Cloning and cold-resistance analyses of CfICE1 gene in Cryptomeria fortunei

Functions of Basic Helix-Loop-Helix (bHLH) Proteins in the Regulation of Plant Responses to Cold, Drought, Salt, and Iron Deficiency: A Comprehensive Review

Abiotic stresses including cold, drought, salt, and iron deficiency severely impair plant development, crop productivity, and geographic distribution. Several bodies of research have shed light on the pleiotropic functions of BASIC HELIX-LOOP-HELIX (bHLH) proteins in plant responses to these abiotic stresses. In this review, we mention the regulatory roles of bHLH TFs in response to stresses such as cold, drought, salt resistance, and iron deficiency, as well as in enhancing grain yield in plants, especially crops. The bHLH proteins bind to E/G-box motifs in the target promoter and interact with various other factors to form a complex regulatory network. Through this network, they cooperatively activate or repress the transcription of downstream genes, thereby regulating various stress responses. Finally, we present some perspectives for future research focusing on the molecular mechanisms that integrate and coordinate these abiotic stresses. Understanding these molecular mechanisms is crucial for the development of stress-tolerant crops.

Cloning of TaeRF1 gene from Caucasian clover and its functional analysis responding to low-temperature stress

Low temperature (LT) is an important threat to the normal growth of plants. In this study, based on the full-length transcriptome sequencing results, the cold resistance genes were cloned from Caucasian clover with strong cold resistance. We cloned the CDS of TaeRF1, which is 1311 bp in length and encodes 436 amino acids. The molecular weight of the protein is 48.97 kDa, which had no transmembrane structure, and its isoelectric point (pI) was 5.42. We predicted the structure of TaeRF1 and found 29 phosphorylation sites. Subcellular localization showed that TaeRF1 was localized and expressed in cell membrane and chloroplasts. The TaeRF1 gene was induced by stress due to cold, salt, alkali and drought and its expression level was higher in roots and it was more sensitive to LT. Analysis of transgenic A. thaliana plants before and after LT treatment showed that the TaeRF1 gene enhanced the removal of excess H₂O₂, and increased the activity of antioxidant enzymes, thus improving the plant's ability to resist stress. Additionally, the OE lines showed increased cold tolerance by upregulating the transcription level of cold-responsive genes (CBF1, CBF2, COR15B, COR47, ICE1, and RD29A). This study demonstrates that TaeRF1 is actively involved in the responses of plants to LT stress. We also provide a theoretical basis for breeding and a potential mechanism underlying the responses of Caucasian clover to abiotic stress.

MbICE1 Confers Drought and Cold Tolerance through Up-Regulating Antioxidant Capacity and Stress-Resistant Genes in Arabidopsis thaliana

Malus baccata (L.) Borkh is an apple rootstock with good drought and cold resistance. The ICE gene is a key factor in the molecular mechanisms of plant drought and cold resistance. In the present research, the function of drought- and cold-induced MbICE1 of Malus baccata was investigated in Arabidopsis. According to GFP fluorescence images, MbICE1 was determined to be a nuclear protein. The MbICE1 was transferred to Arabidopsis, showing enhanced tolerance to drought and cold stresses. Under drought and cold treatments, the transgenic Arabidopsis had higher chlorophyll content and free proline content than WT plants, but the Malondialdehyde (MDA) content and electrolyte leakage (EL) were lower than those of WT plants. In addition, drought and cold led to a large accumulation of ROS (H₂O₂ and O^2-) content in Arabidopsis, while overexpression of MbICE1 enhanced the antioxidant enzyme activity in Arabidopsis and improved the plant's resistance to stresses. Moreover, the accumulation of MbICE1 promoted the expression of AtCBF1, AtCBF2, AtCBF3, AtCOR15a, AtCOR47 and AtKIN1 genes in Arabidopsis. These data indicate that MbICE1 is a key regulator of drought and cold and can be used as a backup gene for breeding Malus rootstocks.

Overexpression of CfICE1 from Cryptomeria fortunei Enhances Cold, Drought and Salt Stress in Poplar

ICE1, a regulator of the cold-inducible transcriptome and freezing tolerance, is currently widely believed to be involved in plant resistance to cold stress. In this study, CfICE1 from Cryptomeria fortunei was transformed into poplar. Physiological indicators of transgenic, empty vector and wild-type poplar after abiotic stress (cold, drought and salt) were determined. Transgenic lines had a higher chlorophyll content, antioxidant enzyme activity and soluble protein content, as well as a lower malondialdehyde and hydrogen peroxide content. The ultrastructure of the plant was observed by transmission electron microscopy, and after stress, the cell structure of the transgenic line was more complete than that of the wild type. CfICE1 was upregulated in transgenic poplar trees after abiotic stress (cold, drought and salt). The CfICE1 transgenic plants improved plant resistance by regulating the CBF gene of poplar under cold and salt stress. In terms of plant responses to abiotic stress, this study showed that overexpression of CfICE1 improved the cold, drought and salt tolerance of poplars.

Genomic Survey and Cold-Induced Expression Patterns of bHLH Transcription Factors in Liriodendron chinense (Hemsl) Sarg

bHLH transcription factors play an animated role in the plant kingdom during growth and development, and responses to various abiotic stress. In this current study, we conducted, the genome-wide survey of bHLH transcription factors in Liriodendron chinense (Hemsl) Sarg., 91 LcbHLH family members were identified. Identified LcbHLH gene family members were grouped into 19 different subfamilies based on the conserved motifs and phylogenetic analysis. Our results showed that LcbHLH genes clustered in the same subfamily exhibited a similar conservative exon-intron pattern. Hydrophilicity value analysis showed that all LcbHLH proteins were hydrophilic. The Molecular weight (Mw) of LcbHLH proteins ranged from 10.19 kD (LcbHLH15) to 88.40 kD (LcbHLH50). A greater proportion, ~63%, of LcbHLH proteins had a theoretical isoelectric point (pI) less than seven. Additional analysis on the collinear relationships within species and among dissimilar species illustrated that tandem and fragment duplication are the foremost factors of amplification of this family in the evolution process, and they are all purified and selected. RNA-seq and real-time quantitative PCR analysis of LcbHLH members showed that the expression of LcbHLH35, 55, and 86 are up-regulated, and the expression of LcbHLH9, 20, 39, 54, 56, and 69 is down-regulated during cold stress treatments while the expression of LcbHLH24 was up-regulated in the short term and then later down-regulated. From our results, we concluded that LcbHLH genes might participate in cold-responsive processes of L. chinense. These findings provide the basic information of bHLH gene in L. chinense and their regulatory roles in plant development and cold stress response.

CfAPX, a cytosolic ascorbate peroxidase gene from Cryptomeria fortunei, confers tolerance to abiotic stress in transgenic Arabidopsis

Plants subjected to biotic or abiotic stresses produce a large amount of reactive oxygen species (ROS). If ROS cannot be cleared in time, they cause a series of harmful reactions in plants. Ascorbate peroxidase (APX) is a key enzyme that removes ROS from plant cells and plays a vital role in plant stress resistance. However, to date, no studies on APX homologs in Cryptomeria fortunei have been reported. In this study, we isolated complementary DNA (cDNA) encoding APXfrom C. fortunei needles, which is referred to as CfAPX, by rapid amplification of cDNA ends (RACE). The full-length CfAPX sequence was 1226 bp in length and included a 750-bp open reading frame (ORF) encoding a protein of 249 amino acids. Phylogenetic analysis showed that APXs of different plant species have been highly evolutionarily conserved. CfAPX was shown to belong to the cytoplasmic subgroup and was more closely related to GbAPX of the gymnosperm Ginkgo biloba. CfAPX showed no transcriptional activity in yeast cells but was highly expressed in cones. To better handle abiotic stresses, compared with wild-type (WT) Arabidopsis thaliana, 35S::CfAPX transgenic Arabidopsis strongly expressed CfAPX, presented increased antioxidant enzyme activities, ascorbic acid (AsA) contents, chlorophyll levels and fluorescence parameter and reduced malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents. In addition, CfAPX expression in C. fortunei was mostly upregulated under stress. In summary, CfAPX confers abiotic stress responses to plants, which provides a scientific basis for subsequent breeding for increased stress resistance in C. fortunei.