AtHSP17.8 overexpression in transgenic lettuce gives rise to dehydration and salt stress resistance phenotypes through modulation of ABA-mediated signaling

Key message

Transgenic Arabidopsis and lettuce plants overexpressing AtHSP17.8 showed ABA-hypersensitive but abiotic stress-resistant phenotypes. ABA treatment caused a dramatic induction of early ABA-responsive genes in AtHSP17.8 -overexpressing transgenic lettuce.

Abstract

Plant small heat shock proteins function as chaperones in protein folding. In addition, they are involved in responses to various abiotic stresses, such as dehydration, heat and high salinity in Arabidopsis. However, it remains elusive how they play a role in the abiotic stress responses at the molecular level. In this study, we provide evidence that Arabidopsis HSP17.8 (AtHSP17.8) positively regulates the abiotic stress responses by modulating abscisic acid (ABA) signaling in Arabidopsis, and also in lettuce, a heterologous plant when ectopically expressed. Overexpression of AtHSP17.8 in both Arabidopsis and lettuce leads to hypersensitivity to ABA and enhanced resistance to dehydration and high salinity stresses. Moreover, early ABA-responsive genes, ABI1, ABI5, NCED3, SNF4 and AREB2, were rapidly induced in AtHSP17.8-overexpressing transgenic Arabidopsis and lettuce. Based on these data, we propose that AtHSP17.8 plays a crucial role in abiotic stress responses by positively modulating ABA-mediated signaling in both Arabidopsis and lettuce. Moreover, our results suggest that stress-tolerant lettuce can be engineered using the genetic and molecular resources of Arabidopsis.     

The <Emphasis Type="Italic">Populus trichocarpa PtHSP17.8</Emphasis> involved in heat and salt stress tolerances

Key message

PtHSP17.8 was regulated by various abiotic stresses. Overexpression of PtHSP17.8 enhanced the tolerance to heat and salt stresses through maintain ROS homeostasis and cooperate with stress-related genes in Arabidopsis.

Abstract

Small heat shock proteins (sHSPs) play important roles in response to diverse biotic and abiotic stresses, especially in heat tolerance. However, limited information is available on the stress tolerance roles of sHSPs in woody species. To explore the function of sHSPs in poplar, we isolated and characterized PtHSP17.8 from Populus trichocarpa. Phylogenetic analysis and subcellular localization revealed that PtHSP17.8 was a cytosolic class I sHSP. The gene expression profile of PtHSP17.8 in various tissues showed that it was significantly accumulated in stem and root, which was consistent with the GUS expression pattern driven by promoter of PtHSP17.8. The expression of PtHSP17.8 could be induced by various abiotic stresses and significantly activated by heat stress. Overexpression of PtHSP17.8 enhanced the tolerance to heat and salt stresses in Arabidopsis. The seedling survival rate, root length, relative water content, antioxidative enzyme activities, proline, and soluble sugar content were increased in transgenic Arabidopsis under heat and salt stresses, but not in normal condition. The co-expression network of PtHSP17.8 were constructed and demonstrated many stress responsive genes included. The stress-related genes in the co-expression network were up-regulated in the PtHSP17.8 overexpression seedlings. These results suggest that PtHSP17.8 confers heat and salt tolerances in plants.

     

<Emphasis Type="Italic">MsZEP</Emphasis>, a novel zeaxanthin epoxidase gene from alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis>), confers drought and salt tolerance in transgenic tobacco

Key message

The zeaxanthin epoxidase gene ( MsZEP ) was cloned and characterized from alfalfa and validated for its function of tolerance toward drought and salt stresses by heterologous expression in Nicotiana tabacum.

Abstract

Zeaxanthin epoxidase (ZEP) plays important roles in plant response to various environment stresses due to its functions in ABA biosynthetic and the xanthophyll cycle. To understand the expression characteristics and the biological functions of ZEP in alfalfa (Medicago sativa), a novel gene, designated as MsZEP (KM044311), was cloned, characterized and overexpressed in Nicotiana tabacum. The open reading frame of MsZEP contains 1992 bp nucleotides and encodes a 663-amino acid polypeptide. Amino acid sequence alignment indicated that deduced MsZEP protein was highly homologous to other plant ZEP sequences. Phylogenetic analysis showed that MsZEP was grouped into a branch with other legume plants. Real-time quantitative PCR revealed that MsZEP gene expression was clearly tissue-specific, and the expression levels were higher in green tissues (leaves and stems) than in roots. MsZEP expression decreased in shoots under drought, cold, heat and ABA treatment, while the expression levels in roots showed different trends. Besides, the results showed that nodules could up-regulate the MsZEP expression under non-stressful conditions and in the earlier stage of different abiotic stress. Heterologous expression of the MsZEP gene in N. tabacum could confer tolerance to drought and salt stress by affecting various physiological pathways, ABA levels and stress-responsive genes expression. Taken together, these results suggested that the MsZEP gene may be involved in alfalfa responses to different abiotic stresses and nodules, and could enhance drought and salt tolerance of transgenic tobacco by heterologous expression.

     

An aquaporin gene from halophyte <Emphasis Type="Italic">Sesuvium portulacastrum</Emphasis>, <Emphasis Type="Italic">SpAQP1</Emphasis>, increases salt tolerance in transgenic tobacco

Key message

SpAQP1 was strongly induced by salt in an ABA-independent way, promoted seed germination and root growth in transgenic tobaccos and increased salt tolerance by increasing the activities of antioxidative enzymes.

Abstract

Aquaporin (AQP) plays crucial roles in the responses of plant to abiotic stresses such as drought, salt and cold. Compared to glycophytes, halophytes often have excellent salt and drought tolerances. To uncover the molecular mechanism of halophyte Sesuvium portulacastrum tolerance to salt, in this study, an AQP gene, SpAQP1, from S. portulacastrum was isolated and characterized. The amino acid sequence of SpAQP1 shared high homology with that of plant plasma membrane intrinsic proteins (PIPs) and contained the distinct molecular features of PIPs. In the phylogenic tree, SpAQP1 was evidently classified as the PIP2 subfamily. SpAQP1 is expressed in roots, stems and leaves, and was significantly induced by NaCl treatment and inhibited by abscisic acid (ABA) treatment. When heterologously expressed in yeast and tobacco, SpAQP1 enhanced the salt tolerance of yeast strains and tobacco plants and promoted seed germination and root growth under salt stress in transgenic plants. The activity of antioxidative enzymes including superoxide dismutase, peroxidase and catalase was increased in transgenic plants overexpressing SpAQP1. Taken together, our studies suggested that SpAQP1 functioned in the responses of S. portulacastrum to salt stress and could increase salt tolerance by enhancing the antioxidative activity of plants.

     

New phenotypic characteristics of three tmm alleles in Arabidopsis thaliana

Key message

Three new tmm mutants were isolated and showed differential phenotypes from tmm - 1 , and TMM overexpression led to abnormal leaf trichomes.

Abstract

TOO MANY MOUTH (TMM) plays a significant role in the stomatal signal transduction pathway, which involves in the regulation of stomatal distribution and patterning. Three mutants with clustered stomata were isolated and identified as new alleles of tmm. tmm-4 mutation included a base transversion from adenine to thymidine in position 1,033 of the TMM coding region and resulted in premature termination of translation at position 345 of TMM. tmm-5 had a base transition from cytosine to thymidine in 244 of TMM and translated 82 amino acids before premature termination. tmm-6 mutation took a base transition from guanine to adenine in 463 of TMM and changed a glycine (Gly) to an arginine (Arg) in position 155 of the protein. tmm-6 had an evident reduction of stomatal clusters and fewer stomata in cluster compared with other tmm alleles, possibly due to decreased level of entry divisions in cells next to two stomata or their precursors. tmm-5 and tmm-6 were hypersensitive to abscisic acid (ABA) in seedling growth and seed germination, while tmm-4 was defective in response to ABA during seed dormancy, suggesting that TMM was involved in ABA signaling transduction. Interestingly, overexpression of TMM resulted in the reduction of leaf trichomes and their branches, and this might reveal a new function of TMM in trichome development.     

Cloning,characterization and functional analysis of the role MhNCED3, a gene encoding 9-cis-epoxycarotenoid dioxygenase in Malus hupehensis Rehd., plays in plant tolerance to osmotic and Cd2+ stresses

Aims

Abscisic acid (ABA) plays an important role in the stress tolerance of seedlings and 9-cis-epoxycarotenoid dioxygenase (NCED) is considered to be the rate-limiting enzyme involved in ABA biosynthesis. However, the genes encoding NCED in M. hupehensis Rehd. have not been reported.

Methods

In this study, a gene encoding NCED, MhNCED3, was isolated from the roots of M. hupehensis Rehd. Its functions were investigated in M. hupehensis Rehd. seedlings and transgenic Arabidopsis lines under various abiotic stresses.

Results

The expression of MhNCED3 in M. hupehensis Rehd. roots was differentially induced by dehydration, chilling, salt and cadmium stresses and ABA biosynthesis was highly correlated with MhNCED3 expression. Ectopic expression of MhNCED3 successfully complemented the phenotypic defects of the 129B08/nced3 mutant. Furthermore, overexpression of MhNCED3, when it was transformed into the wild type (WT) seedling resulted in enhanced tolerance to osmotic and cadmium stresses compared to the normal WT seedling. The transgenic lines displayed higher rates of seed germination, improved growth and developmental status, reduced water loss/oxidative damage, lowered apoptosis rates and increased ABA accumulation. Furthermore, the higher antioxidant enzyme activities detected in the transgenic lines were probably responsible for the decrease in oxidative damage and apoptosis rates.

Conclusions

Overall, MhNCED3 played a significant role in enhancing plant tolerance to abiotic stresses through the regulation of endogenous ABA biosynthesis.     

QTL mapping for salt tolerance and domestication-related traits in Vigna marina subsp. oblonga,a halophytic species

Key message

QTL mapping in F ₂ population [ V. luteola × V. marina subsp. oblonga ] revealed that the salt tolerance in V. marina subsp. oblonga is controlled by a single major QTL.

Abstract

The habitats of beach cowpea (Vigna marina) are sandy beaches in tropical and subtropical regions. As a species that grows closest to the sea, it has potential to be a gene source for breeding salt-tolerant crops. We reported here for the first time, quantitative trait loci (QTLs) mapping for salt tolerance in V. marina. A genetic linkage map was constructed from an F₂ population of 120 plants derived from an interspecific cross between V. luteola and V. marina subsp. oblonga. The map comprised 150 SSR markers. The markers were clustered into 11 linkage groups spanning 777.6 cM in length with a mean distance between the adjacent markers of 5.59 cM. The F_2:3 population was evaluated for salt tolerance under hydroponic conditions at the seedling and developmental stages. Segregation analysis indicated that salt tolerance in V. marina is controlled by a few genes. Multiple interval mapping consistently identified one major QTL which can explain about 50 % of phenotypic variance. The flanking markers may facilitate transfer of the salt tolerance allele from V. marina subsp. oblonga into related Vigna crops. The QTL for domestication-related traits from V. marina are also discussed.