No abstract

Molecular, genetic, and electrophysiological evidence indicates that at least one of the plant Glu receptor-like molecules, GLR3.4, functions as an amino acid-gated Ca 2+ channel at the plasma membrane. The aspect of plant physiology, growth, or development to which GLR3.4 contributes is an open question. Protein localization studies performed here provide important information. In roots, GLR3.4 and the related GLR3.2 protein were present primarily in the phloem, especially in the vicinity of the sieve plates. GLR3.3 was expressed in most cells of the growing primary root but was not enriched in the phloem, including the sieve plate area. GLR3.2 and GLR3.4 physically interacted with each other better than with themselves as evidenced by a biophotonic assay performed in human embryonic kidney cells and Nicotiana benthamiana leaf cells. GLR3.3 interacted poorly with itself or the other two GLRs. Mutations in GLR3.2, GLR3.4, or GLR3.2 and GLR3.4 caused the same and equally severe phenotype, namely, a large overproduction and aberrant placement of lateral root primordia. Loss of GLR3.3 did not affect lateral root primordia. These results support the hypothesis that apoplastic amino acids acting through heteromeric GLR3.2/GLR3.4 channels affect lateral root development via Ca 2+ signaling in the phloem.

A cDNA was isolated from soybean (Glycine max) nodules that encodes a putative transporter (GmN70) of the major facilitator superfamily. GmN70 is expressed predominantly in mature nitrogen-fixing root nodules. By western-blot and immunocytochemical analyses, GmN70 was localized to the symbiosome membrane of infected root nodule cells, suggesting a transport role in symbiosis. To investigate its transport function, cRNA encoding GmN70 was expressed in Xenopus laevis oocytes, and two-electrode voltage clamp analysis was performed. Ooctyes expressing GmN70 showed outward currents that are carried by anions with a selectivity of nitrate > nitrite ≫ chloride. These currents showed little sensitivity to pH or the nature of the counter cation in the oocyte bath solution. One-half maximal currents were induced by nitrate concentrations between 1 to 3 mm. No apparent transport of organic anions was observed. Voltage clamp records of an ortholog of GmN70 from Lotus japonicus (LjN70; K. Szczyglowski, P. Kapranov, D. Hamburger, F.J. de Bruijn [1998] Plant Mol Biol 37: 651–661) also showed anion currents with a similar selectivity profile. Overall, these findings suggest that GmN70 and LjN70 are inorganic anion transporters of the symbiosome membrane with enhanced preference for nitrate. These transport activities may aid in regulation of ion and membrane potential homeostasis, possibly in response to external nitrate concentrations that are known to regulate the symbiosis.

Beet curly top virus (BCTV) significantly reduces sugar beet yield in semi-arid production areas. Genetic resistance to BCTV is limited; therefore, identification of additional resistance-associated factors is highly desired. Using 16S rRNA sequencing and BCTV resistant (R) genotypes (KDH13, KDH4-9) along with a susceptible (S) genotype (KDH19-17), we investigated leaf bacteriome changes during BCTV post inoculation (pi). At day 6 (~6-week-old plants), Cyanobacteria were predominant (~90%); whereas, at week 4 (~10-week-old plants) Firmicutes (11–66%), Bacteroidetes (17–26%), and Verrucomicrobia (12–29%) were predominant phyla and genotype dependent. Both Bacteroidetes and Verrucomicrobia, increased post infection only in the R lines. The bacterial genera Brevibacillus increased at 6 dpi, and Akkermansia and Bacteroides at 4 wkpi in the R lines. Linear discriminant analysis effect size (LEfSe) identified potential biomarkers in the R vs. S lines. Functional profiling revealed bacterial enrichment associated with the TCA cycle, polyisoprenoid, and L-methionine biosynthesis pathways only in KDH4-9 at 6 dpi. At 4 wkpi, bacteria associated with tryptophan and palmitate biosynthesis in the R lines, and uridine monophosphate, phosphatidyl glycerol, and phospholipid biosynthesis in the S line, were enriched. Future characterization of bacterial genera with antiviral properties will help establish their use as biocontrol agents/biomarkers against BCTV.