GLABROUS INFLORESCENCE STEMS3 binds to and activates RHD2 and RHD4 genes to promote root hair elongation in Arabidopsis.

Root hairs are crucial in the uptake of essential nutrients and water in plants. This study showed that a zinc finger protein, GIS3 is involved in root hair growth in Arabidopsis. The loss-of-function gis3 and GIS3 RNAi transgenic line exhibited a significant reduction in root hairs compared to the wild type. The application of 1-aminocyclopropane-1-carboxylic acid (ACC), an exogenous ethylene precursor, and 6-benzyl amino purine (BA), a synthetic cytokinin, significantly restored the percentage of hair cells in the epidermis in gis3 and induced GIS3 expression in the wild type. More importantly, molecular and genetic studies revealed that GIS3 acts upstream of ROOT HAIR DEFECTIVE 2 (RHD2) and RHD4 by binding to their promoters. Furthermore, exogenous ACC and BA application significantly induced the expression of RHD2 and RHD4, while root hair phenotype of rhd2-1, rhd4-1, and rhd4-3 was insensitive to ACC and BA treatment. We can therefore conclude that GIS3 modulates root hair development by directly regulating RHD2 and RHD4 expression through ethylene and cytokinin signals in Arabidopsis.

Shaping the landscape of N6-methyladenosine RNA methylation in Arabidopsis.

N 6-methyladenosine (m6A) modification on messenger RNAs (mRNAs) is deposited by evolutionarily conserved methyltransferases (writers). How individual m6A writers sculpt the overall landscape of the m6A methylome and the resulting biological impact in multicellular organisms remains unknown. Here, we systematically surveyed the quantitative m6A methylomes at single-nucleotide resolution and their corresponding transcriptomes in Arabidopsis (Arabidopsis thaliana) bearing respective impaired m6A writers. The m6A sites associated with the five Arabidopsis writers were located mostly within 3' untranslated regions with peaks at around 100 bp downstream of stop codons. m6A predominantly promoted the usage of distal poly(A) sites but had little effect on RNA splicing. Notably, impaired m6A writers resulted in hypomethylation and downregulation of transcripts encoding ribosomal proteins, indicating a possible correlation between m6A and protein translation. Besides the common effects on mRNA metabolism and biological functions uniquely exerted by different Arabidopsis m6A writers compared with their counterparts in human cell lines, our analyses also revealed the functional specificity of individual Arabidopsis m6A writers in plant development and response to stresses. Our findings thus reveal insights into the biological roles of various Arabidopsis m6A writers and their cognate counterparts in other multicellular m6A methyltransferase complexes.

TOP1α, UPF1, and TTG2 regulate seed size in a parental dosage-dependent manner.

Cues of maternal and paternal origins interact to control seed development, and the underlying molecular mechanisms are still far from clear. Here, we show that TOPOISOMERASE Iα (TOP1α), UP-FRAMESHIFT SUPPRESSOR 1 (UPF1), and TRANSPARENT TESTA GLABRA2 (TTG2) gametophytically, biparentally regulate seed size in Arabidopsis. TOP1α and UPF1 are mainly expressed in antipodal cells, and loss of their function leads to ectopic TTG2 expression in these female gametophytic cells. We further demonstrate that TOP1α and UPF1 directly repress TTG2 expression through affecting its chromatin status and determine its relative expression in antipodal cells versus sperm cells, which controls seed size in a dosage-dependent and parent-of-origin-dependent manner. The molecular interplay among these three genes explains their biparental gametophytic effect during diploidy and interploidy reciprocal crosses. Taken together, our findings reveal a molecular framework of parental interaction for seed size control.

N6-methyladenosine-mediated feedback regulation of abscisic acid perception via phase-separated ECT8 condensates in Arabidopsis.

N6-methyladenosine (m6A) is the most abundant internal modification in eukaryotic mRNAs, yet how plants recognize this chemical modification to swiftly adjust developmental plasticity under environmental stresses remains unclear. Here we show that m6A mRNA modification and its reader protein EVOLUTIONARILY CONSERVED C-TERMINAL REGION 8 (ECT8) act together as a key checkpoint for negative feedback regulation of abscisic acid (ABA) signalling by sequestering the m6A-modified ABA receptor gene PYRABACTIN RESISTANCE 1-LIKE 7 (PYL7) via phase-separated ECT8 condensates in stress granules in response to ABA. This partially depletes PYL7 mRNA from its translation in the cytoplasm, thus reducing PYL7 protein levels and compromising ABA perception. The loss of ECT8 results in defective sequestration of m6A-modified PYL7 in stress granules and permits more PYL7 transcripts for translation. This causes overactivation of ABA-responsive genes and the consequent ABA-hypersensitive phenotypes, including drought tolerance. Overall, our findings reveal that m6A-mediated sequestration of PYL7 by ECT8 in stress granules negatively regulates ABA perception, thereby enabling prompt feedback regulation of ABA signalling to prevent plant cell overreaction to environmental stresses.

FIONA1-Mediated m6 A Modification Regulates the Floral Transition in Arabidopsis.

N6 -methyladenosine (m6 A) mRNA modification represents the most widespread form of internal modifications in eukaryotic mRNAs. In the model plant Arabidopsis thaliana, those known methyltransferases mainly deposit m6 A at their target transcripts near the stop codon or in the 3' untranslated region. Here, it is reported that FIONA1 (FIO1), a human METTL16 ortholog, acts as a hitherto unknown m6 A methyltransferase that determines m6 A modifications at over 2000 Arabidopsis transcripts predominantly in the coding region. Mutants of FIO1 show a decrease in global m6 A mRNA methylation levels and an early-flowering phenotype. Nanopore direct RNA sequencing reveals that FIO1 is required for establishing appropriate levels of m6 A preferentially in the coding sequences of a subset of protein-coding transcripts, which is associated with changes in transcript abundance and alternative polyadenylation. It is further demonstrated that FIO1-mediated m6 A methylation determines the mRNA abundance of a central flowering integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and its upstream regulators, thus preventing premature flowering. The findings reveal that FIO1 acts as a unique m6 A methyltransferase that mainly modifies the coding regions of transcripts, which underlies the key developmental transition from vegetative to reproductive growth in plants.

N6-methyladenosine modification underlies messenger RNA metabolism and plant development.

RNA modifications constitute an essential layer of gene regulation in living organisms. As the most prevalent internal modification on eukaryotic mRNAs, N6-methyladenosine (m6A) exists in many plant species and requires the evolutionarily conserved methyltransferases, demethylases, and m6A binding proteins for writing, erasing, and reading m6A, respectively. In plants, m6A affects many aspects of mRNA metabolism, including alternative polyadenylation, secondary structure, translation, and decay, which underlies various plant developmental processes and stress responses. Here, we discuss the recent progress in understanding the roles of m6A modification in mRNA metabolism and their mechanistic link with plant development and stress responses. We also highlight some outstanding questions and provide an outlook on future prospects of m6A research in plants.

Mesostigma viride Genome and Transcriptome Provide Insights into the Origin and Evolution of Streptophyta.

The Streptophyta include unicellular and multicellular charophyte green algae and land plants. Colonization of the terrestrial habitat by land plants is a major evolutionary event that has transformed the planet. So far, lack of genome information on unicellular charophyte algae hinders the understanding of the origin and the evolution from unicellular to multicellular life in Streptophyta. This work reports the high-quality reference genome and transcriptome of Mesostigma viride, a single-celled charophyte alga with a position at the base of Streptophyta. There are abundant segmental duplications and transposable elements in M. viride, which contribute to a relatively large genome with high gene content compared to other algae and early diverging land plants. This work identifies the origin of genetic tools that multicellular Streptophyta have inherited and key genetic innovations required for the evolution of land plants from unicellular aquatic ancestors. The findings shed light on the age-old questions of the evolution of multicellularity and the origin of land plants.

Messenger RNA Modifications in Plants.

Over 160 distinct RNA modifications are known and collectively termed the epitranscriptome. Some of these modifications have been discovered in mRNA, uncovering a new layer of gene regulation. Transcriptome-wide mapping of epitranscriptomic codes and the discovery of their writers, erasers, and readers that dynamically install, remove, and interpret RNA modifications, respectively, are fundamental to understanding the epitranscriptome. Recent technologies have enabled the transcriptome-wide profiling of several mRNA modifications in Arabidopsis thaliana, providing key insights into regulating these modifications and their effects on plant development. Here we review technological innovations and recent progress in epitranscriptomics, with specific focus on N6-methyladenosine (m6A), 5-methylcytosine (m5C), uridylation, and their roles in multiple aspects of plant development.

Chemically induced virus resistance in Arabidopsis thaliana is independent of pathogenesis-related protein expression and the NPR1 gene.

Salicylic acid (SA) treatment triggers inhibition of replication or movement of several positive-sense RNA plant viruses in tobacco. This resistance can also be stimulated by nonlethal concentrations of cyanide and antimycin A (AA) without triggering induction of pathogenesis-related PR-1 protein genes. In two ecotypes of Arabidopsis thaliana (Columbia and Nössen), SA-induced resistance to a tobamovirus, Turnip vein clearing virus (TVCV), was also induced by nonlethal concentrations of cyanide and AA without concomitant induction of PR-1 gene expression. Furthermore, chemically induced resistance to TVCV, as well as the induction of the plant mitochondrial alternative oxidase (a potential target for the chemicals), was independent of NPR1, a gene that plays a key role downstream of SA in the induction of PR proteins. The chemically induced resistance to TVCV appeared to be due to inhibition of replication at the site of inoculation. Taken together, these results show that in Arabidopsis, as in tobacco, resistance to viruses can be induced via a distinct branch of the defensive signal transduction pathway. This suggests that the existence of this virus-specific branch may be widespread among plants.

In vitro propagation of Australian native ornamental plant, Scaevola.

In this chapter, we describe a robust method for the micropropagation of Australian fan flower, Scaevola, a native plant increasingly being used in the ornamental horticulture industry. Shoot segments from different species of Scaevola can be successfully multiplied following this protocol. Multiple shoots can be obtained in hormone-free Murashige and Skoog medium. The regenerated shoot is rooted on hormone-free medium within 4-6 weeks. In vitro grown plantlets readily adapt to glasshouse conditions.