Cho, H.-T. | Search bioRxiv

bioRxiv2023

H2A.X mutants exhibit enhanced DNA demethylation in Arabidopsis thaliana

H2A.X is an H2A variant histone in eukaryotes, unique for its ability to respond to DNA damage, initiating the DNA repair pathway. H2A.X replacement within the histone octamer is mediated by the FAcilitates Chromatin Transactions (FACT) complex, a key chromatin remodeler. FACT is required for DEMETER (DME)-mediated DNA demethylation at certain loci in Arabidopsis thaliana female gametophytes during reproduction, though it is not known how FACT targets DME sites. Here, we investigated whether H2AX is involved in DME- and FACT-mediated DNA demethylation during Arabidopsis reproduction. We show that h2a.x mutants are more sensitive to genotoxic stress, consistent with previous reports. H2A.X fused to the Green Fluorescent Protein (GFP) gene under the H2A.X promoter was highly expressed in newly developing Arabidopsis tissues, including in male and female gametophytes. We examined DNA methylation in h2a.x developing seeds using whole genome bisulfite sequencing, and found that CG DNA methylation in the developing endosperm, but not the embryo, is decreased genome-wide in h2a.x mutants, predominately in transposons and intergenic DNA. Hypomethylated sites overlapped 62 % with canonical DME loci. These data indicate that H2A.X is not required for DME function, but is important for DNA methylation homeostasis in the unique chromatin environment of Arabidopsis endosperm.

plant biology↗

bioRxiv2017

The Molecular Link Between Auxin And ROS-Mediated Polar Growth

Root hair polar growth is endogenously controlled by auxin and sustained by oscillating levels of reactive oxygen species (ROS). These cells extend several hundred-fold their original size toward signals important for plant survival. Although their final cell size is of fundamental importance, the molecular mechanisms that control it remain largely unknown. Here, we show that ROS production is controlled by the transcription factors RSL4, which in turn is transcriptionally regulated by auxin through several Auxin Responsive Factors (ARFs). In this manner, auxin controls ROS-mediated polar growth by activating RSL4, which then upregulates the expression of genes encoding NADPH oxidases (also known as RBOHs, RESPIRATORY BURST OXIDASE HOMOLOG proteins) and Class-III Peroxidases (PER), which catalyse ROS production. Chemical or genetic interference with the ROS balance or peroxidase activity affect root hair final cell size. Overall, our findings establish a molecular link between auxin regulated ARFs-RSL4 and ROS-mediated polar root hair growth.\n\nSignificance StatementTip-growing root hairs are excellent model systems to decipher the molecular mechanism underlying reactive oxygen species (ROS)-mediated cell elongation. Root hairs are able to expand in response to external signals, increasing several hundred-fold their original size, which is important for survival of the plant. Although their final cell size is of fundamental importance, the molecular mechanisms that control it remain largely unknown. In this study, we propose a molecular mechanism that links the auxin-Auxin Response Factors (ARFs) module to activation of RSL4, which directly targets genes encoding ROS-producing enzymes, such as NADPH oxidases (or RBOHs) and secreted type-III peroxidases (PERs). Activation of these genes impacts apoplastic ROS homeostasis, thereby stimulating root hair cell elongation.

plant biology↗