MdbHLH160 is stabilized via reduced MdBT2-mediated degradation to promote MdSOD1 and MdDREB2A-like expression for apple drought tolerance

SlBTB19 interacts with SlWRKY2 to suppress cold tolerance in tomato via the CBF pathway

Cold stress restricts the metabolic and physiological activities of plants, thereby affecting their growth and development. Although broad-complex, tramtrack, and bric-à-brac (BTB) proteins are essential for diverse biological processes and stress responses, the mechanisms underlying BTB-mediated cold responses remain not fully understood. Here, we characterize the function of the cold-induced SlBTB19 protein in tomato (Solanum lycopersicum). Overexpression of SlBTB19 resulted in increased plant sensitivity to cold stress, whereas SlBTB19 knockout mutants exhibited a cold-tolerance phenotype. Further analyses, including protein-protein interaction studies and cell-free degradation assays, revealed that SlBTB19 interacts with and destabilizes the transcription factor SlWRKY2. Using virus-induced gene silencing (VIGS) to silence SlWRKY2 in both wild-type and slbtb19 mutants, we provided genetic evidence that SlWRKY2 acts downstream of SlBTB19 in regulating cold tolerance. Importantly, we demonstrated that SlWRKY2 positively regulates cold tolerance in a CRT/DRE binding factor (CBF)-dependent manner. Under cold stress, SlWRKY2 binds to the W-box in the CBF1 and CBF3 promoters, directly activating their expression. In summary, our findings identify a SlBTB19-SlWRKY2 module that negatively regulates the CBF-dependent cold tolerance pathway in tomato.

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.

Joint transcriptomic and metabolomic analysis provides new insights into drought resistance in watermelon (Citrullus lanatus)

Introduction

Watermelon is an annual vine of the family Cucurbitaceae. Watermelon plants produce a fruit that people love and have important nutritional and economic value. With global warming and deterioration of the ecological environment, abiotic stresses, including drought, have become important factors that impact the yield and quality of watermelon plants. Previous research on watermelon drought resistance has included analyzing homologous genes based on known drought-responsive genes and pathways in other species.

Methods

However, identifying key pathways and genes involved in watermelon drought resistance through high-throughput omics methods is particularly important. In this study, RNA-seq and metabolomic analysis were performed on watermelon plants at five time points (0 h, 1 h, 6 h, 12 h and 24 h) before and after drought stress.

Results

Transcriptomic analysis revealed 7829 differentially expressed genes (DEGs) at the five time points. The DEGs were grouped into five clusters using the k-means clustering algorithm. The functional category for each cluster was annotated based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database; different clusters were associated with different time points after stress. A total of 949 metabolites were divided into 10 categories, with lipids and lipid-like molecules accounting for the most metabolites. Differential expression analysis revealed 22 differentially regulated metabolites (DRMs) among the five time points. Through joint analysis of RNA-seq and metabolome data, the 6-h period was identified as the critical period for watermelon drought resistance, and the starch and sucrose metabolism, plant hormone signal transduction and photosynthesis pathways were identified as important regulatory pathways involved in watermelon drought resistance. In addition, 15 candidate genes associated with watermelon drought resistance were identified through joint RNA-seq and metabolome analysis combined with weighted correlation network analysis (WGCNA). Four of these genes encode transcription factors, including bHLH (Cla97C03G068160), MYB (Cla97C01G002440), HSP (Cla97C02G033390) and GRF (Cla97C02G042620), one key gene in the ABA pathway, SnRK2-4 (Cla97C10G186750), and the GP-2 gene (Cla97C05G105810), which is involved in the starch and sucrose metabolism pathway.

Discussion

In summary, our study provides a theoretical basis for elucidating the molecular mechanisms underlying drought resistance in watermelon plants and provides new genetic resources for the study of drought resistance in this crop.

The transcription factor PbbHLH164 is destabilized by PbRAD23C/D.1 and mediates ethylene biosynthesis during pear fruit ripening

The phytohormone ethylene plays an important role in climacteric fruit ripening. However, the knowledge on molecular regulation of ethylene biosynthesis remains limited in pear fruit. Herein, a new basic helix-loop-helix transcription factor, PbbHLH164, was identified based on the transcriptome analysis of different developing and ripening fruits of two pear cultivars 'Sucui No. 1' and 'Cuiguan'. PbbHLH164 was more highly expressed in ripening fruit than in developing fruit and positively correlated with ethylene production in both cultivars. PbbHLH164 could directly bind to the promoter of 1-aminocyclopropane-1-carboxylate synthase, PbACS1b, to enhance the expression, leading to the increase of ethylene production and the acceleration of fruit ripening. Interestingly, PbbHLH164 physically interacted with an ubiquitin-like/ubiquitin-associated protein PbRAD23C/D.1, and the interaction of PbbHLH164 with PbRAD23C/D.1 attenuated the function of PbbHLH164 in enhancing the activity of the PbACS1b promoter. Notably, PbRAD23C/D.1 was involved in the degradation of PbbHLH164, and this degradation was inhibited by an ubiquitin proteasome inhibitor MG132. Different from PbbHLH164, PbRAD23C/D.1 was more highly expressed in developing fruit than in ripening fruit of both cultivars. These results suggest that the increase of ethylene production during pear fruit ripening results from the up-regulated expression of PbbHLH164 and the down-regulated expression of PbRAD23C/D.1. This information provided new insights into the molecular regulation of ethylene biosynthesis during fruit ripening.