Search

Desiccation tolerance is an ancestral feature of land plants and is still retained in non-vascular plants such as bryophytes and some vascular plants. However, except for seeds and spores, this trait is absent in vegetative tissues of vascular plants. Although many studies have focused on understanding the molecular basis underlying desiccation tolerance using transcriptome and proteome approaches, the critical molecular differences between desiccation tolerant plants and non-desiccation plants are still not clear. The moss Physcomitrella patens cannot survive rapid desiccation under laboratory conditions, but if cells of the protonemata are treated by the phytohormone abscisic acid (ABA) prior to desiccation, it can survive 24 h exposure to desiccation and regrow after rehydration. The desiccation tolerance induced by ABA (AiDT) is specific to this hormone, but also depends on a plant transcription factor ABSCISIC ACID INSENSITIVE3 (ABI3). Here we report the comparative proteomic analysis of AiDT between wild type and ABI3 deleted mutant (Δabi3) of P. patens using iTRAQ (Isobaric Tags for Relative and Absolute Quantification). From a total of 1980 unique proteins that we identified, only 16 proteins are significantly altered in Δabi3 compared to wild type after desiccation following ABA treatment. Among this group, three of the four proteins that were severely affected in Δabi3 tissue were Arabidopsis orthologous genes, which were expressed in maturing seeds under the regulation of ABI3. These included a Group 1 late embryogenesis abundant (LEA) protein, a short-chain dehydrogenase, and a desiccation-related protein. Our results suggest that at least three of these proteins expressed in desiccation tolerant cells of both Arabidopsis and the moss are very likely to play important roles in acquisition of desiccation tolerance in land plants. Furthermore, our results suggest that the regulatory machinery of ABA- and ABI3-mediated gene expression for desiccation tolerance might have evolved in ancestral land plants before the separation of bryophytes and vascular plants., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Eutrema salsugineum (also known as Thellungiella salsuginea and formerly Thellungiella halophila), a species closely related to Arabidopsis thaliana, shows tolerance not only to salt stress, but also to chilling, freezing, and high temperatures. To identify genes responsible for stress tolerance, we conducted Full-length cDNA Over-eXpressing gene (FOX) hunting among a collection of E. salsugineum cDNAs that were stress-induced according to gene ontology analysis or over-expressed in E. salsugineum compared with A. thaliana. We identified E. salsugineum CSP41b (chloroplast stem-loop-binding protein of 41 kDa; also known as CRB, chloroplast RNA binding; named here as EsCSP41b) as a gene that can confer heat and salinity stress tolerance on A. thaliana. A. thaliana CSP41b is reported to play an important role in the proper functioning of the chloroplast: the atcsp41b mutant is smaller and paler than wild-type plants and shows altered chloroplast morphology and photosynthetic performance. We observed that AtCSP41b-overexpressing transgenic A. thaliana lines also exhibited marked heat tolerance and significant salinity stress tolerance. The EsCSP41b-overexpressing transgenic A. thaliana lines showed significantly higher photosynthesis activity than wild-type plants not only under normal growth conditions but also under heat stress. In wild-type plants, the expression levels of both EsCSP41b and AtCSP41b were significantly reduced under heat or salinity stress. We conclude that maintenance of CSP41b expression under abiotic stresses may alleviate photoinhibition and improve survival under such stresses., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The phytohormone ABA and the transcription factor ABSCISIC ACID INSENSITIVE 3 (ABI3)/VIVIPAROUS 1 (VP1) function in protecting embryos during the desiccation stage of seed development. In a similar signaling pathway, vegetative tissue of the moss Physcomitrella patens survives desiccation by activating downstream genes (e.g. LEA1) in response to ABA and ABI3. We show that the PpLEA1 promoter responds to PpABI3 primarily through the ACTT-core element (5'-TCCACTTGTC-3'), while the ACGT-core ABA-responsive element (ABRE) appears to respond to ABA alone. We also found by yeast-two-hybrid screening that PpABI3A interacts with PpNF-YC1, a subunit of CCAAT box binding factor (CBF)/nuclear factor Y (NF-Y). PpNF-YC1 increased the activation of the PpLEA1 promoter when incubated with PpABI3A, as did NF-YB, NF-YC, and ABI3 from Arabidopsis. This new response element (ACTT) is responsible for activating the ABI3-dependent ABA response pathway cooperatively with the nuclear factor Y (NF-Y) complex. These results further define the regulatory interactions at the transcriptional level for the expression of this network of genes required for drought/desiccation tolerance. This gene regulatory set is in large part conserved between vegetative tissue of bryophytes and seeds of angiosperms and will shed light on the evolution of this pathway in the green plant lineage., (© 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.)

Thellungiella salsuginea (formerly T. halophila), a species closely related to Arabidopsis (Arabidopsis thaliana), is tolerant not only to high salt levels, but also to chilling, freezing, and ozone. Here, we report that T. salsuginea also shows greater heat tolerance than Arabidopsis. We identified T. salsuginea HsfA1d (TsHsfA1d) as a gene that can confer marked heat tolerance on Arabidopsis. TsHsfA1d was identified via Full-length cDNA Over-eXpressing gene (FOX) hunting from among a collection of heat-stress-related T. salsuginea cDNAs. Transgenic Arabidopsis overexpressing TsHsfA1d showed constitutive up-regulation of many genes in the Arabidopsis AtHsfA1 regulon under normal growth temperature. In Arabidopsis mesophyll protoplasts, TsHsfA1d was localized in both the nucleus and the cytoplasm. TsHsfA1d also interacted with AtHSP90, which negatively regulates AtHsfA1s by forming HsfA1-HSP90 complexes in the cytoplasm. It is likely that the partial nuclear localization of TsHsfA1d induced the expression of the AtHsfA1d regulon in the transgenic plants at normal temperature. We also discovered that transgenic Arabidopsis plants overexpressing AtHsfA1d were more heat-tolerant than wild-type plants and up-regulated the expression of the HsfA1d regulon, as was observed in TsHsfA1d-overexpressing plants. We propose that the products of both TsHsfA1d and AtHsfA1d function as positive regulators of Arabidopsis heat-stress response and would be useful for the improvement of heat-stress tolerance in other plants.

The transcription factors dehydration-responsive element-binding protein 1s (DREB1s)/C-repeat-binding factors (CBFs) specifically interact with the DRE/CRT cis-acting element and control the expression of many stress-inducible genes in Arabidopsis. The genes for DREB1 orthologs, OsDREB1A and OsDREB1B from rice, are induced by cold stress, and overexpression of DREB1 or OsDREB1 induced strong expression of stress-responsive genes in transgenic Arabidopsis plants, resulting in increased tolerance to high-salt and freezing stresses. In this study, we generated transgenic rice plants overexpressing the OsDREB1 or DREB1 genes. These transgenic rice plants showed not only growth retardation under normal growth conditions but also improved tolerance to drought, high-salt and low-temperature stresses like the transgenic Arabidopsis plants overexpressing OsDREB1 or DREB1. We also detected elevated contents of osmoprotectants such as free proline and various soluble sugars in the transgenic rice as in the transgenic Arabidopsis plants. We identified target stress-inducible genes of OsDREB1A in the transgenic rice using microarray and RNA gel blot analyses. These genes encode proteins that are thought to function in stress tolerance in the plants. These results indicate that the DREB1/CBF cold-responsive pathway is conserved in rice and the DREB1-type genes are quite useful for improvement of stress tolerance to environmental stresses in various kinds of transgenic plants including rice.