Circular RNAs (circRNAs) are a type of newly identified non-coding RNAs through high-throughput deep sequencing, which play important roles in miRNA function and transcriptional controlling in human, animals, and plants. To date, there is no report in wheat seedlings regarding the circRNAs identification and roles in the dehydration stress response. In present study, the total RNA was extracted from leaves of wheat seedlings under dehydration-stressed and well-watered conditions, respectively. Then, the circRNAs enriched library based deep sequencing was performed and the circRNAs were identified using bioinformatics tools. Around 88 circRNAs candidates were isolated in wheat seedlings leaves while 62 were differentially expressed in dehydration-stressed seedlings compared to well-watered control. Among the dehydration responsive circRNAs, six were found to act as 26 corresponding miRNAs sponges in wheat. Sixteen circRNAs including the 6 miRNAs sponges and other 10 randomly selected ones were further validated to be circular by real-time PCR assay, and 14 displayed consistent regulation patterns with the transcriptome sequencing results. After Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the targeted mRNAs functions, the circRNAs were predicted to be involved in dehydration responsive process, such as photosynthesis, porphyrin, and chlorophyll metabolism, oxidative phosphorylation, amino acid biosynthesis, and metabolism, as well as plant hormone signal transduction, involving auxin, brassinosteroid, and salicylic acid. Herein, we revealed a possible connection between the regulations of circRNAs with the expressions of functional genes in wheat leaves associated with dehydration resistance.

The compound 5-aminolevulinic acid (ALA) is an essential precursor for the biosynthesis of porphyrins, including chlorophyll, heme, and cytochromes. The protective effects of ALA on photosynthesis and the expression of photosynthetic genes in wheat under drought stress are not well understood. Two wheat cultivars, drought-tolerant Aikang-58 and droughtsensitive Chinese Spring, were exposed to drought stress induced by 20% polyethylene glycol (PEG-6000) after foliar pretreatment with ALA for 3 days. The results showed that exogenous application of ALA protected the drought-stressed wheat seedlings by significantly inhibiting the decrease in relative water and chlorophyll contents. The ALA-mediated alleviation of stress was similar between the drought-tolerant and drought-sensitive wheat cultivars. Meanwhile, compared to seedlings under drought treatment alone, the ALA-pre-treated wheat seedlings under drought stress maintained higher photosystem II (PSII) functional indexes. The ALA pretreatment reduced the drought-driven accumulation of both H 2 O 2 and ABA and increased the stomatal conductance. Real-time PCR analysis showed that the psbA and psbD gene transcripts were both upregulated under drought stress following ALA pretreatment. The present study suggests that the exogenous foliar application of ALA alleviates the drought stress on wheat seedlings, which is associated with the enhancement of PSII function by inducing chlorophyll synthesis and psbA and psbD transcription. Moreover, the protective effect of ALA pretreatment was not related to the decline in stomatal conductance caused by ABA or H 2 O 2 accumulation.

Backgrounds: The perturbance of chloroplast proteins is a major cause of photosynthesis inhibition under drought stress. The exogenous application of 5-aminolevulinic acid (ALA) mitigates the damage caused by drought stress, protecting plant growth and development, but the regulatory mechanism behind this process remains obscure.Results: Wheat seedlings were drought treated, and the iTRAQ-based proteomic approach was employed to assess the difference in chloroplast protein content caused by exogenous ALA. A total of 9499 peptides, which could be classified into 2442 protein groups, were identified with ≤0.01 FDR. Moreover, the contents of 87 chloroplast proteins was changed by drought stress alone compared to that of the drought-free control, while the contents of 469 was changed by exogenous ALA application under drought stress compared to that of drought stress alone. The Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results suggested that the ALA pretreatment adjusted some biological pathways, such as metabolic pathways and pathways involved in photosynthesis and ribosomes, to enhance the drought resistance of chloroplasts. Furthermore, the drought-promoted H 2 O 2 accumulation and O 2 − production in chloroplasts were alleviated by the exogenous pretreatment of ALA, while peroxidase (POD) and glutathione peroxidase (GPX) activities were upregulated, which agreed with the chloroplast proteomic data. We suggested that ALA promoted reactive oxygen species (ROS) scavenging in chloroplasts by regulating enzymatic processes. Conclusions:Our results from chloroplast proteomics extend the understanding of the mechanisms employed by exogenous ALA to defend against drought stress in wheat.