Ethylene controls three-dimensional growth involving reduced auxin levels in the moss Physcomitrium patens.

The conquest of land by plants was concomitant with, and possibly enabled by, the evolution of three-dimensional (3D) growth. The moss Physcomitrium patens provides a model system for elucidating molecular mechanisms in the initiation of 3D growth. Here, we investigate whether the phytohormone ethylene, which is believed to have been a signal before land plant emergence, plays a role in 3D growth regulation in P. patens. We report ethylene controls 3D gametophore formation, based on results from exogenously applied ethylene and genetic manipulation of PpEIN2, which is a central component in the ethylene signaling pathway. Overexpression (OE) of PpEIN2 activates ethylene responses and leads to earlier formation of gametophores with fewer gametophores produced thereafter, phenocopying ethylene-treated wild-type. Conversely, Ppein2 knockout mutants, which are ethylene insensitive, show initially delayed gametophore formation with more gametophores produced later. Furthermore, pharmacological and biochemical analyses reveal auxin levels are decreased in the OE lines but increased in the knockout mutants. Our results suggest that evolutionarily, ethylene and auxin molecular networks were recruited to build the plant body plan in ancestral land plants. This might have played a role in enabling ancient plants to acclimate to the continental surfaces of the planet.

Development of PEG-mediated genetic transformation and gene editing system of Bryum argenteum as an abiotic stress tolerance model plant.

KEY MESSAGE: To establish a sterile culture system and protoplast regeneration system for Bryum argenteum, and to establish and apply CRISPR/Cas9 system in Bryum argenteum. Bryum argenteum is a fascinating, cosmopolitan, and versatile moss species that thrives in various disturbed environments. Because of its comprehensive tolerance to the desiccation, high UV and extreme temperatures, it is emerging as a model moss for studying the molecular mechanisms underlying plant responses to abiotic stresses. However, the lack of basic tools such as gene transformation and targeted genome modification has hindered the understanding of the molecular mechanisms underlying the survival of B. argenteum in different environments. Here, we reported the protonema of B. argenteum can survive up to 95.4% water loss. In addition, the genome size of B. argenteum is approximately 313 Mb by kmer analysis, which is smaller than the previously reported 700 Mb. We also developed a simple method for protonema induction and an efficient protoplast isolation and regeneration protocol for B. argenteum. Furthermore, we established a PEG-mediated protoplast transient transfection and stable transformation system for B. argenteum. Two homologues of ABI3(ABA-INSENSITIVE 3) gene were successfully cloned from B. argenteum. To further investigate the function of the ABI3 gene in B. argenteum, we used the CRISPR/Cas9 genetic editing system to target the BaABI3A and BaABI3B gene in B. argenteum protoplasts. This resulted in mutagenesis at the target in about 2-5% of the regenerated plants. The isolated abi3a and abi3b mutants exhibited increased sensitivity to desiccation, suggesting that BaABI3A and BaABI3B play redundant roles in desiccation stress. Overall, our results provide a rapid and simple approach for molecular genetics in B. argenteum. This study contributes to a better understanding of the molecular mechanisms of plant adaptation to extreme environmental.

Structural insights into a unique PSI-LHCI-LHCII-Lhcb9 supercomplex from moss Physcomitrium patens.

Photosystem I (PSI) possesses a variable supramolecular organization among different photosynthetic organisms to adapt to different light environments. Mosses are evolutionary intermediates that diverged from aquatic green algae and evolved into land plants. The moss Physcomitrium patens (P. patens) has a light-harvesting complex (LHC) superfamily more diverse than those of green algae and higher plants. Here, we solved the structure of a PSI-LHCI-LHCII-Lhcb9 supercomplex from P. patens at 2.68 Å resolution using cryo-electron microscopy. This supercomplex contains one PSI-LHCI, one phosphorylated LHCII trimer, one moss-specific LHC protein, Lhcb9, and one additional LHCI belt with four Lhca subunits. The complete structure of PsaO was observed in the PSI core. One Lhcbm2 in the LHCII trimer interacts with PSI core through its phosphorylated N terminus, and Lhcb9 mediates assembly of the whole supercomplex. The complicated pigment arrangement provided important information for possible energy-transfer pathways from the peripheral antennae to the PSI core.

Evaluation the effectiveness of the Jiangniaosuan formulation in the treatment of hyperuricemic nephropathy in patients with chronic kidney disease stages 3-4: Study protocol of a randomized controlled trial.

Background: Hyperuricemic nephropathy is a highly prevalent kidney disease induced by excessive accumulation and deposition of monosodium urate in kidney, which contributes to the loss of kidney function. The Jiangniaosuan formulation (JNSF) is a Chinese herbal medicine treatment. The aim of this study is to evaluate its efficacy and safety among patients with hyperuricemic nephropathy at chronic kidney disease (CKD) stages 3-4 and with obstruction of phlegm turbidity and blood stasis syndrome. Methods: Our research is designed as a single-centre, double-blinded, randomized, placebo-controlled trial for 118 patients diagnosed with hyperuricemic nephropathy at CKD stages 3-4 and with obstruction of phlegm turbidity and blood stasis syndrome in mainland China. Patients are to be randomized into two groups: either the intervention group which receives JNSF 20.4 g/day combined with febuxostat 20-40 mg/day, or the control group which receives JNSF placebo 20.4 g/day combined with febuxostat 20-40 mg/day. The intervention will be carried on for 24 weeks. The change in estimated glomerular filtration rate (eGFR) is set as the primary outcome. Secondary outcomes include changes in serum uric acid, serum nitric oxide, urinary albumin/creatinine ratio, urinary N-acetyl-ß-D glucosaminidase, urinary ß2 microglobulin, urinary retinol binding protein and TCM syndromes in 24 weeks. Statistical analysis will be formulated by SPSS 24.0. Discussion: The trial will conduce to the comprehensive assessment in the efficacy and safety of JNSF among patients diagnosed with hyperuricemic nephropathy at CKD stages 3-4, and provide a clinical method available on systems of the combination of modern medicine and TCM.

A glutamate receptor-like gene is involved in ABA-mediated growth control in Physcomitrium (Physcomitrella) patens.

Plant glutamate receptor homologs (GLRs), which function as key calcium channels, play pivotal roles in various developmental processes as well as stress responses. The moss Physcomitrium patens, a representative of the earliest land plant lineage, possess multiple pathways of hormone signaling for coordinating growth and adaptation responses. However, it is not clear whether GLRs are connected to hormone-mediated growth control in the moss. In this study, we report that one of the two GLRs in P. patens, PpGLR1, involves in abscisic acid (ABA)-mediated growth regulation. ABA represses the growth of wild-type moss, and intriguingly, the PpGLR1 transcript levels are significantly increased in response to ABA treatment, based on both gene expression and the PpGLR1pro::GUS reporter results. Furthermore, the growth of Ppglr1 knockout moss mutants is hypersensitive to ABA treatment. These results suggest that PpGLR1 plays a critical role in ABA-mediated growth regulation, which provide useful information for our further investigation of the regulatory mechanism between Ca2+ signal and ABA in moss growth control.

TEB/POLQ plays dual roles in protecting Arabidopsis from NO-induced DNA damage.

Nitric oxide (NO) is a key player in numerous physiological processes. Excessive NO induces DNA damage, but how plants respond to this damage remains unclear. We screened and identified an Arabidopsis NO hypersensitive mutant and found it to be allelic to TEBICHI/POLQ, encoding DNA polymerase θ. The teb mutant plants were preferentially sensitive to NO- and its derivative peroxynitrite-induced DNA damage and subsequent double-strand breaks (DSBs). Inactivation of TEB caused the accumulation of spontaneous DSBs largely attributed to endogenous NO and was synergistic to DSB repair pathway mutations with respect to growth. These effects were manifested in the presence of NO-inducing agents and relieved by NO scavengers. NO induced G2/M cell cycle arrest in the teb mutant, indicative of stalled replication forks. Genetic analyses indicate that Polθ is required for translesion DNA synthesis across NO-induced lesions, but not oxidation-induced lesions. Whole-genome sequencing revealed that Polθ bypasses NO-induced base adducts in an error-free manner and generates mutations characteristic of Polθ-mediated end joining. Our experimental data collectively suggests that Polθ plays dual roles in protecting plants from NO-induced DNA damage. Since Polθ is conserved in higher eukaryotes, mammalian Polθ may also be required for balancing NO physiological signaling and genotoxicity.

Effect of Baihu and Guizhi decoction in acute gouty arthritis: study protocol for a randomized controlled trial.

BACKGROUND: The prevalence rates of gout worldwide have increased annually. Acute gouty arthritis (AGA) accounts for a large proportion of gout patients and causes severe physical and mental pain in patients. Controlling the occurrence and development of gout inflammation is the first step in the treatment of gout. The main treatment drugs in gout are non-steroid anti-inflammatory drugs (NSAIDs), colchicine, and glucocorticoids, but these treatments have many adverse reactions which limit their clinical application. Baihu and Guizhi decoction (BHGZ) is one of the classic prescriptions in the Synopsis of the Golden Chamber and is a good prescription for AGA. Previous clinical studies have shown that BHGZ confers a strong benefit for treating AGA. However, the literature shows a lack of high-quality RCT research on BHGZ with respect to AGA. Therefore, in this study, we use a randomized, double-blind, controlled study with a placebo to evaluate the clinical efficacy and safety of BHGZ on the AGA of moist heat arthralgia spasm syndrome. METHODS: This study is a randomized, double-blind, controlled clinical trial. A total of 102 adult participants with AGA of moist heat arthralgia spasm syndrome will be enrolled, with balanced treatment allocation (1:1). The experimental intervention will be BHGZ plus the low-dose colchicine, and the control intervention will be placebo plus the low-dose colchicine for 10 days. To study the clinical efficacy (including VAS score; joint tenderness, joint swelling, joint movement disorder; TCM evidence efficacy score) and the changes of inflammatory indexes. At the same time, the improvement of joint inflammation in patients with AGA will be observed from musculoskeletal ultrasound imaging, and the safety evaluation will be carried out. DISCUSSION: This study will be the first placebo-controlled RCT to assess whether BHGZ plus low-dose colchicine have beneficial effects on changing reducing inflammation of joints for patients with AGA of moist heat arthralgia spasm syndrome. The results of this trial will help to provide evidence-based recommendations for clinicians. TRIAL REGISTRATION: Chinese Clinical Trials Register ChiCTR1900024974 . Registered on 5 August 2019.

ADH2/GSNOR1 is a key player in limiting genotoxic damage mediated by formaldehyde and UV-B in Arabidopsis.

Maintenance of genome stability is an essential requirement for all living organisms. Formaldehyde and UV-B irradiation cause DNA damage and affect genome stability, growth and development, but the interplay between these two genotoxic factors is poorly understood in plants. We show that Arabidopsis adh2/gsnor1 mutant, which lacks alcohol dehydrogenase 2/S-nitrosoglutathione reductase 1 (ADH2/GSNOR1), are hypersensitive to low fluence UV-B irradiation or UV-B irradiation-mimetic chemicals. Although the ADH2/GSNOR1 enzyme can act on different substrates, notably on S-hydroxymethylglutathione (HMG) and S-nitrosoglutathione (GSNO), our study provides several lines of evidence that the sensitivity of gsnor1 to UV-B is caused mainly by UV-B-induced formaldehyde accumulation rather than other factors such as alteration of the GSNO concentration. Our results demonstrate an interplay between formaldehyde and UV-B that exacerbates genome instability, leading to severe DNA damage and impaired growth and development in Arabidopsis, and show that ADH2/GSNOR1 is a key player in combating these effects.

Residue 49 of AtMinD1 Plays a Key Role in the Guidance of Chloroplast Division by Regulating the ARC6-AtMinD1 Interaction.

Chloroplasts evolved from a free-living cyanobacterium through endosymbiosis. Similar to bacterial cell division, chloroplasts replicate by binary fission, which is controlled by the Minicell (Min) system through confining FtsZ ring formation at the mid-chloroplast division site. MinD, one of the most important members of the Min system, regulates the placement of the division site in plants and works cooperatively with MinE, ARC3, and MCD1. The loss of MinD function results in the asymmetric division of chloroplasts. In this study, we isolated one large dumbbell-shaped and asymmetric division chloroplast Arabidopsis mutant Chloroplast Division Mutant 75 (cdm75) that contains a missense mutation, changing the arginine at residue 49 to a histidine (R49H), and this mutant point is located in the N-terminal Conserved Terrestrial Sequence (NCTS) motif of AtMinD1, which is only typically found in terrestrial plants. This study provides sufficient evidence to prove that residues 1-49 of AtMinD1 are transferred into the chloroplast, and that the R49H mutation does not affect the function of the AtMinD1 chloroplast transit peptide. Subsequently, we showed that the point mutation of R49H could remove the punctate structure caused by residues 1-62 of the AtMinD1 sequence in the chloroplast, suggesting that the arginine in residue 49 (Arg49) is essential for localizing the punctate structure of AtMinD11 - 62 on the chloroplast envelope. Unexpectedly, we found that AtMinD1 could interact directly with ARC6, and that the R49H mutation could prevent not only the previously observed interaction between AtMinD1 and MCD1 but also the interaction between AtMinD1 and ARC6. Thus, we believe that these results show that the AtMinD1 NCTS motif is required for their protein interaction. Collectively, our results show that AtMinD1 can guide the placement of the division site to the mid chloroplast through its direct interaction with ARC6 and reveal the important role of AtMinD1 in regulating the AtMinD1-ARC6 interaction.

Observation of the curative effect of Guizhi-Shaoyao-Zhimu decoction combined with methotrexate in the treatment of early rheumatoid arthritis based on ultrasonic evaluation: study protocol of a randomized, double-blind, controlled clinical trial.

BACKGROUND: Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease with the primary clinical symptoms of joint swelling and pain. Early detection of erosion and synovial inflammation at an active stage resulting from RA can prevent damage to the joints and activity restriction. However, there are still many patients who do not respond to these treatments; the development of newer, safer drugs is urgently needed. Compared to Western medicine, Guizhi-Shaoyao-Zhimu decoction has equal or higher efficacy and safety for RA patients. With the widespread use of musculoskeletal ultrasound (MSUS), this technology holds great value for the degree of joint damage in RA patients, guiding the clinical selection of treatments, and assessing of prognosis. Therefore, we designed a double-blinded randomized controlled clinical trial to measure the safety and efficacy of Guizhi-Shaoyao-Zhimu decoction in treating early-stage RA using MSUS. METHODS: This study is a randomized, double-blinded, parallel group, placebo-controlled trial. A total of 152 adult participants with early RA will be enrolled, with balanced treatment allocation (1:1). The experimental intervention will be Guizhi-Shaoyao-Zhimu decoction plus the conventional medicine methotrexate and the control intervention will be placebo plus the conventional drug methotrexate for 3 months. In addition, both groups will receive folic acid during treatment to prevent side effects from methotrexate. The primary outcomes are the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), hepatic and renal function, visual analog scale, disease activity score in 28 joints, measurement scale for TCM symptoms, and 7-joint ultrasound score. DISCUSSION: We designed this double-blinded randomized controlled clinical trial to evaluate the efficacy and safety of Guizhi-Shaoyao-Zhimu decoction in RA patients using MSUS. The results of this trial may provide insights into how to improve the clinical symptoms of RA patients and delay further joint destruction. We hope that this trial may provide preliminary evidence of the efficacy of Guizhi-Shaoyao-Zhimu decoction in treating RA patients and that these results aid researchers, practitioners, and patients alike. AIM: The main aim of the study is to clarify the efficacy and safety of Guizhi-Shaoyao-Zhimu decoction in patients with early RA. TRIAL REGISTRATION: Chinese Clinical Trials Register ChiCTR2000036141 . Registered on 21 August 2020 (retroactively registered).

A chloride efflux transporter, BIG RICE GRAIN 1, is involved in mediating grain size and salt tolerance in rice.

Grain size is determined by the size and number of cells in the grain. The regulation of grain size is crucial for improving crop yield; however, the genes and molecular mechanisms that control grain size remain elusive. Here, we report that a member of the detoxification efflux carrier /Multidrug and Toxic Compound Extrusion (DTX/MATE) family transporters, BIG RICE GRAIN 1 (BIRG1), negatively influences grain size in rice (Oryza sativa L.). BIRG1 is highly expressed in reproductive organs and roots. In birg1 grain, the outer parenchyma layer cells of spikelet hulls are larger than in wild-type (WT) grains, but the cell number is unaltered. When expressed in Xenopus laevis oocytes, BIRG1 exhibits chloride efflux activity. Consistent with this role of BIRG1, the birg1 mutant shows reduced tolerance to salt stress at a toxic chloride level. Moreover, grains from birg1 plants contain a higher level of chloride than those of WT plants when grown under normal paddy field conditions, and the roots of birg1 accumulate more chloride than those of WT under saline conditions. Collectively, the data suggest that BIRG1 in rice functions as a chloride efflux transporter that is involved in mediating grain size and salt tolerance by controlling chloride homeostasis.

A transceptor-channel complex couples nitrate sensing to calcium signaling in Arabidopsis.

Nitrate-induced Ca2+ signaling is crucial for the primary nitrate response in plants. However, the molecular mechanism underlying the generation of the nitrate-specific calcium signature remains unknown. We report here that a cyclic nucleotide-gated channel (CNGC) protein, CNGC15, and the nitrate transceptor (NRT1.1) constitute a molecular switch that controls calcium influx depending on nitrate levels. The expression of CNGC15 is induced by nitrate, and its protein is localized at the plasma membrane after establishment of young seedlings. We found that disruption of CNGC15 results in the loss of the nitrate-induced Ca2+ signature (primary nitrate response) and retards root growth, reminiscent of the phenotype observed in the nrt1.1 mutant. We further showed that CNGC15 is an active Ca2+-permeable channel that physically interacts with the NRT1.1 protein in the plasma membrane. Importantly, we discovered that CNGC15-NRT1.1 interaction silences the channel activity of the heterocomplex, which dissociates upon a rise in nitrate levels, leading to reactivation of the CNGC15 channel. The dynamic interactions between CNGC15 and NRT1.1 therefore control the channel activity and Ca2+ influx in a nitrate-dependent manner. Our study reveals a new nutrient-sensing mechanism that utilizes a nutrient transceptor-channel complex assembly to couple nutrient status to a specific Ca2+ signature.

Antenna arrangement and energy-transfer pathways of PSI-LHCI from the moss Physcomitrella patens.

Plants harvest light energy utilized for photosynthesis by light-harvesting complex I and II (LHCI and LHCII) surrounding photosystem I and II (PSI and PSII), respectively. During the evolution of green plants, moss is at an evolutionarily intermediate position from aquatic photosynthetic organisms to land plants, being the first photosynthetic organisms that landed. Here, we report the structure of the PSI-LHCI supercomplex from the moss Physcomitrella patens (Pp) at 3.23 Å resolution solved by cryo-electron microscopy. Our structure revealed that four Lhca subunits are associated with the PSI core in an order of Lhca1-Lhca5-Lhca2-Lhca3. This number is much decreased from 8 to 10, the number of subunits in most green algal PSI-LHCI, but the same as those of land plants. Although Pp PSI-LHCI has a similar structure as PSI-LHCI of land plants, it has Lhca5, instead of Lhca4, in the second position of Lhca, and several differences were found in the arrangement of chlorophylls among green algal, moss, and land plant PSI-LHCI. One chlorophyll, PsaF-Chl 305, which is found in the moss PSI-LHCI, is located at the gap region between the two middle Lhca subunits and the PSI core, and therefore may make the excitation energy transfer from LHCI to the core more efficient than that of land plants. On the other hand, energy-transfer paths at the two side Lhca subunits are relatively conserved. These results provide a structural basis for unravelling the mechanisms of light-energy harvesting and transfer in the moss PSI-LHCI, as well as important clues on the changes of PSI-LHCI after landing.

Structural basis for plant lutein biosynthesis from α-carotene.

Two cytochrome P450 enzymes, CYP97A3 and CYP97C1, catalyze hydroxylations of the ß- and ε-rings of α-carotene to produce lutein. Chirality is introduced at the C-3 atom of both rings, and the reactions are both pro-3R-stereospecific. We determined the crystal structures of CYP97A3 in substrate-free and complex forms with a nonnatural substrate and the structure of CYP97C1 in a detergent-bound form. The structures of CYP97A3 in different states show the substrate channel and the structure of CYP97C1 bound with octylthioglucoside confirms the binding site for the carotenoid substrate. Biochemical assays confirm that the ferredoxin-NADP+ reductase (FNR)-ferredoxin pair is used as the redox partner. Details of the pro-3R stereospecificity are revealed in the retinal-bound CYP97A3 structure. Further analysis indicates that the CYP97B clan bears similarity to the ß-ring-specific CYP97A clan. Overall, our research describes the molecular basis for the last steps of lutein biosynthesis.

Molecular cloning and functional characterization of Physcomitrella patens UBC13-UEV1 genes required for Lys63-linked polyubiquitination.

Ubc13 and Ubc/E2 variant (Uev) form a stable heterodimer to mediate Lys63-linked polyubiquitination. Unicellular eukaryotic genomes often contain single UBC13 and UEV gene; however, multiple homologs were found in higher plants. As initial land plants, Physcomitrella patens occupies a key evolutionary position between green algae and higher plants. In this study, we report the identification and functional characterization of two UBC13 and three UEV1 genes from P. patens. Both PpUbc13s form heterodimers with PpUev1B or PpUev1C, which catalyze Lys63-linked polyubiquitination in vitro and functionally complement the yeast ubc13 mms2 null mutant from killing by DNA-damaging agents. In contrast, PpUev1A is unable to interact with Ubc13s and cannot complement the yeast mms2 mutant. Two single mutations, PpUev1A-D12N and ΔCT, barely have any effect; however, the corresponding double mutation makes PpUev1A functional in both heterodimer formation and complementation. This study identifies a critical Uev residue located in the Ubc13-Uev interface and reveals that mosses began to evolve multiple UBC13 and UEV orthologs in order to adapt to the terrestrial environment. The evolutionary significance of PpUEV1A is discussed.

PpAKR1A, a Novel Aldo-Keto Reductase from Physcomitrella Patens, Plays a Positive Role in Salt Stress.

The moss Physcomitrella patens is tolerant of highly saline environments. In plants, salinity stress may induce the production of toxic reactive carbonyl species (RCS) and oxidative damage. Aldo-keto reductases (AKRs) are a large group of NADP-dependent oxidoreductases involved in RCS detoxification. However, many members in this superfamily remain uncharacterized. In this study, we cloned and characterised a putative AKR1 from P. patens, named PpAKR1A. Notably, the transcription level of PpAKR1A was induced by salt and methylglyoxal (MG) stress, and the recombinant PpAKR1A protein catalysed the reduction of toxic aldehydes. PpAKR1A knockout mutants of P. patens (ppakr1a) were sensitive to NaCl and MG treatment, as indicated by much lower concentrations of chlorophyll and much higher concentrations of MG and H2O2 than those in WT plants. Meanwhile, ppakr1a plants exhibited decreases in the MG-reducing activity and reactive oxygen species-scavenging ability in response to salt stress, possibly due to decreases in the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Our results indicate that PpAKR1A is an aldo-keto reductase that detoxifies MG and thus plays an important role in salt stress tolerance in P. patens.

Regulatory Mechanism of ABA and ABI3 on Vegetative Development in the Moss Physcomitrella patens.

The moss Physcomitrella patens is a model system for studying plant developmental processes. ABSCISIC ACID INSENSITIVE3 (ABI3), a transcription factor of the ABA signaling pathway, plays an important role in plant growth and development in vascular plant. To understand the regulatory mechanism of ABA and PpABI3 on vegetative development in Physcomitrella patens, we applied physiological, cellular, and RNA-seq analyses in wild type (WT) plants and ∆abi3 mutants. During ABA treatment, the growth of gametophytes was inhibited to a lesser extent ∆abi3 plants compared with WT plants. Microscopic observation indicated that the differentiation of caulonemata from chloronemata was accelerated in ∆abi3 plants when compared with WT plants, with or without 10 µM of ABA treatment. Under normal conditions, auxin concentration in ∆abi3 plants was markedly higher than that in WT plants. The auxin induced later differentiation of caulonemata from chloronemata, and the phenotype of ∆abi3 plants was similar to that of WT plants treated with exogenous indole-3-acetic acid (IAA). RNA-seq analysis showed that the PpABI3-regulated genes overlapped with genes regulated by the ABA treatment, and about 78% of auxin-related genes regulated by the ABA treatment overlapped with those regulated by PpABI3. These results suggested that ABA affected vegetative development partly through PpABI3 regulation in P. patens; PpABI3 is a negative regulator of vegetative development in P. patens, and the vegetative development regulation by ABA and PpABI3 might occur by regulating the expression of auxin-related genes. PpABI3 might be associated with cross-talk between ABA and auxin in P. patens.

Corrigendum: Physcomitrella Patens Dehydrins (PpDHNA and PpDHNC) Confer Salinity and Drought Tolerance to Transgenic Arabidopsis Plants.

[This corrects the article on p. 1316 in vol. 8, PMID: 28798765.].

Desiccation tolerance in Physcomitrella patens: Rate of dehydration and the involvement of endogenous abscisic acid (ABA).

The moss Physcomitrella patens, a model system for basal land plants, tolerates several abiotic stresses, including dehydration. We previously reported that Physcomitrella patens survives equilibrium dehydration to -13 MPa in a closed system at 91% RH. Tolerance of desiccation to water potentials below -100 MPa was only achieved by pretreatment with exogenous abscisic acid (ABA). We report here that gametophores, but not protonemata, can survive desiccation below -100 MPa after a gradual drying regime in an open system, without exogenous ABA. In contrast, faster equilibrium drying at 90% RH for 3-5 days did not induce desiccation tolerance in either tissue. Endogenous ABA accumulated in protonemata and gametophores under both drying regimes, so did not correlate directly with desiccation tolerance. Gametophores of a Ppabi3a/b/c triple knock out transgenic line also survived the gradual dehydration regime, despite impaired ABA signaling. Our results suggest that the initial drying rate, and not the amount of endogenous ABA, may be critical in the acquisition of desiccation tolerance. Results from this work will provide insight into ongoing studies to uncover the role of ABA in the dehydration response and the underlying mechanisms of desiccation tolerance in this bryophyte.