Juan Manuel Peralta

Arsenate [As(V)] competes with phosphate for uptake, creating a challenge for peanut production in P-limited, As-affected agricultural systems. We investigated whether phosphate-solubilizing plant growth-promoting bacteria (PS-PGPB) with contrasting As(V)-tolerance phenotypes remained functional and benefited peanut when coinoculated with Bradyrhizobium sp. SEMIA6144. We screened four PS strains: native Enterobacter sp. J49, Serratia sp. S119, and Serratia sp. J260; and commercial Pseudomonas pergaminensis PMT1. J49 and PMT1 tolerated millimolar As(V), whereas S119 and J260 were inhibited at micromolar concentrations. As(V) increased soluble P in J49 and PMT1, maintained it in S119, and decreased it in J260. In J49 and S119, As(V) increased arsenate reductase and superoxide dismutase activities, but only S119 showed lipid peroxidation and induced glutathione-related enzymes, revealing different redox responses under strain-specific exposure conditions. Despite this divergence, both strains converged in planta. At a regionally relevant 3 µM As(V), coinoculation with either strain increased shoot P concentration in tricalcium phosphate (PTC)-supplied plants relative to PTC alone and restricted shoot As to below the method detection limit without significantly reducing root As concentrations. Nevertheless, As accumulated in nodules with J49 but remained undetected with S119. These findings identify integrated strain–plant–rhizobium performance as a key criterion for selecting inoculants that couple P acquisition with restriction of detectable total As translocation to shoots.

Summary: Root hairs (RH) are excellent model systems for studying cell size and polarity since they elongate several hundred‐fold their original size. Their tip growth is determined both by intrinsic and environmental signals. Although nutrient availability and temperature are key factors for a sustained plant growth, the molecular mechanisms underlying their sensing and downstream signaling pathways remain unclear. We use genetics to address the roles of the cell surface receptor kinase FERONIA (FER) and the nutrient sensing TOR Complex 1 (TORC) in RH growth. We identified that low temperature (10°C) triggers a strong RH elongation response in Arabidopsis thaliana involving FER and TORC. We found that FER is required to perceive limited nutrient availability caused by low temperature. FERONIA interacts with and activates TORC‐downstream components to trigger RH growth. In addition, the small GTPase Rho of plants 2 (ROP2) is also involved in this RH growth response linking FER and TOR. We also found that limited nitrogen nutrient availability can mimic the RH growth response at 10°C in a NRT1.1‐dependent manner. These results uncover a molecular mechanism by which a central hub composed by FER‐ROP2‐TORC is involved in the control of RH elongation under low temperature and nitrogen deficiency.

Root hair cells are important sensors of soil conditions. They grow towards and absorb water-soluble nutrients. This fast and oscillatory growth is mediated by continuous remodeling of the cell wall. Root hair cell walls contain polysaccharides and hydroxyproline-rich glycoproteins, including extensins (EXTs). Class-III peroxidases (PRXs) are secreted into the apoplastic space and are thought to trigger either cell wall loosening or polymerization of cell wall components, such as Tyr-mediated assembly of EXT networks (EXT-PRXs). The precise role of these EXT-PRXs is unknown. Using genetic, biochemical, and modeling approaches, we identified and characterized three root-hair-specific putative EXT-PRXs, PRX01, PRX44, and PRX73. prx01,44,73 triple mutation and PRX44 and PRX73 overexpression had opposite effects on root hair growth, peroxidase activity, and ROS production, with a clear impact on cell wall thickness. We use an EXT fluorescent reporter with contrasting levels of cell wall insolubilization in prx01,44,73 and PRX44-overexpressing background plants. In this study, we propose that PRX01, PRX44, and PRX73 control EXT-mediated cell wall properties during polar expansion of root hair cells.

Root Hairs (RHs) growth is influenced by endogenous and by external environmental signals that coordinately regulate its final cell size. We have recently determined that RH growth was unexpectedly boosted whenArabidopsis thalianaseedlings are cultivated at low temperatures. It was proposed that RH growth plasticity in response to low temperature was linked to a reduced nutrient availability in the media. Here, we explore the molecular basis of this RH growth response by using a Genome Wide Association Study (GWAS) approach usingArabidopsis thaliananatural accessions. We identify the poorly characterized PEROXIDASE 62 (PRX62) and a related protein PRX69 as key proteins under moderate low temperature stress. Strikingly, a cell wall protein extensin (EXT) reporter reveals the effect of peroxidase activity on EXT cell wall association at 10 °C in the RH apical zone. Collectively, our results indicate that PRX62, and to a lesser extent PRX69, are key apoplastic PRXs that modulate ROS-homeostasis and cell wall EXT-insolubilization linked to RH elongation at low temperature.

Root hairs (RH) are excellent model systems for studying cell size and polarity since they elongate several hundred-fold their original size. Their tip growth is determined both by intrinsic and environmental signals. Although nutrient availability and temperature are key factors for a sustained plant growth, the molecular mechanisms underlying their sensing and downstream signaling pathways remain unclear. Here, we identified that low temperature (10°C) triggers a strong RH elongation response involving the cell surface receptor kinase FERONIA (FER) and the nutrient sensing TOR Complex 1 (TORC). In this study, we found that FER is required to perceive limited nutrient availability caused by low temperature. FER interacts with and activates TORC downstream components to trigger RH growth. In addition, the small GTPase Rho-related protein from plants 2 (ROP2) is also involved in this RH growth response linking FER and TOR. We also found that limited nitrogen nutrient availability can mimic the RH growth response at 10°C in a NRT1.1-dependent manner. These results uncover a molecular mechanism by which a central hub composed by FER-ROP2-TORC is involved in the control of RH elongation under low temperature and nitrogen deficiency.

Arsenic in groundwater constitutes an agronomic problem due to its potential accumulation in the food chain. Among the agro‐sustainable tools to reduce metal(oid)s toxicity, the use of plant growth‐promoting bacteria (PGPB) becomes important. For that, and based on previous results in which significant differences of As translocation were observed when inoculating maize plants with Az39 or CD Azospirillum strains, we decided to decipher the redox metabolism changes and the antioxidant system response of maize plants inoculated when exposed to a realistic arsenate (As^V) dose. Results showed that As^V caused morphological changes in the root exodermis. Photosynthetic pigments decreased only in CD inoculated plants, while oxidative stress evidence was detected throughout the plant, regardless of the assayed strain. The antioxidant response was strain‐differential since only CD inoculated plants showed an increase in superoxide dismutase, glutathione S‐transferase (GST), and glutathione reductase (GR) activities while other enzymes showed the same behavior irrespective of the inoculated strain. Gene expression assays reported that only GST23 transcript level was upregulated by arsenate, regardless of the inoculated strain. As^V diminished the glutathione (GSH) content of roots inoculated with the Az39 strain, and CD inoculated plants showed a decrease of oxidized GSH (GSSG) levels. We suggest a model in which the antioxidant response of the maize‐diazotrophs system is modulated by the strain and that GSH plays a central role acting mainly as a substrate for GST. These findings generate knowledge for a suitable PGPB selection, and its scaling to an effective bioinoculant formulation for maize crops exposed to adverse environmental conditions.