Systematic analysis of differentially expressed ZmMYB genes related to drought stress in maize

ZmC2H2-149 negatively regulates drought tolerance by repressing ZmHSD1 in maize

Drought is a major abiotic stress that limits maize production worldwide. Therefore, it is of great importance to improve drought tolerance in crop plants for sustainable agriculture. In this study, we examined the roles of Cys2 /His2 zinc-finger-proteins (C2H2-ZFPs) in maize's drought tolerance as C2H2-ZFPs have been implicated for plant stress tolerance. By subjecting 150 Ac/Ds mutant lines to drought stress, we successfully identified a Ds-insertion mutant, zmc2h2-149, which shows increased tolerance to drought stress. Overexpression of ZmC2H2-149 in maize led to a decrease in both drought tolerance and crop yield. DAP-Seq, RNA-Seq, Y1H and LUC assays additionally showed that ZmC2H2-149 directly suppresses the expression of a positive drought tolerance regulator, ZmHSD1 (hydroxysteroid dehydrogenase 1). Consistently, the zmhsd1 mutants exhibited decreased drought tolerance and grain yield under water deficit conditions compared to their respective wild-type plants. Our findings thus demonstrated that ZmC2H2-149 can regulate ZmHSD1 for drought stress tolerance in maize, offering valuable theoretical and genetic resources for maize breeding programmes that aim for improving drought tolerance.

Maize-Azospirillum brasilense interaction: accessing maize's miRNA expression under the effect of an inhibitor of indole-3-acetic acid production by the plant

MicroRNA (miRNA) is a class of non-coding RNAs. They play essential roles in plants' physiology, as in the regulation of plant development, response to biotic and abiotic stresses, and symbiotic processes. This work aimed to better understand the importance of maize's miRNA during Azospirillum-plant interaction when the plant indole-3-acetic acid (IAA) production was inhibited with yucasin, an inhibitor of the TAM/YUC pathway. Twelve cDNA libraries from a previous Dual RNA-Seq experiment were used to analyze gene expression using a combined analysis approach. miRNA coding genes (miR) and their predicted mRNA targets were identified among the differentially expressed genes. Statistical differences among the groups indicate that Azospirillum brasilense, yucasin, IAA concentration, or all together could influence the expression of several maize's miRNAs. The miRNA's probable targets were identified, and some of them were observed to be differentially expressed. Dcl4, myb122, myb22, and morf3 mRNAs were probably regulated by their respective miRNAs. Other probable targets were observed responding to the IAA level, the bacterium, or all of them. A. brasilense was able to influence the expression of some maize's miRNA, for example, miR159f, miR164a, miR169j, miR396c, and miR399c. The results allow us to conclude that the bacterium can influence directly or indirectly the expression of some of the identified mRNA targets, probably due to an IAA-independent pathway, and that they are somehow involved in the previously observed physiological effects.

Molecular mechanism analysis of ZmRL6 positively regulating drought stress tolerance in maize

MYB-related genes, a subclass of MYB transcription factor family, have been documented to play important roles in biological processes such as secondary metabolism and stress responses that affect plant growth and development. However, the regulatory roles of MYB-related genes in drought stress response remain unclear in maize. In this study, we discovered that a 1R-MYB gene, ZmRL6, encodes a 96-amino acid protein and is highly drought-inducible. We also found that it is conserved in both barley (Hordeum vulgare L.) and Aegilops tauschii. Furthermore, we observed that overexpression of ZmRL6 can enhance drought tolerance while knock-out of ZmRL6 by CRISPR-Cas9 results in drought hypersensitivity. DAP-seq analyses additionally revealed the ZmRL6 target genes mainly contain ACCGTT, TTACCAAAC and AGCCCGAG motifs in their promoters. By combining RNA-seq and DAP-seq results together, we subsequently identified eight novel target genes of ZmRL6 that are involved in maize's hormone signal transduction, sugar metabolism, lignin synthesis, and redox signaling/oxidative stress. Collectively, our data provided insights into the roles of ZmRL6 in maize's drought response.

Physiological and transcriptome analyses highlight multiple pathways involved in drought stress in Medicago falcata

Medicago falcata is one of the leguminous forage crops, which grows well in arid and semiarid region. To fully investigate the mechanism of drought resistance response in M. falcata, we challenged the M. falcata plants with 30% PEG-6000, and performed physiological and transcriptome analyses. It was found that, the activities of antioxidant enzymes (eg. SOD, POD, and CAT) and soluble sugar content were all increased in the PEG-treated group, as compared to the control group. Transcriptome results showed that a total of 706 genes were differentially expressed in the PEG-treated plants in comparison with the control. Gene enrichment analyses on differentially expressed genes revealed that a number of genes in various pathway were significantly enriched, including the phenylpropanoid biosynthesis (ko00940) and glycolysis/gluconeogenesis (ko00010), indicating the involvement of these key pathways in drought response. Furthermore, the expression levels of seven differentially expressed genes were verified to be involved in drought response in M. falcata by qPCR. Taken together, these results will provide valuable information related to drought response in M. falcata and lay a foundation for molecular studies and genetic breeding of legume crops in future research.

Identification of Quantitative Trait Loci Associated With Iron Deficiency Tolerance in Maize

Iron (Fe) is a limiting factor in crop growth and nutritional quality because of its low solubility. However, the current understanding of how major crops respond to Fe deficiency and the genetic basis remains limited. In the present study, Fe-efficient inbred line Ye478 and Fe-inefficient inbred line Wu312 and their recombinant inbred line (RIL) population were utilized to reveal the physiological and genetic responses of maize to low Fe stress. Compared with the Fe-sufficient conditions (+Fe: 200 μM), Fe-deficient supply (-Fe: 30 μM) significantly reduced shoot and root dry weights, leaf SPAD of Fe-efficient inbred line Ye478 by 31.4, 31.8, and 46.0%, respectively; decreased Fe-inefficient inbred line Wu312 by 72.0, 45.1, and 84.1%, respectively. Under Fe deficiency, compared with the supply of calcium nitrate (N1), supplying ammonium nitrate (N2) significantly increased the shoot and root dry weights of Wu312 by 37.5 and 51.6%, respectively; and enhanced Ye478 by 23.9 and 45.1%, respectively. Compared with N1, N2 resulted in a 70.0% decrease of the root Fe concentration for Wu312 in the -Fe treatment, N2 treatment reduced the root Fe concentration of Ye478 by 55.8% in the -Fe treatment. These findings indicated that, compared with only supplying nitrate nitrogen, combined supply of ammonium nitrogen and nitrate nitrogen not only contributed to better growth in maize but also significantly reduced Fe concentration in roots. In linkage analysis, ten quantitative trait loci (QTLs) associated with Fe deficiency tolerance were detected, explaining 6.2-12.0% of phenotypic variation. Candidate genes considered to be associated with the mechanisms underlying Fe deficiency tolerance were identified within a single locus or QTL co-localization, including ZmYS3, ZmPYE, ZmEIL3, ZmMYB153, ZmILR3 and ZmNAS4, which may form a sophisticated network to regulate the uptake, transport and redistribution of Fe. Furthermore, ZmYS3 was highly induced by Fe deficiency in the roots; ZmPYE and ZmEIL3, which may be involved in Fe homeostasis in strategy I plants, were significantly upregulated in the shoots and roots under low Fe stress; ZmMYB153 was Fe-deficiency inducible in the shoots. Our findings will provide a comprehensive insight into the physiological and genetic basis of Fe deficiency tolerance.