Involvement of microRNA164 in responses to heat stress in Arabidopsis

microRNA regulates cytokinin induced parthenocarpy in cucumber (Cucumis sativus L.)

Parthenocarpy is one of the most important agronomic traits for fruit yield in cucumbers. However, the precise gene regulation and the posttranscriptional mechanism are elusive. In the presented study, one parthenocarpic line DDX and non-parthenocarpic line ZK were applied to identify the microRNAs (miRNAs) involved in parthenocarpic fruit formation. The differential expressed miRNAs among parthenocarpic fruit of forchlorfenuron (CPPU) treated ZK (ZK-CPPU), pollinated ZK (ZK-P), non-pollinated DDX (DDX-NP) were compared with the non-parthenocarpic fruits of non-pollinated ZK (ZK-NP). It indicated 98 miRNAs exhibited differential expression were identified. Notably, a significant proportion of these miRNAs were enriched in the signal transduction pathway of plant hormones, as identified by the KEGG pathway analysis. qRT-PCR validation indicated that CsmiR156 family was upregulated in the ZK-NP while downregulated in ZK-CPPU, ZK-P, and DDX-NP at 1 day after anthesis. Meanwhile, the opposite trend was observed for CsmiR164a. In ZK-CPPU, ZK-P, and DDX-NP, CsmiRNA156 genes (CsSPL16 and CsARR9-like) were upregulated while CsmiRNA164a genes (CsNAC6, CsCUC1, and CsNAC100) were downregulated. The GUS and dual luciferase assay validated that CsmiR156a inhibited while CsmiR164a induced their target genes' transcription. This study presents novel insights into the involvement of CsmiR156a and CsmiR164a in the CK-mediated posttranscriptional regulation of cucumber parthenocarpy, which will aid future breeding programs.

The Emerging Role of Non-Coding RNAs (ncRNAs) in Plant Growth, Development, and Stress Response Signaling

Plant species utilize a variety of regulatory mechanisms to ensure sustainable productivity. Within this intricate framework, numerous non-coding RNAs (ncRNAs) play a crucial regulatory role in plant biology, surpassing the essential functions of RNA molecules as messengers, ribosomal, and transfer RNAs. ncRNAs represent an emerging class of regulators, operating directly in the form of small interfering RNAs (siRNAs), microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs). These ncRNAs exert control at various levels, including transcription, post-transcription, translation, and epigenetic. Furthermore, they interact with each other, contributing to a variety of biological processes and mechanisms associated with stress resilience. This review primarily concentrates on the recent advancements in plant ncRNAs, delineating their functions in growth and development across various organs such as root, leaf, seed/endosperm, and seed nutrient development. Additionally, this review broadens its scope by examining the role of ncRNAs in response to environmental stresses such as drought, salt, flood, heat, and cold in plants. This compilation offers updated information and insights to guide the characterization of the potential functions of ncRNAs in plant growth, development, and stress resilience in future research.

BcWRKY22 Activates BcCAT2 to Enhance Catalase (CAT) Activity and Reduce Hydrogen Peroxide (H2O2) Accumulation, Promoting Thermotolerance in Non-Heading Chinese Cabbage (Brassica campestris ssp. chinensis)

WRKY transcription factors (TFs) participate in plant defense mechanisms against biological and abiotic stresses. However, their regulatory role in heat resistance is still unclear in non-heading Chinese cabbage. Here, we identified the WRKY-IIe gene BcWRKY22(BraC09g001080.1), which is activated under high temperatures and plays an active role in regulating thermal stability, through transcriptome analysis. We further discovered that the BcWRKY22 protein is located in the nucleus and demonstrates transactivation activity in both the yeast and plant. Additionally, our studies showed that the transient overexpression of BcWRKY22 in non-heading Chinese cabbage activates the expression of catalase 2 (BcCAT2), enhances CAT enzyme activity, and reduces Hydrogen Peroxide (H2O2) accumulation under heat stress conditions. In addition, compared to its wild-type (WT) counterparts, Arabidopsis thaliana heterologously overexpresses BcWRKY22, improving thermotolerance. When the BcWRKY22 transgenic root was obtained, under heat stress, the accumulation of H2O2 was reduced, while the expression of catalase 2 (BcCAT2) was upregulated, thereby enhancing CAT enzyme activity. Further analysis revealed that BcWRKY22 directly activates the expression of BcCAT2 (BraC08g016240.1) by binding to the W-box element distributed within the promoter region of BcCAT2. Collectively, our findings suggest that BcWRKY22 may serve as a novel regulator of the heat stress response in non-heading Chinese cabbage, actively contributing to the establishment of thermal tolerance by upregulating catalase (CAT) activity and downregulating H2O2 accumulation via BcCAT2 expression.

Regulatory roles of microRNA163 in responses to stresses in Arabidopsis

MicroRNAs (miRNAs) are small regulatory RNAs that participate in various biological processes by silencing target genes. In Arabidopsis, microRNA163 (miR163) was found to be involved in seed germination, root development, and biotic resistance. However, the regulatory roles of miR163 remain unclear. In the current study, the mir163 mutant was investigated to comprehensively understand and characterize its functions in Arabidopsis. RNA-sequencing and Gene Ontology enrichment analyses revealed that miR163 might be involved in "response to stimulus" and "metabolic process". Interestingly, "response to stress", including heat, cold, and oxidative stress, was enriched under the subcategory of "response to stimulus". We observed that miR163 and PXMT were repressed and induced under heat stress, respectively. Furthermore, the study detected significant differences in seed germination rate, hypocotyl length, and survival rate, indicating a variation in the thermotolerance between WT and mir163 mutant. The results revealed that the mir163 mutant had a lesser degree of germination inhibition by heat treatment than WT. In addition, the mir163 mutant showed a better survival rate and longer hypocotyl length under heat treatment than the WT. The metabolomes of WT and mir163 mutant were further analyzed. The contents of benzene derivatives and flavonoids were affected by miR163, which could enhance plants' defense abilities. In conclusion, miR163/targets regulated the expression of stress-responsive genes and the accumulation of defense-related metabolites to alter stress tolerance.