Izabella Kovács

Proline accumulation and AtP5CS2 gene activation are induced by plant-pathogen incompatible interactions in Arabidopsis.

Accumulation of free L-proline (Pro) is a typical stress response incited by osmotic injuries in plants and microorganisms. Although the protective role of Pro in osmotic stress is not well understood, it is thought to function as compatible osmolyte or as a scavenger of reactive oxygen species (ROS). Here we show that, in Arabidopsis thaliana, Pro biosynthesis can be activated by incompatible plant-pathogen interactions triggering a hypersensitive response (HR). Pro accumulates in leaf tissues treated with Pseudomonas syringae pv. tomato avirulent strains (avrRpt2 and avrRpm1) but remains unchanged in leaves infected with isogenic virulent bacteria. Incompatible interactions lead to transcriptional activation of AtP5CS2, but not AtP5CS1, encoding the rate limiting enzyme in Pro biosynthesis pyrroline-5-carboxylate synthase (P5CS). AtP5CS2:GUS and AtP5CS2:LUC transgenes were induced inside and around the HR lesions produced by avirulent Pseudomonas spp. in transgenic plants. Pro accumulation was faster and stronger when stimulated by avrRpm1 than by avrRpt2, and was compromised in the low-salicylic acid plants NahG and eds5 when signaled through the RPS2-dependent pathway. In addition, Pro content and AtP5CS2 expression were enhanced by ROS in wild-type plants, suggesting that ROS may function as an intermediate signal in AtP5CS2-mediated Pro accumulation.

Nuclear localization of a hypoxia-inducible novel non-symbiotic hemoglobin in cultured alfalfa cells1

We have isolated a 483‐bp‐long full‐length cDNA clone encoding a non‐symbiotic hemoglobin called Mhb1, the first one found in alfalfa. This non‐symbiotic hemoglobin is a single copy gene localized in linkage group 4 in diploid Medicago genome. The Mhb1 mRNA was found only in the roots of alfalfa plants. The Mhb1 gene was inducible by hypoxia and showed no induction by cold stress treatment. The Mhb1 transcript level increased at the G2/M boundary in a synchronized alfalfa cell suspension culture. The majority of Mhb1 protein was shown to be localized in the nucleus and smaller amounts were detected in the cytoplasm. A potential link to the nitric oxide signalling pathway is also discussed.

Gene Trapping with Firefly Luciferase in Arabidopsis. Tagging of Stress-Responsive Genes

To monitor the expression of T-DNA-tagged plant genes in vivo, a collection of 20,261 transgenic lines of Arabidopsis (Columbia-0) were generated with the promoter trap vector pTluc, which carries a promoterless firefly luc (luciferase) reporter gene linked to the right T-DNA border. By detection of bioluminescence in 3-week-old seedlings, 753 lines were identified showing constitutive, organ-specific, and stress-responsive luciferase expression patterns. To facilitate the identification of well-defined luciferase expression patterns, a pooled seed stock was established. Several lines showed sugar, salt, and abscisic acid (ABA)-inducible luciferase activity. Segregation analysis of 215 promoter trap lines indicated that about 50% of plants contained single insertions, whereas 40% carried two and 10% carried three or more T-DNA tags. Sequencing the T-DNA insert junctions isolated from 17 luciferase-expressing lines identified T-DNA tags in 5′- and 3′-transcribed domains and translational gene fusions generated by T-DNA insertions in exons and introns of Arabidopsis genes. Tissue specific expression of eight wild-type Arabidopsis genes was confirmed to be similar to the luminescence patterns observed in the corresponding luciferase-tagged lines. Here, we describe the characterization of a transcriptional luc reporter gene fusion with the WBC-type ABC transporter gene At1g17840. Expression of wild-type and luciferase-tagged At1g17840 alleles revealed similar induction by salt, glucose, and ABA treatments and gibberellin-mediated down-regulation of ABA-induced expression. These results illustrate that luciferase gene traps are well suited for monitoring the expression of stress-responsive Arabidopsis genes in vivo.

Corrigendum to: Nuclear localization of a hypoxia-inducible novel non-symbiotic hemoglobin in cultured alfalfa cells1: [FEBS Letters 482 (2000) 125–130]

Corrigendum to: Nuclear localization of a hypoxia-inducible novel non-symbiotic hemoglobin in cultured alfalfa cells1 [FEBS Letters 482 (2000) 125^130]C Csaba Seregelyesa, Laszlo Mustardya, Ferhan Ayaydina, Laszlo Sassa, Laszlo Kovacsa, Gabriella Endreb, Noemi Lukacsa, Izabella Kovacsa, Imre Vassa, Gyo«rgy B. Kissb, Gabor V. Horvatha;c, Denes Duditsa;c;* aInstitute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, 6701 Szeged, Hungary bInstitute of Genetics, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, 6701 Szeged, Hungary cBiotechnology Institute, Bay Zoltan Applied Research Foundation, Derkovits fasor 2, 6726 Szeged, Hungary

Erratum: Nuclear localization of a hypoxia-inducible novel non-symbiotic hemoglobin in cultured alfalfa cells (Febs Letters (2000) 482 (125-130) PII: S0014579300020494)

Corrigendum to: Nuclear localization of a hypoxia-inducible novel non-symbiotic hemoglobin in cultured alfalfa cells1 [FEBS Letters 482 (2000) 125^130]C Csaba Seregelyesa, Laszlo Mustardya, Ferhan Ayaydina, Laszlo Sassa, Laszlo Kovacsa, Gabriella Endreb, Noemi Lukacsa, Izabella Kovacsa, Imre Vassa, Gyo«rgy B. Kissb, Gabor V. Horvatha;c, Denes Duditsa;c;* aInstitute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, 6701 Szeged, Hungary bInstitute of Genetics, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, 6701 Szeged, Hungary cBiotechnology Institute, Bay Zoltan Applied Research Foundation, Derkovits fasor 2, 6726 Szeged, Hungary