Mechanistic basis for mitigating drought tolerance by selenium application in tobacco (Nicotiana tabacum L.): a multi-omics approach.

The lack of irrigation water in agricultural soils poses a significant constraint on global crop production. In-depth investigation into microRNAs (miRNAs) has been widely used to achieve a comprehensive understanding of plant defense mechanisms. However, there is limited knowledge on the association of miRNAs with drought tolerance in cigar tobacco. In this study, a hydroponic experiment was carried out to identify changes in plant physiological characteristics, miRNA expression and metabolite profile under drought stress, and examine the mitigating effects of selenium (Se) application. The shoot dry weight of drought-stressed plants was approximately half (50.3%) of that in non-stressed (control) conditions. However, plants supplied with Se attained 38.8% greater shoot dry weight as compared to plants with no Se supply under drought stress. Thirteen miRNAs were identified to be associated with drought tolerance. These included 7 known (such as nta-miR156b and nta-miR166a) and 6 novel miRNAs (such as novel-nta-miR156-5p and novel-nta-miR209-5p) with the target genes of squamosa promoter-binding-like protein 4 (SPL4), serine/threonine protein phosphatase 2A (PPP2A), cation/calcium exchanger 4-like (CCX4), extensin-1-like (EXT1) and reduced wall acetylation 2 (RWA2). Further investigation revealed that the expression levels of Ext1 and RWA2 were significantly decreased under drought stress but increased with Se addition. Moreover, key metabolites such as catechin and N-acetylneuraminic acid were identified, which may play a role in the regulation of drought tolerance. The integrated analysis of miRNA sequencing and metabolome highlighted the significance of the novel-nta-miR97-5p- LRR-RLK- catechin pathway in regulating drought tolerance. Our findings provide valuable insights into the molecular mechanisms underlying drought tolerance and Se-induced stress alleviation in cigar tobacco.

miRNA transcriptome reveals key miRNAs and their targets contributing to the difference in Cd tolerance of two contrasting maize genotypes.

Soil cadmium (Cd) contamination is a global environmental and food safety production issue. microRNAs (miRNAs) are proven to be involved in plant growth and development, and abiotic/biotic stress response, but their role in Cd tolerance is largely unknown in maize. To understand the genetic basis of Cd tolerance, two maize genotypes differing in Cd tolerance (L42, a sensitive genotype and L63, a tolerant genotype) were selected, and miRNA sequencing was carried out at nine-day-old seedlings exposed to 24 h Cd stress (5 µM CdCl2). A total of 151 differentially expressed miRNAs were identified, including 20 known miRNAs and 131 novel miRNAs. The results revealed that 90 and 22 miRNAs were up-regulated and down-regulated by Cd in Cd-tolerant genotype L63, and there were 23 and 43 miRNAs in Cd-sensitive genotype L42, respectively. Twenty-six miRNAs were up-regulated in L42 and unchanged or down-regulated in L63, or unchanged in L42 and down-regulated in L63. There were 108 miRNAs that were up-regulated in L63 and unchanged or down-regulated in L42, or unchanged in L63 and down-regulated in L42. Their target genes were enriched mainly in peroxisomes, glutathione (GSH) metabolism, ABC transporter, and ubiquitin-protease system. Among them, target genes involved in the peroxisome pathway and GSH metabolism might play key roles in Cd tolerance in L63. Besides, several ABC transporters which might involve in Cd uptake and transport were identified. The differentially expressed miRNAs or target genes could be used for breeding low grain Cd accumulation and high Cd tolerance cultivars in maize.

Genome-wide association studies and transcriptome sequencing analysis reveal novel genes associated with Al tolerance in wheat.

Aluminum (Al) toxicity is a major threat to the productivity and quality of wheat on acid soil. Identifying novel Al tolerance genes is crucial for breeders to pyramid different tolerance mechanisms thus leading to greater Al tolerance. We aim to identify novel quantitative trait loci (QTL) and key candidate genes associated with Al tolerance in wheat. Herein, we investigated the genotypic variation in Al tolerance among 334 wheat varieties using an acid soil assay. Genome-wide association study (GWAS) and transcriptome were carried out to identify key genes for Al tolerance. GWAS identified several QTL associated with acid soil tolerance including one major QTL on chromosome 1A, in addition to the QTL on 4D where TaALMT1 is located. The four significant markers around the newly identified QTL explained 27.2% of the phenotypic variation. With the existence of reported markers for TaALMT1, more than 97% of the genotypes showed tolerance to Al. For those genotypes with the existence of the novel QTL on 1A but without TaALMT1, more than 90% of genotypes showed medium or high tolerance to Al, confirming the existence of the Al tolerance gene(s) on chromosome 1A. By combining GWAS and RNA-seq analysis, we identified 11 candidate genes associated with Al tolerance. The results provide new insights into the genetic basis of Al tolerance in wheat. The identified genes can be used for the breeding of Al tolerant accessions.