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1. A transporter of 1‐aminocyclopropane‐1‐carboxylic acid affects thallus growth and fertility in Marchantia polymorpha

   https://doi.org/10.1111/nph.18510  

   Li, Dongdong ; Dierschke, Tom ; Roden, Stijn ; Chen, Kunsong ; Bowman, John L. ; Chang, Caren ; Van de Poel, Bram ( October 2022 , New Phytologist)

   In seed plants, 1‐aminocyclopropane‐1‐carboxylic acid (ACC) is the precursor of the plant hormone ethylene but also has ethylene‐independent signaling roles. Nonseed plants produce ACC but do not efficiently convert it to ethylene. InArabidopsis thaliana, ACC is transported by amino acid transporters, LYSINE HISTIDINE TRANSPORTER 1 (LHT1) and LHT2. In nonseed plants,LHThomologs have been uncharacterized.

   Here, we isolated an ACC‐insensitive mutant (Mpain) that is defective in ACC uptake in the liverwortMarchantia polymorpha. Mpaincontained a frameshift mutation (1 bp deletion) in the MpLHT1coding sequence, and was complemented by expression of a wild‐type MpLHT1transgene. Additionally, ACC insensitivity was re‐created in CRISPR/Cas9‐Mplht1knockout mutants. We found that MpLHT1 can also transportl‐hydroxyproline andl‐histidine.

   We examined the physiological functions of MpLHT1in vegetative growth and reproduction based on mutant phenotypes. Mpainand Mplht1plants were smaller and developed fewer gemmae cups compared to wild‐type plants. Mplht1mutants also had reduced fertility, and archegoniophores displayed early senescence.

   These findings reveal that MpLHT1 serves as an ACC and amino acid transporter inM. polymorphaand has diverse physiological functions. We propose that MpLHT1 contributes to homeostasis of ACC and other amino acids inM. polymorphagrowth and reproduction.

    

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2. H2A.X promotes endosperm-specific DNA methylation in Arabidopsis thaliana

   https://doi.org/10.1186/s12870-023-04596-y  

   Frost, Jennifer M. ; Lee, Jaehoon ; Hsieh, Ping-Hung ; Lin, Samuel J. H. ; Min, Yunsook ; Bauer, Matthew ; Runkel, Anne M. ; Cho, Hyung-Taeg ; Hsieh, Tzung-Fu ; Fischer, Robert L. ; et al ( November 2023 , BMC Plant Biology)

   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 inArabidopsis thalianafemale gametophytes during reproduction. Here, we sought to investigate whether H2A.X is involved in DME- and FACT-mediated DNA demethylation during reproduction.

   H2A.X is encoded by two genes in Arabidopsis genome,HTA3andHTA5. We generatedh2a.xdouble mutants, which displayed a normal growth profile, whereby flowering time, seed development, and root tip organization, S-phase progression and proliferation were all normal. However,h2a.xmutants were more sensitive to genotoxic stress, consistent with previous reports. H2A.X fused to Green Fluorescent Protein (GFP) under theH2A.Xpromoter was highly expressed especially in newly developing Arabidopsis tissues, including in male and female gametophytes, where DME is also expressed. We examined DNA methylation inh2a.xdeveloping seeds and seedlings using whole genome bisulfite sequencing, and found that CG DNA methylation is decreased genome-wide inh2a.xmutant endosperm. Hypomethylation was most striking in transposon bodies, and occurred on both parental alleles in the developing endosperm, but not the embryo or seedling.h2a.x-mediated hypomethylated sites overlapped DME targets, but also included other loci, predominately located in heterochromatic transposons and intergenic DNA.

   Our genome-wide methylation analyses suggest that H2A.X could function in preventing access of the DME demethylase to non-canonical sites. Overall, our data suggest that H2A.X is required to maintain DNA methylation homeostasis in the unique chromatin environment of the Arabidopsis endosperm.

    

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3. Genetic and physical interactions between the organellar mechanosensitive ion channel homologs MSL 1, MSL 2, and MSL 3 reveal a role for inter‐organellar communication in plant development

   https://doi.org/10.1002/pld3.124  

   Lee, Josephine S. ; Wilson, Margaret E. ; Richardson, Ryan A. ; Haswell, Elizabeth S. ( March 2019 , Plant Direct)

   Plant development requires communication on many levels, including between cells and between organelles within a cell. For example, mitochondria and plastids have been proposed to be sensors of environmental stress and to coordinate their responses. Here we present evidence for communication between mitochondria and chloroplasts during leaf and root development, based on genetic and physical interactions between threeMechanosensitive channel ofSmall conductance‐Like (MSL) proteins fromArabidopsis thaliana.MSLproteins areArabidopsishomologs of the bacterialMechanosensitivechannel ofSmall conductance (MscS), which relieves cellular osmotic pressure to protect against lysis during hypoosmotic shock.MSL1 localizes to the inner mitochondrial membrane, whileMSL2 andMSL3 localize to the inner plastid membrane and are required to maintain plastid osmotic homeostasis during normal growth and development. In this study, we characterized the phenotypic effect of a genetic lesion inMSL1, both in wild type and inmsl2 msl3mutant backgrounds.msl1single mutants appear wild type for all phenotypes examined. The characteristic leaf rumpling inmsl2 msl3double mutants was exacerbated in themsl1 msl2 msl3triple mutant. However, the introduction of themsl1lesion into themsl2 msl3mutant background suppressed othermsl2 msl3mutant phenotypes, including ectopic callus formation, accumulation of superoxide and hydrogen peroxide in the shoot apical meristem, decreased root length, and reduced number of lateral roots. All these phenotypes could be recovered by molecular complementation with a transgene containing a wild type version ofMSL1. In yeast‐based interaction studies,MSL1 interacted with itself, but not withMSL2 orMSL3. These results establish that the abnormalities observed inmsl2 msl3double mutants is partially dependent on the presence of functionalMSL1 and suggest a possible role for communication between plastid and mitochondria in seedling development.

    

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4. Iron Availability within the Leaf Vasculature Determines the Magnitude of Iron Deficiency Responses in Source and Sink Tissues in Arabidopsis

   https://doi.org/10.1093/pcp/pcac046  

   Nguyen, Nga T. ; Khan, Mather A. ; Castro–Guerrero, Norma A. ; Chia, Ju-Chen ; Vatamaniuk, Olena K. ; Mari, Stephane ; Jurisson, Silvia S. ; Mendoza-Cozatl, David G. ( April 2022 , Plant and Cell Physiology)

   Iron (Fe) uptake and translocation in plants are fine-tuned by complex mechanisms that are not yet fully understood. In Arabidopsis thaliana, local regulation of Fe homeostasis at the root level has been extensively studied and is better understood than the systemic shoot-to-root regulation. While the root system is solely a sink tissue that depends on photosynthates translocated from source tissues, the shoot system is a more complex tissue, where sink and source tissues occur synchronously. In this study, and to gain better insight into the Fe deficiency responses in leaves, we overexpressed Zinc/Iron-regulated transporter-like Protein (ZIP5), an Fe/Zn transporter, in phloem-loading cells (proSUC2::AtZIP5) and determined the timing of Fe deficiency responses in sink (young leaves and roots) and source tissues (leaves). Transgenic lines overexpressing ZIP5 in companion cells displayed increased sensitivity to Fe deficiency in root growth assays. Moreover, young leaves and roots (sink tissues) displayed either delayed or dampened transcriptional responses to Fe deficiency compared to wild-type (WT) plants. We also took advantage of the Arabidopsis mutant nas4x-1 to explore Fe transcriptional responses in the opposite scenario, where Fe is retained in the vasculature but in an unavailable and precipitated form. In contrast to proSUC2::AtZIP5 plants, nas4x-1 young leaves and roots displayed a robust and constitutive Fe deficiency response, while mature leaves showed a delayed and dampened Fe deficiency response compared to WT plants. Altogether, our data provide evidence suggesting that Fe sensing within leaves can also occur locally in a leaf-specific manner.

    

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5. Maternal nitric oxide homeostasis impacts female gametophyte development under optimal and stress conditions

   https://doi.org/10.1093/plcell/koae043  

   Wang, Junzhe ; Guo, Xiaolong ; Chen, Yijin ; Liu, Tianxiang ; Zhu, Jianchu ; Xu, Shengbao ; Vierling, Elizabeth ( February 2024 , The Plant Cell)

   In adverse environments, the number of fertilizable female gametophytes (FGs) in plants is reduced, leading to increased survival of the remaining offspring. How the maternal plant perceives internal growth cues and external stress conditions to alter FG development remains largely unknown. We report that homeostasis of the stress signaling molecule nitric oxide (NO) plays a key role in controlling FG development under both optimal and stress conditions. NO homeostasis is precisely regulated by S-nitrosoglutathione reductase (GSNOR). Prior to fertilization, GSNOR protein is exclusively accumulated in sporophytic tissues and indirectly controls FG development in Arabidopsis (Arabidopsis thaliana). In GSNOR null mutants, NO species accumulated in the degenerating sporophytic nucellus, and auxin efflux into the developing FG was restricted, which inhibited FG development, resulting in reduced fertility. Importantly, restoring GSNOR expression in maternal, but not gametophytic tissues, or increasing auxin efflux substrate significantly increased the proportion of normal FGs and fertility. Furthermore, GSNOR overexpression or added auxin efflux substrate increased fertility under drought and salt stress. These data indicate that NO homeostasis is critical to normal auxin transport and maternal control of FG development, which in turn determine seed yield. Understanding this aspect of fertility control could contribute to mediating yield loss under adverse conditions.

    

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