prevalent within the green lineage. Herein, we review recent work on the prevalence of, and adaptive advantages associated with, natural variation in circadian cycles. Based on known photoperiodic sensing mechanisms we also describe a set of principles that allow the same changes in circadian period to cause different plant responses. This fine-tuning of clock output pathways provides a flexible mechanism enabling plants to use a wide range of life history strategies for plant adaptation to different environmental niches. Further studies are needed to determine how variations of the clock and other signals are integrated in different plants. These studies highlight the circadian clocks’ position as a prime adaptation target for migration of plant species into new environmental ranges. 

Abstract Intercellular communication in plants, as in other multicellular organisms, allows cells in tissues to coordinate their responses for development and in response to environmental stimuli. Much of this communication is facilitated by plasmodesmata (PD), consisting of membranes and cytoplasm, that connect adjacent cells to each other. PD have long been viewed as passive conduits for the movement of a variety of metabolites and molecular cargoes, but this perception has been changing over the last two decades or so. Research from the last few years has revealed the importance of PD as signaling hubs and as crucial players in hormone signaling. The adoption of advanced biochemical approaches, molecular tools, and high-resolution imaging modalities has led to several recent breakthroughs in our understanding of the roles of PD, revealing the structural and regulatory complexity of these ‘protoplasmic connecting threads’. We highlight several of these findings that we think well illustrate the current understanding of PD as functioning at the nexus of plant physiology, development, and acclimation to the environment. 

Abstract The modification of seed shattering has been a recurring theme in rice evolution. The wild ancestor of cultivated rice disperses its seeds, but reduced shattering was selected during multiple domestication events to facilitate harvesting. Conversely, selection for increased shattering occurred during the evolution of weedy rice, a weed invading cultivated rice fields that has originated multiple times from domesticated ancestors. Shattering requires formation of a tissue known as the abscission zone (AZ), but how the AZ has been modified throughout rice evolution is unclear. We quantitatively characterized the AZ characteristics of relative length, discontinuity, and intensity in 86 cultivated and weedy rice accessions. We reconstructed AZ evolutionary trajectories and determined the degree of convergence among different cultivated varieties and among independent weedy rice populations. AZ relative length emerged as the best feature to distinguish high and low shattering rice. Cultivated varieties differed in average AZ morphology, revealing lack of convergence in how shattering reduction was achieved during domestication. In contrast, weedy rice populations typically converged on complete AZs, irrespective of origin. By examining AZ population-level morphology, our study reveals its evolutionary plasticity, and suggests that the genetic potential to modify the ecologically and agronomically important trait of shattering is plentiful in rice lineages. 

Hornworts are a deeply diverged lineage of bryophytes and a sister lineage to mosses and liverworts. Hornworts have an array of unique features that can be leveraged to illuminate not only the early evolution of land plants, but also alternative paths for nitrogen and carbon assimilation via cyanobacterial symbiosis and a pyrenoid-based CO2-concentrating mechanism (CCM), respectively. Despite this, hornworts are one of the few plant lineages with limited available genetic tools. Here we report an efficient biolistics method for generating transient expression and stable transgenic lines in the model hornwort, Anthoceros agrestis. An average of 569 (±268) cells showed transient expression per bombardment, with green fluorescent protein expression observed within 48–72 h. A total of 81 stably transformed lines were recovered across three separate experiments, averaging six lines per bombardment. We followed the same method to transiently transform nine additional hornwort species, and obtained stable transformants from one. This method was further used to verify the localization of Rubisco and Rubisco activase in pyrenoids, which are central proteins for CCM function. Together, our biolistics approach offers key advantages over existing methods as it enables rapid transient expression and can be applied to widely diverse hornwort species. 

Abstract The relationship between root, stem, and leaf hydraulic status and stomatal conductance during drought (field capacities: 100–25%) and drought recovery was studied in Helianthus annuus and five tree species (Populus×canadensis, Acer saccharum, A. saccharinum, Picea glauca, and Tsuga canadensis). Measurements of stomatal conductance (gs), organ water potential, and vessel embolism were performed and the following was observed: (i) cavitation only occurred in the petioles and not the roots or stems of tree species regardless of drought stress; (ii) in contrast, all H. annuus organs exhibited cavitation to an increasing degree from root to petiole; and (iii) all species initiated stomatal closure before cavitation events occurred or the expected turgor loss point was reached. After rewatering: (i) cavitated vessels in petioles of Acer species recovered whereas those of P. ×canadensis did not and leaves were shed; (ii) in H. annuus, cavitated xylem vessels were refilled in roots and petioles, but not in stems; and (iii) despite refilled embolisms in petioles of some species during drought recovery, gs never returned to pre-drought conditions. Conclusions are drawn with respect to the hydraulic segmentation hypothesis for above- and below-ground organs, and the timeline of embolism occurrence and repair is discussed. 

Abstract The growth, survival, and productivity of plants are constantly challenged by diverse abiotic stresses. When plants are exposed to stress for the first time, they can capture molecular information and store it as a form of memory, which enables them to competently and rapidly respond to subsequent stress(es). This process is referred to as a priming-induced or acquired stress response. In this review, we discuss how (i) the storage and retrieval of the information from stress memory modulates plant physiological, cellular, and molecular processes in response to subsequent stress(es), (ii) the intensity, recurrence, and duration of priming stimuli influences the outcomes of the stress response, and (iii) the varying responses at different plant developmental stages. We highlight current understanding of the distinct and common molecular processes manifested at the epigenetic, (post-)transcriptional, and post-translational levels mediated by stress-associated molecules and metabolites, including phytohormones. We conclude by emphasizing how unravelling the molecular circuitry underlying diverse priming-stimuli-induced stress responses could propel the use of priming as a management practice for crop plants. This practice, in combination with precision agriculture, could aid in increasing yield quantity and quality to meet the rapidly rising demand for food. 

Abstract The Snf1-related protein kinase 1 (SnRK1) is the plant homolog of the heterotrimeric AMP-activated protein kinase/sucrose non-fermenting 1 (AMPK/Snf1), which works as a major regulator of growth under nutrient-limiting conditions in eukaryotes. Along with its conserved role as a master regulator of sugar starvation responses, SnRK1 is involved in controlling the developmental plasticity and resilience under diverse environmental conditions in plants. In this review, through mining and analyzing the interactome and phosphoproteome data of SnRK1, we are highlighting its role in fundamental cellular processes such as gene regulation, protein synthesis, primary metabolism, protein trafficking, nutrient homeostasis, and autophagy. Along with the well-characterized molecular interaction in SnRK1 signaling, our analysis highlights several unchartered regions of SnRK1 signaling in plants such as its possible communication with chromatin remodelers, histone modifiers, and inositol phosphate signaling. We also discuss potential reciprocal interactions of SnRK1 signaling with other signaling pathways and cellular processes, which could be involved in maintaining flexibility and homeostasis under different environmental conditions. Overall, this review provides a comprehensive overview of the SnRK1 signaling network in plants and suggests many novel directions for future research.