Jasmonate biosynthesis enzyme allene oxide cyclase 2 mediates cold tolerance and pathogen resistance.

Allene oxide cyclase (AOC) is a key enzyme in the biosynthesis of jasmonic acid (JA), which is involved in plant growth and development as well as adaptation to environmental stresses. We identified the cold- and pathogen-responsive AOC2 gene from Medicago sativa subsp. falcata (MfAOC2) and its homolog MtAOC2 from Medicago truncatula. Heterologous expression of MfAOC2 in M. truncatula enhanced cold tolerance and resistance to the fungal pathogen Rhizoctonia solani, with greater accumulation of JA and higher transcript levels of JA downstream genes than in wild-type plants. In contrast, mutation of MtAOC2 reduced cold tolerance and pathogen resistance, with less accumulation of JA and lower transcript levels of JA downstream genes in the aoc2 mutant than in wild-type plants. The aoc2 phenotype and low levels of cold-responsive C-repeat-binding factor (CBF) transcripts could be rescued by expressing MfAOC2 in aoc2 plants or exogenous application of methyl jasmonate. Compared with wild-type plants, higher levels of CBF transcripts were observed in lines expressing MfAOC2 but lower levels of CBF transcripts were observed in the aoc2 mutant under cold conditions; superoxide dismutase, catalase, and ascorbate-peroxidase activities as well as proline concentrations were higher in MfAOC2-expressing lines but lower in the aoc2 mutant. These results suggest that expression of MfAOC2 or MtAOC2 promotes biosynthesis of JA, which positively regulates expression of CBF genes and antioxidant defense under cold conditions and expression of JA downstream genes after pathogen infection, leading to greater cold tolerance and pathogen resistance.

Transcriptomic analysis revealed the candidate metabolic pathways and genes associated with cold tolerance in a mutant without anthocyanin accumulation in common vetch (Vicia sativa L.).

Common vetch (Vicia sativa L.) is a leguminous crop used to feed livestock with vegetative organs or fertilize soils by returning to the field. Survival of fall-seeded plants is often affected by freezing damage during overwintering. This study aims to investigate the transcriptomic profiling in response to cold in a mutant with reduced accumulation of anthocyanins under normal growth and low-temperature conditions for understanding the underlying mechanisms. The mutant had increased cold a tolerance with higher survival rate and biomass during overwintering compared to the wild type, which led to increased forage production. Transcriptomic analysis in combination with qRT-PCR and physiological measurements revealed that reduced anthocyanins accumulation in the mutant resulted from reduced expression of serial genes involving in anthocyanin biosynthesis, which led to the altered metabolism, with an increased accumulation of free amino acids and polyamines. The higher levels of free amino acids and proline in the mutant under low temperature were associated with improved cold tolerance. The altered expression of some genes involved in ABA and GA signaling was also associated with increased cold tolerance in the mutant.

Accurate Estimation of Single-Cell Differentiation Potency Based on Network Topology and Gene Ontology Information.

One important task in single-cell analysis is to quantify the differentiation potential of single cells. Though various single-cell potency measures have been proposed, they are based on individual biological sources, thus not robust and reliable. It is still a challenge to combine multiple sources to generate a relatively reliable and robust measure to estimate differentiation. In this paper, we propose a New Centrality measure with Gene ontology information (NCG) to estimate single-cell potency. NCG is designed by combining network topology property with edge clustering coefficient, and gene function information using gene ontology function similarity scores. NCG distinguishes pluripotent cells from non-pluripotent cells with high accuracy, correctly ranks different cell types by their differentiation potency, tracks changes during the differentiation process, and constructs the lineage trajectory from human myoblasts into skeletal muscle cells. These indicate that NCG is a reliable and robust measure to estimate single-cell potency. NCG is anticipated to be a useful tool for identifying novel stem or progenitor cell phenotypes from single-cell RNA-Seq data. The source codes and datasets are available at https://github.com/Xinzhe-Ni/NCG.

A novel LRR-RLK (CTLK) confers cold tolerance through regulation on the C-repeat-binding factor pathway, antioxidants, and proline accumulation.

Leucine-rich repeat-receptor-like kinase (LRR-RLK) is a large subfamily of plant RLKs; however, its role in cold tolerance is still unknown. A novel cold tolerance LRR-RLK gene (MtCTLK1) in Medicago truncatula was identified using the transgenic lines overexpressing MtCTLK1 (MtCTLK1-OE) and mtctlk1 lines with Tnt1 retrotransposon insertion. Compared with the wild-type, MtCTLK1-OE lines had increased cold tolerance and mtctlk1 showed decreased cold tolerance. The impaired cold tolerance in mtctlk1 could be complemented by the transgenic expression of MtCTLK1 or its homolog MfCTLK1 from Medicago falcata. Antioxidant enzyme activities and proline accumulation as well as transcript levels of the associated genes were increased in response to cold, with higher levels in MtCTLK1-OE or lower levels in mtctlk1 lines as compared with wild type. C-Repeat-Binding Factors (CBFs) and CBF-dependent cold-responsive genes were also induced in response to cold, and higher transcript levels of CBFs and CBF-dependent cold-responsive genes were observed in MtCTLK1-OE lines whereas lower levels in mtctlk1 mutants. The results validate the role of MtCTLK1 or MfCTLK1 in the regulation of cold tolerance through the CBF pathway, antioxidant defense system and proline accumulation. It also provides a valuable gene for the molecular breeding program to improve cold tolerance in crops.