Study the effect of 24-epibrassinolide application on the Cu/Zn-SOD expression and tolerance to drought stress in common bean.

To study the possibility of increasing the drought tolerance of common bean with the exogenous application of 24-epibrassinolide (EBL), an experiment was conducted in 2016 and 2017. In this experiment, two irrigation levels (optimal irrigation and drought stress) were applied to the main plots and two common bean genotypes (Kusha cultivar and COS16 genotype) and four EBL concentrations (0, 2, 4, and 6 µM) were allocated to sub-plots as factorial. In the flowering stage, drought stress was applied and plants were sprayed with EBL. The results showed that drought stress reduced relative water content (RWC) and increased proline content, malondialdehyde (MDA) content, and antioxidant enzymes activity. However, exogenous application of EBL reduced the seed yield loss and increased the drought stress tolerance in both common bean genotypes by decreasing the MDA content and increasing the RWC, proline content, antioxidant enzymes activity, and nitrate reductase activity. It can be concluded that foliar spray of 4 µM EBL as the best concentration may increase the seed yield and enhance the drought stress tolerance of common bean. Also, Cu/Zn-SOD was up-regulated in response to the drought stress and exogenous EBL. The COS16 genotype showed better response to the drought stress and exogenous EBL than the Kusha cultivar, because of the higher up-regulation of Cu/Zn-SOD in this genotype compared to the Kusha cultivar. Therefore, EBL can be used as a plant growth regulator to enhance drought stress tolerance and minimize the seed yield loss of common bean caused by water deficit.

MicroRNA Signatures of Drought Signaling in Rice Root.

BACKGROUND: Drought stress is one of the most important abiotic stresses and the main constraint to rice agriculture. MicroRNA-mediated post-transcriptional gene regulation is one of the ways to establish drought stress tolerance in plants. MiRNAs are 20-24-nt regulatory RNAs that play an important role in regulating plant gene expression upon exposure to biotic and abiotic stresses. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we applied a partial root drying system as well as a complete root drying system to identify miRNAs involved in conditions of drought stress, drought signaling and wet signaling using high-throughput sequencing. To this end, we produced four small RNA libraries: (1) fully-watered (WW), (2) fully-droughted (WD), and split-root systems where (3) one-half was well watered (SpWW) and (4) the other half was water-deprived (SpWD). Our analysis revealed 10,671 and 783 unique known and novel miRNA reads in all libraries, respectively. We identified, 65 (52 known + 13 novel), 72 (61 known + 11 novel) and 51 (38 known + 13 novel) miRNAs that showed differential expression under conditions of drought stress, drought signaling and wet signaling, respectively. The results of quantitative real-time PCR showed expression patterns similar to the high-throughput sequencing results. Furthermore, our target prediction led to the identification of 244, 341 and 239 unique target genes for drought-stress-, drought-signaling- and wet-signaling-responsive miRNAs, respectively. CONCLUSIONS/SIGNIFICANCE: Our results suggest that miRNAs that are responsive under different conditions could play different roles in the regulation of abscisic acid signaling, calcium signaling, detoxification and lateral root formation.

Phytoplasma-Responsive microRNAs Modulate Hormonal, Nutritional, and Stress Signalling Pathways in Mexican Lime Trees.

BACKGROUND: Witches' broom disease of Mexican lime (Citrus aurantifolia L.), which is associated to the phytoplasma 'Candidatus Phytoplasma aurantifolia', is a devastating disease that results in significant economic losses. Plants adapt to biotic stresses by regulating gene expression at the transcriptional and post-transcriptional levels. MicroRNAs (miRNAs) are a recently identified family of molecules that regulate plant responses to environmental stresses through post-transcriptional gene silencing. METHODS: Using a high-throughput approach to sequence small RNAs, we compared the expression profiles of miRNAs in healthy Mexican lime trees and in plants infected with 'Ca. P. aurantifolia'. RESULTS: Our results demonstrated the involvement of different miRNAs in the response of Mexican lime trees to infection by 'Ca. P. aurantifolia'. We identified miRNA families that are expressed differentially upon infection with phytoplasmas. Most of the miRNAs had variants with small sequence variations (isomiRs), which are expressed differentially in response to pathogen infection. CONCLUSIONS: It is likely that the miRNAs that are expressed differentially in healthy and phytoplasma-infected Mexican lime trees are involved in coordinating the regulation of hormonal, nutritional, and stress signalling pathways, and the complex interactions between them. Future research to elucidate the roles of these miRNAs should improve our understanding of the level of diversity of specific plant responses to phytoplasmas.