Low-temperature stress significantly impacts plant growth, development, yield, and geographical distribution. However, during the long-term process of evolution, plants have evolved complicated mechanisms to resist low-temperature stress. The cold tolerance trait is regulated by multiple pathways, such as the Ca²⁺ signaling cascade, mitogen-activated protein kinase (MAPK) cascade, inducer of CBF expression 1 (ICE1)-C-repeat binding factor (CBF)-cold-reulated gene (COR) transcriptional cascade, reactive oxygen species (ROS) homeostasis regulation, and plant hormone signaling. However, the specific responses of these pathways to cold stress and their interactions are not fully understood. This review summarizes the response mechanisms of plants to cold stress from four aspects, including cold signal perception and transduction, ICE1-CBF-COR transcription cascade regulation, ROS homeostasis regulation and plant hormone signal regulation. It also elucidates the mechanism of cold stress perception and Ca²⁺ signal transduction in plants, and proposes the important roles of transcription factors (TFs), post-translational modifications (PTMs), light signals, circadian clock factors, and interaction proteins in the ICE1-CBF-COR transcription cascade. Additionally, we analyze the importance of ROS homeostasis and plant hormone signaling pathways in plant cold stress response, and explore the cross interconnections among the ICE1-CBF-COR cascade, ROS homeostasis, and plant hormone signaling. This comprehensive review enhances our understanding of the mechanism of plant cold tolerance and provides a molecular basis for genetic strategies to improve plant cold tolerance.

Plant endophytic microorganisms, which can enhance plant growth and resistance to biotic and abiotic stresses, are untapped resources with large potential applications for crop production. However, the endophytic community is influenced by multiple factors, such as host genetics, the environment, and other microbes. Thus, it is important to characterize well-adapted endophytes from native crops. We isolated 43 endophytic bacteria from sugarcane cultivar Yunzhe-99-91. All these 43 isolates were examined in vitro for nitrogenase activity and the ability to dissolve phosphorus and produce siderophore. One of these strains, B9, identified as Bacillussubtilis and showed maximum plant growth promotion, was selected for detailed studies. B9 promoted the production of organic acids such as propionic acid, acetic acid, malic acid and citric acid, and the production of phytohormones, including indole-3-acetic acid, cytokinin, 6-benzyladenine, and zeatin. Moreover, B9 significantly promoted the growth of sugarcane plantlets and increased the content of nitrogen, phosphorus, and potassium in the seedlings by 29.26%, 50.78%, and 15.49%, respectively. The photosynthetic rate, root development, and chlorophyll content were also improved with varying degrees compared to the non-inoculated control. The cotyledon and hypocotyl of sugarcane gems germinated faster when co-cultured with the B9 strain compared with control group. Colonization assay showed that B9 was mainly colonized in the roots, followed by the stems and leaves. In conclusion, the positive interaction between endophytic strain B9 and sugarcane may provide long-lasting benefits and a direction for developing and utilizing B9 as a biofertilizer for sugarcane cultivation to decrease fertilizer application.

Introduction: Sugarcane is one of the most important sugar crops worldwide, however, sugarcane production is seriously limited by sugarcane red rot, a soil-borne disease caused by Colletotrichum falcatum. Bacillus velezensis YC89 was isolated from sugarcane leaves and can significantly inhibited red rot disease caused by C. falcatum.Methods: In this study, the genome of YC89 strain was sequenced, its genome structure and function were analyzed using various bioinformatics software, and its genome was compared with those of other homologous strains. In addition, the effectiveness of YC89 against sugarcane red rot and the evaluation of sugarcane plant growth promotion were also investigated by pot experiments.Results: Here, we present the complete genome sequence of YC89, which consists of a 3.95 Mb circular chromosome with an average GC content of 46.62%. The phylogenetic tree indicated that YC89 is closely related to B. velezensis GS-1. Comparative genome analysis of YC89 with other published strains (B. velezensis FZB42, B. velezensis CC09, B. velezensis SQR9, B. velezensis GS-1, and B. amyloliquefaciens DSM7) revealed that the strains had a part common coding sequences (CDS) in whereas 42 coding were unique of strain YC89. Whole-genome sequencing revealed 547 carbohydrate-active enzymes and identified 12 gene clusters encoding secondary metabolites. Additionally, functional analysis of the genome revealed numerous gene/gene clusters involved in plant growth promotion, antibiotic resistance, and resistance inducer synthesis. In vitro pot tests indicated that YC89 strain controlled sugarcane red rot and promoted the growth of sugarcane plants. Additionally, it increased the activity of enzymes involved in plant defense, such as superoxide dismutase, peroxidase, polyphenol oxidase, chitinase, and β-1,3-glucanase.Discussion: These findings will be helpful for further studies on the mechanisms of plant growth promotion and biocontrol by B. velezensis and provide an effective strategy for controlling red rot in sugarcane plants.

Polyploid Saccharum with complex genomes hindered the progress of sugarcane improvement, while their chloroplast genomes are much smaller and simpler. Chloroplast (cp), the vital organelle, is the site of plant photosynthesis, which also evolves other functions, such as tolerance to environmental stresses. In this study, the cp genome of two sugarcane ancestors Saccharum officinarum and S. spontaneum were sequenced, and genome comparative analysis between these two species was carried out, together with the photosynthetic ability. The length is 141,187 bp for S. officinarum and that is 7 bp longer than S. spontaneum, with the same GC content (38.44%) and annotated gene number (134), 13 with introns among them. There is a typical tetrad structure, including LSC, SSC, IRb and IRa. Of them, LSC and IRa/IRb are 18 bp longer and 6 bp shorter than those in S. spontaneum (83,047 bp and 22,795 bp), respectively, while the size of SSC is same (12,544 bp). Five genes exhibit contraction and expansion at the IR junctions, but only one gene ndhF with 29 bp expansion at the border of IRb/SSC. Nucleotide diversity (Pi) based on sliding window analysis showed that the single copy and noncoding regions were more divergent than IR- and coding regions, and the variant hotspots trnG-trnM, psbM-petN, trnR-rps14, ndhC-trnV and petA-psbJ in the LSC and trnL-ccsA in the SSC regions were detected, and petA-psbJ with the highest divergent value of 0.01500. Genetic distances of 65 protein genes vary from 0.00000 to 0.00288 between two species, and the selective pressure on them indicated that only petB was subjected to positive selection, while more genes including rpoC2, rps3, ccsA, ndhA, ndhA, psbI, atpH and psaC were subjected to purifying or very strong purifying selection. There are larger number of codons in S. spontaneum than that in S. officinarum, while both species have obvious codon preference and the codons with highest-(AUG) and lowest frequency (AUA) are same. Whilst, the most abundant amino acid is leucine in both S. officinarum and S. spontaneum, with number of 2175 (10.88% of total) and 2228 (10.90% of total) codons, respectively, and the lowest number is cysteine, with only 221 (1.105%) and 224 (1.096%), respectively. Protein collinearity analysis showed the high collinearity though several divergences were present in cp genomes, and identification of simple sequence repeats (SSRs) were included in this study. In addition, in order to compare cold tolerance and explore the expanding function of this environmental stress, the chlorophyll relative content (SPAD) and chlorophyll fluorescence Fv/Fm were measured. The significantly higher SPAD were observed in S. spontaneum than those in S. officinarum, no matter what the control conditions, exposure to low temperature or during recovery, and so was for Fv/Fm under exposure to low temperature, together with higher level of SPAD in S. spontaneum in each measurement. Aforementioned results suggest much stronger photosynthetic ability and cold tolerance in S. spontaneum. Our findings build a foundation to investigate the biological mechanism of two sugarcane ancestor chloroplasts and retrieve reliable molecular resources for phylogenetic and evolutionary studies, and will be conducive to genetic improvement of photosynthetic ability and cold resistance in modern sugarcane.