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SUMMARY: 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. Significance Statement: In this paper, we demonstrated that zinc finger protein GIS3 is the key regulator to control root hair development in Arabidopsis. Further experiments demonstrated that GIS3, RHD2, and RHD4 are required for root hair development in response to ethylene and cytokinin signaling. More importantly, the molecular and genetic experiments reveal that GIS3 directly binds to the promoter of RHD2 and RHD4 to regulate root hair elongation in Arabidopsis. These results will provide a novel function of zinc finger protein interacting with hormone signal to control root hair development and a better understanding of the network of zinc finger protein interact with root hair‐related genes to control root hair development in Arabidopsis. [ABSTRACT FROM AUTHOR]

N6‐methyladenosine (m6A) mRNA modification represents the most widespread form of internal modifications in eukaryotic mRNAs. In the model plant Arabidopsis thaliana, those known methyltransferases mainly deposit m6A 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 m6A methyltransferase that determines m6A modifications at over 2000 Arabidopsis transcripts predominantly in the coding region. Mutants of FIO1 show a decrease in global m6A mRNA methylation levels and an early‐flowering phenotype. Nanopore direct RNA sequencing reveals that FIO1 is required for establishing appropriate levels of m6A 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 m6A 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 m6A methyltransferase that mainly modifies the coding regions of transcripts, which underlies the key developmental transition from vegetative to reproductive growth in plants. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

RNA modifications constitute an essential layer of gene regulation in living organisms. As the most prevalent internal modification on eukaryotic mRNAs, N 6 -methyladenosine (m 6 A) exists in many plant species and requires the evolutionarily conserved methyltransferases, demethylases, and m 6 A binding proteins for writing, erasing, and reading m 6 A, respectively. In plants, m 6 A 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 m 6 A 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 m 6 A research in plants., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)