Expression profiles and hormonal regulation of tobacco expansin genes and their involvement in abiotic stress response.
Changes in the expression levels of tobacco expansin genes NtEXPA1, NtEXPA4, NtEXPA5, and NtEXPA6 were studied in different organs of tobacco (Nicotiana tabacum L.) as well as in response to phytohormone and stress treatments. It was shown that NtEXPA1, NtEXPA4 and NtEXPA5 transcripts were predominantly expressed in the shoot apices and young leaves, but almost absent in mature leaves and roots. The NtEXPA6 mRNA was found at high levels in calluses containing a large number of undifferentiated cells, but hardly detectable in the leaves of different ages and roots. In young leaves, expression levels of NtEXPA1, NtEXPA4 and NtEXPA5 genes were induced by cytokinins, auxins and gibberellins. Cytokinins and auxins were also found to increase NtEXPA6 transcripts in young leaves but to the much lower levels than the other expansin mRNAs. Expression analysis demonstrated that brassinosteroid phytohormones were able either to up-regulate or to down-regulate expression of different expansins in leaves of different ages. Furthermore, transcript levels of NtEXPA1, NtEXPA4, and NtEXPA5 genes were increased in response to NaCl, drought, cold, heat, and 10μM abscisic acid (ABA) treatments but reduced in response to more severe stresses, i.e. cadmium, freezing, and 100μM ABA. In contrast, no substantial changes were found in NtEXPA6 transcript level after all stress treatments. In addition, we examined the involvement of tobacco expansins in the regulation of abiotic stress tolerance by transgenic approaches. Transgenic tobacco plants with constitutive expression of NtEXPA1 and NtEXPA5 exhibited improved tolerance to salt stress: these plants showed higher growth indices after NaCl treatment and minimized water loss by reducing stomatal density. In contrast, NtEXPA4-silenced plants were characterized by a considerable growth reduction under salinity and enhanced water loss. Our findings indicate that expression levels of all studied tobacco expansins genes are modulated by plant hormones whereas NtEXPA1, NtEXPA4, and NtEXPA5 expansins may be involved in the regulation of stress tolerance in tobacco plants.
Institute of Biochemistry and Genetics, Ufa Research Centre, Russian Academy of Sciences, pr. Oktyabrya 71, Ufa 450054, Russia. Electronic address: kuluev@bk.ru.
Bulat
B
Kuluev
Institute of Biochemistry and Genetics, Ufa Research Centre, Russian Academy of Sciences, pr. Oktyabrya 71, Ufa 450054, Russia. Electronic address: avalbaev@yahoo.com.
Azamat
A
Avalbaev
Institute of Biochemistry and Genetics, Ufa Research Centre, Russian Academy of Sciences, pr. Oktyabrya 71, Ufa 450054, Russia.
Elena
E
Mikhaylova
Institute of Biochemistry and Genetics, Ufa Research Centre, Russian Academy of Sciences, pr. Oktyabrya 71, Ufa 450054, Russia.
Yuriy
Y
Nikonorov
Institute of Biochemistry and Genetics, Ufa Research Centre, Russian Academy of Sciences, pr. Oktyabrya 71, Ufa 450054, Russia.
Zoya
Z
Berezhneva
Institute of Biochemistry and Genetics, Ufa Research Centre, Russian Academy of Sciences, pr. Oktyabrya 71, Ufa 450054, Russia.
Alexey
A
Chemeris
D000040:Abscisic Acid / Q000494:pharmacology; D000085:Acetates / Q000494:pharmacology; D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics; D003517:Cyclopentanes / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D017343:Genes, Plant; D009928:Organ Specificity / Q000187:drug effects / Q000235:genetics; D054883:Oxylipins / Q000494:pharmacology; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics; D054046:Plant Stomata / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D018526:Plant Transpiration / Q000187:drug effects / Q000235:genetics; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics*; D014026:Nicotiana / Q000235:genetics* / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
D000085:Acetates; D003517:Cyclopentanes; D054883:Oxylipins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D012333:RNA, Messenger; C095825:expansin protein, plant; D000040:Abscisic Acid; C072239:methyl jasmonate
Abiotic stress responses; Expansins; Nicotiana tabacum L.; Phytohormones