From the archives: Lignin chemistry and vascular cell capacity, chromosome organization in rice meiosis, and circadian clock setting by imbibition

Abstract

December 2022: Lignin chemistry and vascular cell capacity Lignin is a biopolymer in the cell walls of most land plants. Besides its key role in structural support, it is required for water conduction and serves as a physical barrier against pathogens. Lignin is assembled from a wide variety of mono-mers, and its composition greatly varies among plant species, tissues, and cell types (Vanholme et al. 2019). Ménard et al. (2022) demonstrated the importance of lignin biochemistry in different tracheary element (TE) morphotypes in the plant xylem. Because these cells die before becoming functional, it was long believed that they were unable to adapt to developmental and environmental constraints. However, the authors demonstrated that TEs continue to accumulate lig-nin for more than 40 days postmortem, resulting in enhanced cell wall stiffness and resistance against negative pressure. All TE morphotypes had specific lignin biochemis-tries, differing in the amount of lignin, the chemical composition of the lignin units, and their position in longer monomers. Interfering with lignin levels and composition through pharmacologic and genetic approaches resulted in dramatic effects on sap conduction and the ability of plants to recover from drought stress (see Figure). This work showed that postmortem, dynamic fine-tuning of lignin biochemistry is an essential aspect of plant responses to developmental and environmental cues. More recent work of the same research group revealed that the cell type specificity of lignin chemistry is determined by combinations of different laccases (Blaschek et al. 2023). December 2018: Chromosome organization in rice meiosis Meiosis is crucial for sexual reproduction in eukaryotes and consists of 1 round of DNA replication followed by 2 rounds of chromosome segregation, resulting in the formation of haploid gametes. The first stage of meiotic prophase I, termed leptotene, is characterized by the gradual loading of cohesin onto the chromosomes to assemble them into thin, thread-structured units. Furthermore, repair of double-stranded DNA breaks (DSBs) is initiated during leptotene, enabling meiotic recombination. In 2018 Zhao et al. (2018) provided evidence for the key role of OsRR24/LEPTOTENE1 (LEPTO1), a type-B response regulator, in leptotene chromosome organization in rice. Response regulators are proteins that regulate cellular responses to environmental cues as part of 2-component signal transduction systems and are involved in a wide variety of cellular responses. The authors revealed that recruitment of meiosis-specific proteins and formation of meiotic DSBs was disturbed in the lepto1 mutant , resulting in the abolishment of meiotic recombination. Furthermore, they showed that LEPTO1 is required for mega-sporogenesis and that it likely functions as a transcriptional acti-vator. Yeast 2-hybrid assays demonstrated that LEPTO1 interacts with 2 authentic histidine phosphotransferase (AHP) proteins, which are members of the heat shock protein family. As such, AHP-mediated phosphorylation could be involved in regulating LEPTO1 activity. A year later, another research group confirmed these results in an independent study on another allelic sterile