Localization of XopN_KXO85, OsVOZ2, and OsXNP in plant cells.

<p>Subcellular localization of the XopN_KXO85-GFP, OsVOZ2-GFP, and OsXNP-GFP fusion proteins in maize mesophyll cells. OsABF1-RFP was used as a nuclear marker. GFP (green) fluorescence was merged with RFP (red) fluorescence. Bars = 10 µm.</p

Identification of Fatty Acid Glucose Esters as Os9BGlu31 Transglucosidase Substrates in Rice Flag Leaves

Rice Os9BGlu31 transglucosidase transfers glucosyl moieties between various carboxylic acids and alcohols, including phenolic acids and flavonoids, in vitro. The role of Os9BGlu31 transglucosidase in rice plant metabolism has only been suggested to date. Methanolic extracts of rice bran and leaves were found to contain oleic acid and linoleic acid to which Os9BGlu31 could transfer glucose from the 4-nitrophenyl β-d-glucoside (4NPGlc) donor to form 1-<i>O</i>-acyl glucose esters. Os9BGlu31 showed higher activity with oleic acid (18:1) and linoleic acid (18:2) than with stearic acid (18:0) and had both a higher <i>k</i>_cat and a higher <i>K</i>_m for linoleic than oleic acid in the presence of 8 mM 4NPGlc donor. <i>Os9BGlu31</i> knockout mutant rice lines were found to have significantly larger amounts of fatty acid glucose esters than wild-type control lines. Because the transglucosylation reaction is reversible, these data suggest that fatty acid glucose esters act as glucosyl donor substrates for Os9BGlu31 transglucosidase in rice

Pathogenicity test for <i>xop</i> mutants of <i>Xoo</i> KXO85 in rice.

<p><b>A</b>. Disease severity of each <i>xop</i> mutant in 3-month-old rice leaves. W, water; 85, wild-type KXO85; Q, KXO85 <i>xopQ</i>_<i>KXO85</i>::EZ-Tn<i>5</i>; X, KXO85 <i>xopX</i>_<i>KXO85</i>::EZ-Tn<i>5</i>; P1, KXO85 <i>xopP1</i>_<i>KXO85</i>::EZ-Tn<i>5</i>; P2, KXO85 <i>xopP2</i>_<i>KXO85</i>::EZ-Tn<i>5</i>; N, KXO85 <i>xopN</i>_<i>KXO85</i>::EZ-Tn<i>5</i>. <b>B</b>. Disease severity of the <i>xopN</i>_<i>KXO85</i> mutants in the flag leaves of rice grown in a paddy field. W, water; 85, KXO85; N, KXO85 <i>xopN</i>_<i>KXO85</i>::EZ-Tn<i>5</i>; and N^C, KXO85 <i>xopN</i>_<i>KXO85</i>::EZ-Tn<i>5</i> (pML122G2). Photographs were taken and lesion lengths were determined 21 days after inoculation. Vertical error bars indicate the standard deviations (SD). The data are the averages of 12–15 replicates for each treatment. Columns and lines not connected by the same letter are significantly different (P<0.05) as determined by a one-way ANOVA (P<0.001) followed by post hoc Tukey HSD analysis. <b>C</b>. Bacterial growth patterns of the KXO85, <i>xopN</i>_<i>KXO85</i> mutant, and complemented <i>xopN</i>_<i>KXO85</i> mutant strains in flag leaves of wild-type Dongjin. The data are shown as the average values for three replicates; vertical bars indicate the error ranges (±SD). The bacterial populations were assessed every 3 days after inoculation. Different letters at day 21 indicate significant differences (P<0.05) as determined by a one-way ANOVA (P<0.001) followed by post hoc Tukey HSD analysis.</p

Interactions between XopN_KXO85 and OsVOZ2 and OsXNP.

<p><b>A</b>. Screening for interactors of XopN_KXO85 in rice using a yeast two-hybrid system. S (strong: pEXP ^TM32/Krev1 + pEXP ^TM22/RalGDS-wt), W (weak: pEXP ^TM32/Krev1 + pEXP ^TM22/RalGDS-m1), and A (absent: pEXP ^TM32/Krev1 + pEXP ^TM22/RalGDS-m2) indicate the strength of each interaction. Three independent and representative colonies are shown for each bait–prey combination. <b>B</b>. <i>In vivo</i> pull-down analysis of XopN_KXO85 and OsVOZ2 (left panel) and XopN_KXO85 and OsXNP (right panel). Total proteins from <i>N</i><i>. benthamiana</i> leaves co-expressing XopN_KXO85-6× His and Flag-OsVOZ2 or XopN_KXO85-6× His and OsXNP-Flag protein were purified by Ni⁺ affinity chromatography followed by Western blotting using anti-His and anti-Flag antibodies. The expected molecular weights were as follows: XopN_KXO85-6× His = 78.7 kDa; Flag-OsVOZ2 = 74.6 kDa; OsXNP-Flag = 40.1 kDa; +, protein expressed; and -, vector control. <b>C</b>. BiFC analysis of XopN_KXO85 -OsVOZ2, XopN_KXO85 -OsXNP, and XopN_KXO85 -OsVOZ1 interactions in <i>N</i><i>. benthamiana</i> leaves. Negative, pDEST-SCYNE(R)^GW + pDEST-SCYCE(R)^GW; positive, pEXP-SCYNE(R)-Cnx7 + pEXP-SCYCE(R)-Cnx6. Bars = 50 µm.</p

Data_Sheet_1_Nicotianamine Synthesis by OsNAS3 Is Important for Mitigating Iron Excess Stress in Rice.pdf

Iron (Fe) toxicity in plants causes tissue damage and cellular homeostasis disorders, thereby affecting plant growth and development. Nicotianamine (NA) is a ubiquitous chelator of metal cations and is responsible for metal homeostasis. Rice has three NA synthase (NAS) genes, of which the expression of OsNAS1 and OsNAS2 but not of OsNAS3 is strongly induced in response to Fe deficiency. Recently, we found that OsNAS3 expression is strongly induced with excess Fe in most rice tissues, particularly old leaves, suggesting that it may play a vital role under excess Fe conditions. However, the mechanism by which OsNAS3 responds to excess Fe in rice remains poorly understood. In this study, we clarified the physiological response of OsNAS3 expression to excess Fe and the role of NA synthesis in this condition. Promoter GUS analyses revealed that OsNAS3 was widely expressed in roots, especially in vascular bundle, epidermis, exodermis, stem, and old leaf tissues under Fe excess compared to control plants. Nicotianamine and deoxymugineic acid (DMA; a type of phytosiderophore synthesized by Strategy II species) were present in roots and shoots under Fe excess likewise under control conditions. In addition, OsNAS3 knockout plants were sensitive to excess Fe, exhibiting inferior growth, reduced dry weight, severer leaf bronzing, and greater Fe accumulation in their leaves than non-transformants with excess Fe. We also observed that NA-overproducing rice was tolerant of excess Fe. These results show that NA synthesized by OsNAS3 under Fe excess condition is to mitigate excess Fe whereas NA synthesized by OsNAS1 and OsNAS2 under normal Fe condition is to enhance Fe translocation, suggesting the different roles and functions of the NA existence between these two conditions. Overall, these findings suggest that rice synthesizes NA with OsNAS3 under Fe excess in roots and shoots, and that NA and DMA within the plant body are important for mitigating excess Fe stress and alleviating other metal deficiencies in rice. This report will be important for the development of tolerant rice adapted to Fe-contaminated soils.</p

Recombinant Expression and Characterization of the Cytoplasmic Rice β-Glucosidase Os1BGlu4

<div><p>The Os1BGlu4 β-glucosidase is the only glycoside hydrolase family 1 member in rice that is predicted to be localized in the cytoplasm. To characterize the biochemical function of rice Os1BGlu4, the <i>Os</i>1<i>bglu</i>4 cDNA was cloned and used to express a thioredoxin fusion protein in <i>Escherichia coli</i>. After removal of the tag, the purified recombinant Os1BGlu4 (rOs1BGlu4) exhibited an optimum pH of 6.5, which is consistent with Os1BGlu4's cytoplasmic localization. Fluorescence microscopy of maize protoplasts and tobacco leaf cells expressing green fluorescent protein-tagged Os1BGlu4 confirmed the cytoplasmic localization. Purified rOs1BGlu4 can hydrolyze <i>p</i>-nitrophenyl (<i>p</i>NP)-<i>β</i>-d-glucoside (<i>p</i>NPGlc) efficiently (<i>k</i>_cat/<i>K</i>_m  =  17.9 mM⁻¹·s⁻¹), and hydrolyzes <i>p</i>NP-<i>β</i>-d-fucopyranoside with about 50% the efficiency of the <i>p</i>NPGlc. Among natural substrates tested, rOs1BGlu4 efficiently hydrolyzed β-(1,3)-linked oligosaccharides of degree of polymerization (DP) 2–3, and β-(1,4)-linked oligosaccharide of DP 3–4, and hydrolysis of salicin, esculin and <i>p</i>-coumaryl alcohol was also detected. Analysis of the hydrolysis of <i>p</i>NP-<i>β</i>-cellobioside showed that the initial hydrolysis was between the two glucose molecules, and suggested rOs1BGlu4 transglucosylates this substrate. At 10 mM <i>p</i>NPGlc concentration, rOs1BGlu4 can transfer the glucosyl group of <i>p</i>NPGlc to ethanol and <i>p</i>NPGlc. This transglycosylation activity suggests the potential use of Os1BGlu4 for <i>p</i>NP-oligosaccharide and alkyl glycosides synthesis.</p></div

Virulence assay in wild-type Dongjin rice and the OsVOZ2 mutant line PFG_3A-07565.

<p><b>A</b>. Schematic representation of the T-DNA insertion in OsVOZ2 T₇ transgenic rice. <i>OsVOZ2</i> consists of four exons (orange boxes) and three introns (line between the orange boxes). The T-DNA was located in the second intron from the translational start site. F and R are the primers used for RT-PCR analysis, which showed the expected size of <i>OsVOZ2</i> in wild-type Dongjin but not in the <i>OsVOZ2</i> mutant rice PFG_3A-07565. Actin1 was used for normalization of the cDNA quantity. <b>B</b>. Virulence assay of the <i>xopN</i>_<i>KXO85</i> mutant in wild-type Dongjin rice and OsVOZ2 mutant rice. W, water; 85, KXO85; N, KXO85 <i>xopN</i>_<i>KXO85</i>::EZ-Tn<i>5</i>; and N^C, KXO85 <i>xopN</i>_<i>KXO85</i>::EZ-Tn<i>5</i> (pML122G2). Photographs were taken 21 days after inoculation. <b>C</b>. Measurement of disease severity in flag leaves of wild-type Dongjin rice (□) and OsVOZ2 mutant rice (▨). W, water; 85, KXO85; N, KXO85 <i>xopN</i>_<i>KXO85</i>::EZ-Tn<i>5</i>; and N^C, KXO85 <i>xopN</i>_<i>KXO85</i>::EZ-Tn<i>5</i> (pML122G2). Lesion lengths were determined 21 days after inoculation. Vertical error bars indicate the standard deviation (SD). The statistical significance was determined using a two-way ANOVA as compared to wild-type Dongjin rice with the post hoc Tukey HSD test (***, P<0.001). <b>D</b>. Growth patterns of the KXO85, <i>xopN</i>_<i>KXO85</i> mutant, and complemented <i>xopN</i>_<i>KXO85</i> mutant in the flag leaves of OsVOZ2 mutant rice (PFG_3A-07565). The data are the average values of three replicates; vertical bars indicate the error ranges (±SD). The bacterial populations were assessed every 3 days after inoculation. Different letters at day 21 indicate significant differences (P<0.05) as determined by a one-way ANOVA (P<0.001) followed by post hoc Tukey HSD analysis.</p

The subcellular localization of Os1BGlu4-GFP and GFP-Os1BGlu4.

<p>Subcellular localization of Os1BGlu4-GFP (A–C) and GFP- Os1BGlu4 (D-F) fusion proteins in maize protoplasts. Fluorescent GFP signals (A, D), chlorophyll autofluorescence (B, E) and merged images (C, F) are shown. C, chloroplast; V, vacuole. The bar in the merged images represents 5 µm.</p

The relative expression of <i>Os1bglu4</i> under wounding stress.

<p>The stressed <i>Os1bglu4</i> expression was determined by quantitative real-time RT-PCR relative to untreated rice with actin as a control gene at various numbers of minutes (min) after wounding of 10 day old rice seedling shoots. The data are given as mean + SE.</p

SDS-PAGE profiles of recombinant Os1BGlu4 expressed in Origami B(DE3).

<p>Lane 1, standard protein marker (Bio-RAD); Lane 2, crude Trx-His₆-rOs1BGlu4; lane 3, purified Trx-His₆-rOs1BGlu4; lane 4, Trx-His₆-rOs1BGlu4 cleaved by enterokinase; lane 5, purified rOs1BGlu4. The numbers 45 and 66 indicate the molecular weights in kDa of the most relevant protein standards. Each lane was loaded with 8 µl of the sample mixed with 2 µl 5× sample dye.</p