Pattern of CsICE1 expression under cold or drought treatment and functional verification through analysis of transgenic Arabidopsis

Development of Agrobacterium-mediated in planta transformation protocol through coleoptile in rice

Genetic modification of rice is mainly carried out by Agrobacterium-mediated transformation of callus accompanied by tissue culture. It is time consuming, laborious and unapplicable for cultivars unable to induce callus. In this study, we have reported a novel gene transfer protocol that involves pulling out primary leaf from coleoptile and injection of Agrobacterium culture into the empty channel. Out of 25 plants survived after injection of Agrobacterium tumefaciens EHA105 culture harboring pCAMBIA1301-RD29A-AtDREB1A, 8 T0 plants revealed the expected size of around 811 bp corresponding to AtDREB1A gene and Southern blotting analysis on 18 T1 plants suggested introgression of AtDREB1A. 3 T2 lines (7-9, 12-3, 18-6) exhibited accumulation of free proline and soluble sugars, yet increase of chlorophyll content, but decrease of electrolyte leakage and methane dicarboxylic aldehyde under cold stress condition at the vegetative growth stage. Yield components investigation on T2 lines showed earlier heading date and no yield loss compared to wild type plants grown under normal condition. GUS expression analysis and integrated transgene detection in T0 and T1 plants followed by evaluation of cold stress tolerance in T2 lines suggest the advantage of this in planta transformation protocol to obtain transgenic rice.

Enhancement of plant cold tolerance by soybean RCC1 family gene GmTCF1a

BACKGROUND

Low temperature severely limits the growth, yield, and geographic distributions of soybean. Soybean plants respond to cold stress by reprogramming the expression of a series of cold-responsive genes. However, the intrinsic mechanism underlying cold-stress tolerance in soybean remains unclear. A. thaliana tolerant to chilling and freezing 1 (AtTCF1) is a regulator of chromosome condensation 1 (RCC1) family protein and regulates freezing tolerance through an independent C-repeat binding transcription factor (CBF) signaling pathway.

RESULTS

In this study, we identified a homologous gene of AtTCF1 in soybean (named GmTCF1a), which mediates plant tolerance to low temperature. Like AtTCF1, GmTCF1a contains five RCC1 domains and is located in the nucleus. GmTCF1a is strongly and specifically induced by cold stress. Interestingly, ectopic overexpression of GmTCF1a in Arabidopsis greatly increased plant survival rate and decreased electrolyte leakage under freezing stress. A cold-responsive gene, COR15a, was highly induced in the GmTCF1a-overexpressing transgenic lines.

CONCLUSIONS

GmTCF1a responded specifically to cold stress, and ectopic expression of GmTCF1a enhanced cold tolerance and upregulated COR15a levels. These results indicate that GmTCF1a positively regulates cold tolerance in soybean and may provide novel insights into genetic improvement of cold tolerance in crops.

Overexpression of Arabidopsis ICE1 enhances yield and multiple abiotic stress tolerance in indica rice

ICE1 (Inducer of CBF Expression 1), a MYC-type bHLH transcription factor, is a regulator of cold tolerance in Arabidopsis. Indica rice, which occupies the major rice cultivated area, is highly sensitive to cold stress. Hence in this study, Arabidopsis ICE1 (AtICE1) was overexpressed in indica rice to analyze its role in reproductive stage cold and other abiotic stress tolerance to indica rice. AtICE1 was overexpressed by using stress inducible AtRD29A promoter in mega rice cv. MTU1010. Under cold stress conditions, AtICE1 overexpression lines showed lower accumulation of MDA and H2O2, higher membrane stability, and thus higher seedling survival rate than the WT plants. Expression levels of OsDREB1A, OsMYB3R2, and OsTPP1 were significantly higher in transgenics as compared with WT under cold stress conditions. AtICE1 transgenic rice plants produced 44-60% higher grain yield as compared with WT plants under control conditions in three independent experiments. Of the three AtICE1 overexpression lines, two lines produced significantly higher grain yield as compared with WT plants after recovery from cold, salt and drought stresses. AtICE1 overexpression lines showed significantly higher stomatal density and conductance under non-stress conditions. qRT-PCR analysis showed that expression levels of stomatal pathway genes viz., OsSPCH1, OsSPCH2, OsSCR1, OsSCRM1, OsSCRM2 and OsMUTE were significantly higher in AtICE1 transgenics as compared with WT plants. The components of water use viz., stomatal conductance, photosynthesis, and instantaneous WUE were higher in transgenics as compared with WT plants. The results showed that AtICE1 confers multiple stress tolerance to indica rice, and the role of ICE1 in stress tolerance and stomatal development is conserved across species.

Genes underlying cold acclimation in the tea plant (<i>Camellia sinensis</i> (L.) Kuntze)

The article reviews the latest studies showing the diversity of genetic mechanisms and gene families underlying the increased cold and frost tolerance of tea and other plant species. It has been shown that cell responses to chilling (0…+15°C) and freezing (< 0°C) are not the same and gene expression under cold stress is genotype-specific. In recent decades, progress has been made in understanding the genetic mechanisms underlying the cold response of plants – ICE1 (inducer of CBF expression 1), CBF (C-repeat-binding factor), COR (cold-regulated genes) pathways and signaling have been discovered. The ICE, CBF and DHN gene groups play a key role in the cold acclimation of the tea plant. The accumulation of CBF transcripts occurs after 15 min of chilling induction, and longer cold stress leads to accumulation of CBF transcripts. It is shown that the transcripts of the CsDHN1, CsDHN2 and CsDHN3 genes accumulate at a higher level in resistant genotypes of tea in comparison with susceptible cultivars during freezing. CBF-independent pathways include genes involved in metabolism and transcription factors such as HSFC1, ZAT12, CZF1, PLD (phospholipase D), WRKY, HD-Zip, CsLEA, LOX, NAC, HSP, which are widely distributed in plants and are involved in the basic mechanisms of tea resistance to cold and frost. The most recent studies show an important role of miRNA in the mechanisms of response to chilling and freezing in tea. The data obtained on different plant species may correlate with the mechanisms of frost tolerance of tea and are the basis for future studies of the signaling pathways of response to cold in the tea plant. The results of the research emphasize the need to further explore the ways in which various genes regulate the tolerance of tea to cold stress to find the molecular markers of frost tolerance.

Low-temperature tolerance in land plants: Are transcript and membrane responses conserved?

Plants' tolerance of low temperatures is an economically and ecologically important limitation on geographic distributions and growing seasons. Tolerance for low temperatures varies significantly across different plant species, and different mechanisms likely act in different species. In order to survive low-temperature stress, plant membranes must maintain their fluidity in increasingly cold and oxidative cellular environments. The responses of different species to low-temperature stress include changes to the types and desaturation levels of membrane lipids, though the precise lipids affected tend to vary by species. Regulation of membrane dynamics and other low-temperature tolerance factors are controlled by both transcriptional and post-transcriptional mechanisms. Here, we review low-temperature induced changes in both membrane lipid composition and gene transcription across multiple related plant species with differing degrees of low-temperature tolerance. We attempt to define a core set of changes for transcripts and lipids across species and treatment variations. Some responses appear to be consistent across all species for which data are available, while many others appear likely to be species or family-specific. Potential rationales are presented, including variance in testing, reporting and the importance of considering the level of stress perceived by the plant.

Tea plant SWEET transporters: expression profiling, sugar transport, and the involvement of CsSWEET16 in modifying cold tolerance in Arabidopsis

Thirteen SWEET transporters were identified in Camellia sinensis and the cold-suppression gene CsSWEET16 contributed to sugar compartmentation across the vacuole and function in modifying cold tolerance in Arabidopsis. The sugars will eventually be exported transporters (SWEET) family of sugar transporters in plants is a recently identified protein family of sugar uniporters that contain seven transmembrane helices harbouring two MtN3 motifs. SWEETs play important roles in various biological processes, including plant responses to environmental stimuli. In this study, 13 SWEET transporters were identified in Camellia sinensis and were divided into four clades. Transcript abundances of CsSWEET genes were detected in various tissues. CsSWEET1a/1b/2a/2b/2c/3/9b/16/17 were expressed in all of the selected tissues, whereas the expression of CsSWEET5/7/9a/15 was not detected in some tissues, including those of mature leaves. Expression analysis of nine CsSWEET genes in leaves in response to abiotic stresses, natural cold acclimation and Colletotrichum camelliae infection revealed that eight CsSWEET genes responded to abiotic stress, while CsSWEET3 responded to C. camelliae infection. Functional analysis of 13 CsSWEET activities in yeast revealed that CsSWEET1a/1b/7/17 exhibit transport activity for glucose analogues and other types of hexose molecules. Further characterization of the cold-suppression gene CsSWEET16 revealed that this gene is localized in the vacuolar membrane. CsSWEET16 contributed to sugar compartmentation across the vacuole and function in modifying cold tolerance in Arabidopsis. Together, these findings demonstrate that CsSWEET genes play important roles in the response to abiotic and biotic stresses in tea plants and provide insights into the characteristics of SWEET genes in tea plants, which could serve as the basis for further functional identification of such genes.

Genome-wide transcriptome profiling provides overwintering mechanism of Agropyron mongolicum

BACKGROUND

The mechanism of winter survival for perennials involves multiple levels of gene regulation, especially cold resistance. Agropyron mongolicum is one important perennial grass species, but there is little information regarding its overwintering mechanism. We performed a comprehensive transcriptomics study to evaluate global gene expression profiles regarding the winter survival of Agropyron mongolicum. A genome-wide gene expression analysis involving four different periods was identified. Twenty-eight coexpression modules with distinct patterns were performed for transcriptome profiling. Furthermore, differentially expressed genes (DEGs) and their functional characterization were defined using a genome database such as NT, NR, COG, and KEGG.

RESULT

A total of 79.6% of the unigenes were characterized to be involved in 136 metabolic pathways. In addition, the expression level of ABA receptor genes, regulation of transcription factors, and a coexpression network analysis were conducted using transcriptome data. We found that ABA receptors regulated downstream gene expression by activating bZIP and NAC transcription factors to improve cold resistance and winter survival.

CONCLUSION

This study provides comprehensive transcriptome data for the characterization of overwintering-related gene expression profiles in A. mongolicum. Genomics resources can help provide a better understanding of the overwintering mechanism for perennial gramineae species. By analyzing genome-wide expression patterns for the four key stages of tiller bud development, the functional characteristics of the DEGs were identified that participated in various metabolic pathways and have been shown to be strongly associated with cold tolerance. These results can be further exploited to determine the mechanism of overwintering in perennial gramineae species.

Identification of a novel bZIP transcription factor in Camellia sinensis as a negative regulator of freezing tolerance in transgenic arabidopsis

BACKGROUND AND AIMS

Basic region/leucine zipper (bZIP) transcription factors play vital roles in the abiotic stress response of plants. However, little is known about the function of bZIP genes in Camellia sinensis .

METHODS

CsbZIP6 was overexpressed in Arabidopsis thaliana . Effects of CsbZIP6 overexpression on abscisic acid (ABA) sensitivity, freezing tolerance and the expression of cold-responsive genes in arabidopsis were studied.

KEY RESULTS

CsbZIP6 was induced during cold acclimation in tea plant. Constitutive overexpression of CsbZIP6 in arabidopsis lowered the plants' tolerance to freezing stress and ABA exposure during seedling growth. Compared with wild-type (WT) plants, CsbZIP6 overexpression (OE) lines exhibited increased levels of electrolyte leakage (EL) and malondialdehyde (MDA) contents, and reduced levels of total soluble sugars (TSS) under cold stress conditions. Microarray analysis of transgenic arabidopsis revealed that many differentially expressed genes (DEGs) between OE lines and WT plants could be mapped to 'response to cold' and 'response to water deprivation' terms based on Gene Ontology analysis. Interestingly, CsbZIP6 overexpression repressed most of the cold- and drought-responsive genes as well as starch metabolism under cold stress conditions.

CONCLUSIONS

The data suggest that CsbZIP6 functions as a negative regulator of the cold stress response in A. thaliana , potentially by down-regulating cold-responsive genes.

Stress-responsive gene RsICE1 from Raphanus sativus increases cold tolerance in rice

The ICE1 transcription factor plays a critical role in plant cold tolerance via triggering CBF/DREB1 cold-regulated signal networks. In this work, a novel MYC-type ICE1-like gene, RsICE1, was isolated from radish (Raphanus sativus L.), and its function in cold tolerance was characterized in rice. The RsICE1 gene was expressed constitutively with higher transcriptional levels in the roots and stems of radish seedlings. The NaCl, cold, and ABA treatments could significantly upregulate RsICE1 expression levels, but dehydration stress had a weak effect on its expression. Ectopic expression of the RsICE1 gene in rice conferred enhanced tolerance to low-temperature stress grounded on a higher survival rate, higher accumulation of soluble sugars and free proline content, a decline in electrolyte leakage and MDA levels, and higher chlorophyll levels relative to control plants. OsDREBL and OsTPP1, downstream cold-regulated genes, were remarkably upregulated at transcription levels in rice overexpressing RsICE1 under low-temperature stress, which indicated that RsICE1 was involved in CBF/DREB1 cold-regulated signal networks. Overall, the above data showed that RsICE1 played an active role in improving rice cold tolerance, most likely resulting from the upregulation of OsDREBL and OsTPP1 expression levels by interacting with the RsICE1 gene under low-temperature stress.