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Proper orchestration of the thousands of biochemical processes that are essential to the life of every cell requires highly organized cellular compartmentalization of dedicated microenvironments. There are 2 ways to create this intracellular segregation to optimize cellular function. One way is to create specific organelles, enclosed spaces bounded by lipid membranes that regulate macromolecular flux in and out of the compartment. A second way is via membraneless biomolecular condensates that form due to to liquid-liquid phase separation. Although research on these membraneless condensates has historically been performed using animal and fungal systems, recent studies have explored basic principles governing the assembly, properties, and functions of membraneless compartments in plants. In this review, we discuss how phase separation is involved in a variety of key processes occurring in Cajal bodies (CBs), a type of biomolecular condensate found in nuclei. These processes include RNA metabolism, formation of ribonucleoproteins involved in transcription, RNA splicing, ribosome biogenesis, and telomere maintenance. Besides these primary roles of CBs, we discuss unique plant-specific functions of CBs in RNA-based regulatory pathways such as nonsense-mediated mRNA decay, mRNA retention, and RNA silencing. Finally, we summarize recent progress and discuss the functions of CBs in responses to pathogen attacks and abiotic stresses, responses that may be regulated via mechanisms governed by polyADP-ribosylation. Thus, plant CBs are emerging as highly complex and multifunctional biomolecular condensates that are involved in a surprisingly diverse range of molecular mechanisms that we are just beginning to appreciate. Biomolecular condensates in plants perform many more functions than were previously known; the roles of Cajal bodies, are explored in depth, shedding light on the numerous functions performed by biomolecular condensates in plants. [ABSTRACT FROM AUTHOR]

Summary: Peptide hormones are implicated in many important aspects of plant life and are usually synthesized as precursor proteins. In contrast to animals, data for plant peptide hormone maturation are scarce and the specificity of processing enzyme(s) is largely unknown. Here we tested a hypothesis that processing of prosystemin, a precursor of tomato (Solanum lycopersicum) wound hormone systemin, is performed by phytaspases, aspartate‐specific proteases of the subtilase family. Following the purification of phytaspase from tomato leaves, two tomato phytaspase genes were identified, the cDNAs were cloned and the recombinant enzymes were obtained after transient expression in Nicotiana benthamiana. The newly identified tomato phytaspases hydrolyzed prosystemin at two aspartate residues flanking the systemin sequence. Site‐directed mutagenesis of the phytaspase cleavage sites in prosystemin abrogated not only the phytaspase‐mediated processing of the prohormone in vitro, but also the ability of prosystemin to trigger the systemic wound response in vivo. The data show that the prohormone prosystemin requires processing for signal biogenesis and biological activity. The identification of phytaspases as the proteases involved in prosystemin maturation provides insight into the mechanisms of wound signaling in tomato. Our data also suggest a novel role for cell death‐related proteases in mediating defense signaling in plants. [ABSTRACT FROM AUTHOR]

Cajal bodies (CBs) are distinct sub-nuclear structures that are present in eukaryotic living cells and are often associated with the nucleolus. CBs play important roles in RNA metabolism and formation of RNPs involved in transcription, splicing, ribosome biogenesis, and telomere maintenance. Besides these primary roles, CBs appear to be involved in additional functions that may not be directly related to RNA metabolism and RNP biogenesis. In this review, we assess possible roles of plant CBs in RNA regulatory pathways such as nonsense-mediated mRNA decay and RNA silencing. We also summarize recent progress and discuss new non-canonical functions of plant CBs in responses to stress and disease. It is hypothesized that CBs can regulate these responsesviatheir interaction with poly(ADP ribose)polymerase (PARP), which is known to play an important role in various physiological processes including responses to biotic and abiotic stresses. It is suggested that CBs and their components modify PARP activities and functions. [ABSTRACT FROM PUBLISHER]