Drought-resistant Maize Research Articles

Signpost in the maze: high-quality genome of drought-resistant maize germplasm released.

Signpost in the maze: high-quality genome of drought-resistant maize germplasm released.

Genome-wide association study presents insights into the genetic architecture of drought tolerance in maize seedlings under field water-deficit conditions.

Drought stress is one of the most serious abiotic stresses leading to crop yield reduction. Due to the wide range of planting areas, the production of maize is particularly affected by global drought stress. The cultivation of drought-resistant maize varieties can achieve relatively high, stable yield in arid and semi-arid zones and in the erratic rainfall or occasional drought areas. Therefore, to a great degree, the adverse impact of drought on maize yield can be mitigated by developing drought-resistant or -tolerant varieties. However, the efficacy of traditional breeding solely relying on phenotypic selection is not adequate for the need of maize drought-resistant varieties. Revealing the genetic basis enables to guide the genetic improvement of maize drought tolerance. We utilized a maize association panel of 379 inbred lines with tropical, subtropical and temperate backgrounds to analyze the genetic structure of maize drought tolerance at seedling stage. We obtained the high quality 7837 SNPs from DArT's and 91,003 SNPs from GBS, and a resultant combination of 97,862 SNPs of GBS with DArT's. The maize population presented the lower her-itabilities of the seedling emergence rate (ER), seedling plant height (SPH) and grain yield (GY) under field drought conditions. GWAS analysis by MLM and BLINK models with the phenotypic data and 97862 SNPs revealed 15 variants that were significantly independent related to drought-resistant traits at the seedling stage above the threshold of P < 1.02 × 10-5. We found 15 candidate genes for drought resistance at the seedling stage that may involve in (1) metabolism (Zm00001d012176, Zm00001d012101, Zm00001d009488); (2) programmed cell death (Zm00001d053952); (3) transcriptional regulation (Zm00001d037771, Zm00001d053859, Zm00001d031861, Zm00001d038930, Zm00001d049400, Zm00001d045128 and Zm00001d043036); (4) autophagy (Zm00001d028417); and (5) cell growth and development (Zm00001d017495). The most of them in B73 maize line were shown to change the expression pattern in response to drought stress. These results provide useful information for understanding the genetic basis of drought stress tolerance of maize at seedling stage.

Transcription Factor ZmNAC20 Improves Drought Resistance by Promoting Stomatal Closure and Activating Expression of Stress-Responsive Genes in Maize.

Drought is a major environmental threat that limits crop growth, development, and productivity worldwide. Improving drought resistance with genetic engineering methods is necessary to tackle global climate change. It is well known that NAC (NAM, ATAF and CUC) transcription factors play a critical role in coping with drought stress in plants. In this study, we identified an NAC transcription factor ZmNAC20, which regulates drought stress response in maize. ZmNAC20 expression was rapidly upregulated by drought and abscisic acid (ABA). Under drought conditions, the ZmNAC20-overexpressing plants had higher relative water content and survival rate than the wild-type maize inbred B104, suggesting that overexpression of ZmNAC20 improved drought resistance in maize. The detached leaves of ZmNAC20-overexpressing plants lost less water than those of wild-type B104 after dehydration. Overexpression of ZmNAC20 promoted stomatal closure in response to ABA. ZmNAC20 was localized in the nucleus and regulated the expression of many genes involved in drought stress response using RNA-Seq analysis. The study indicated that ZmNAC20 improved drought resistance by promoting stomatal closure and activating the expression of stress-responsible genes in maize. Our findings provide a valuable gene and new clues on improving crop drought resistance.

Genetic variation in ZmSO contributes to ABA response and drought tolerance in maize seedlings

Water scarcity impairs maize growth and yield. Identification and deployment of superior drought-tolerance alleles is desirable for the genetic improvement of stress tolerance in maize. Our previous study revealed that maize sulfite oxidase (SO) catalyzes the oxidation of sulfite to sulfate and may be involved in drought response. But it was unclear whether the natural variation in ZmSO is directly associated with the drought resistance of maize. In the present study, we showed that ZmSO was associated with drought tolerance in maize seedlings, using gene association analysis and a transgene approach. A 14-bp insertion variation, containing two ABA-responsive elements, in the promoter region of ZmSO conferred ABA-inducible expression, leading to increased drought tolerance. Genetic selection of this favorable allele increased drought tolerance. This study has identified elite alleles associated with sulfur metabolism for improving maize drought resistance.

Genome assembly and genetic dissection of a prominent drought-resistant maize germplasm.

In the context of climate change, drought is one of the most limiting factors that influence crop production. Maize, as a major crop, is highly vulnerable to water deficit, which causes significant yield loss. Thus, identification and utilization of drought-resistant germplasm are crucial for the genetic improvement of the trait. Here we report on a high-quality genome assembly of a prominent drought-resistant genotype, CIMBL55. Genomic and genetic variation analyses revealed that 65 favorable alleles of 108 previously identified drought-resistant candidate genes were found in CIMBL55, which may constitute the genetic basis for its excellent drought resistance. Notably, ZmRtn16, encoding a reticulon-like protein, was found to contribute to drought resistance by facilitating the vacuole H+-ATPase activity, which highlights the role of vacuole proton pumps in maize drought resistance. The assembled CIMBL55 genome provided a basis for genetic dissection and improvement of plant drought resistance, in support of global food security.

Perl scripts used in "Genome assembly and genetic dissection of a prominent drought-resistant maize germplasm"

Perl scripts used in "Genome assembly and genetic dissection of a prominent drought-resistant maize germplasm"

Effect of rainfall and temperature variability on maize yield in the Asante Akim North District, Ghana

One of the largest consumed and grown cereals in Ghana is maize. However, there is a dearth of research on the response of maize yield to rainfall and temperature variability in Ghana. Precisely, prior studies conducted in Ghana have employed only quantitative approaches to explore the effect of climate variability on the yield of food crops including maize. However, this study combined both quantitative and qualitative approaches to investigate the effect of rainfall and temperature variability on maize yield in the Asante Akim North District of the Ashanti Region, Ghana. Since research will help the decision-making process of the policymakers at several cadres of managerial leadership of the United Nations Sustainable Development Goals (SDGs) all around the world where the goals are intended, this study will have significant implications on the attainment of the SDGs particularly Goals 1 (no poverty), 2 (zero hunger), and 13 (climate action). Pragmatic research philosophy was utilized with the aid of questionnaire surveys involving 150 maize farmers and three focus group discussions in three purposively chosen communities (Ananekrom, Juansa, and Agogo). The Mann-Kendall trend test was used to evaluate the trends of rainfall, temperature, and maize yield data for the period 2012 to 2021 in the study district. Multiple regression was used to assess the effect of rainfall and temperature variability on maize yield. Results showed that the surveyed maize farmers perceived rising temperatures and erratic rainfall patterns. Similarly, the Mann-Kendall trend test results revealed a significant temperature rise (p < 0.05) and an increasing rainfall pattern (p > 0.05). The increasing annual rainfall and rising temperature trends increased maize yield significantly (p < 0.05) in the district from 2012 to 2021 contributing about 70% of the yield variation. The surveyed maize farmers implemented key on-farm and off-farm practices including planting drought-resistant maize varieties, crop rotation, changing diets, and selling assets to adapt to the rainfall and temperature variability. The increasing annual rainfall and temperature patterns significantly affect maize yield positively in the Asante Akim North district stressing the need for continued implementation of adaptation practices such as planting high-yielding and drought-resistant maize varieties to enhance household food security. Furthermore, the results demonstrate the urgent need for policy formulation by policymakers to make maize production resilient to the adverse impacts of the changing rainfall and rising temperature trends in Ghana.

Comparative Gene Enrichment Analysis for Drought Tolerance in Contrasting Maize Genotype.

Drought stress is a significant abiotic factor influencing maize growth and development. Understanding the molecular mechanism of drought tolerance is critical to develop the drought tolerant genotype. The identification of the stress responsive gene is the first step to developing a drought tolerant genotype. The aim of the current research was to pinpoint the genes that are essential for conserved samples in maize drought tolerance. In the current study, inbred lines of maize, 478 and H21, a drought-tolerant and susceptible line, were cultivated in the field and various treatments were applied. The circumstances during the vegetative stage (severe drought, moderate drought and well-watered environments) and RNA sequencing were used to look into their origins. In 478, 68%, 48% and 32% of drought-responsive genes (DRGs) were found, with 63% of DRGs in moderate drought and severe drought conditions in H21, respectively. Gene ontology (GO) keywords were explicitly enriched in the DRGs of H21, which were considerably over-represented in the two lines. According to the results of the GSEA, "phenylpropanoid biosynthesis" was exclusively enriched in H21, but "starch and sucrose metabolism" and "plant hormone signal transduction" were enhanced in both of the two lines. Further investigation found that the various expression patterns of genes linked to the trehalose biosynthesis pathway, reactive oxygen scavenging, and transcription factors, may have a role in maize's ability to withstand drought. Our findings illuminate the molecular ways that respond to lack and offer gene resources for maize drought resistance. Similarly, SNP and correlation analysis gave us noticeable results that urged us to do the same kind of analysis on other crops. Additionally, we isolated particular transcription factors that could control the expression of genes associated to photosynthesis and leaf senescence. According to our findings, a key factor in tolerance is the equilibrium between the induction of leaf senescence and the preservation of photosynthesis under drought.

Co-Expression of ZmVPP1 with ZmNAC111 Confers Robust Drought Resistance in Maize.

Drought is a primary environmental factor limiting maize production globally. Although transferring a single gene to maize can enhance drought resistance, maize response to water deficit requires further improvement to accommodate the steadily intensifying drought events worldwide. Here, we generated dual transgene lines simultaneously overexpressing two drought-resistant genes, ZmVPP1 (encoding a vacuolar-type H+ pyrophosphatase) and ZmNAC111 (encoding a NAM, ATAF, and CUC (NAC)-type transcription factor). Following drought stress, survival rates of the pyramided transgenic seedlings reached 62-66%, while wild-type and single transgene seedling survival rates were 23% and 37-42%, respectively. Maize seedlings co-expressing ZmVPP1 and ZmNAC111 exhibited higher photosynthesis rates, antioxidant enzyme activities, and root-shoot ratios than the wild type, and anthesis-silking intervals were shorter while grain yields were higher under water deficit conditions in field trials. Additionally, RNA-sequencing analysis confirmed that photosynthesis and stress-related metabolic processes were stimulated in the dual transgene plants under drought conditions. The findings in this work illustrate how high co-expression of different drought-related genes can reinforce drought resistance over that of individual transgene lines, providing a path for developing arid climate-adapted elite maize varieties.

Elevated CO2 enhanced water use efficiency of wheat to progressive drought stress but not on maize.

Global rising atmospheric CO2 concentration ([CO2]) and drought stress exert profound influences on crop growth and yield. The objective of the present study was to investigate the responses of leaf gas exchange and plant water use efficiency (WUE) of wheat (C3) and maize (C4) plants to progressive drought stress under ambient (a[CO2], 400 ppm) and elevated (e[CO2], 800 ppm) atmospheric CO2 concentrations. The fraction of transpirable soil water (FTSW) was used to evaluate soil water status in the pots. Under non-drought stress, e[CO2] increased the net photosynthetic rate (An) solely in wheat, and dry matter accumulation (DMA), whereas it decreased stomatal conductance (g s) and water consumption (WC), resulting in enhanced WUE by 27.82% for maize and 49.86% for wheat. After onset of progressive soil drying, maize plants in e[CO2] showed lower FTSW thresholds than wheat, at which e.g. gs (0.31 vs 0.40) and leaf relative water content (0.21 vs 0.43) starts to decrease, indicating e[CO2] conferred a greater drought resistance in maize. Under the combination of e[CO2] and drought stress, enhanced WUE was solely found in wheat, which is mainly associated with increased DMA and unaffected WC. These varied responses of leaf gas exchange and WUE between the two species to combined drought and e[CO2] suggest that specific water management strategies should be developed to optimize crop WUE for different species in a future drier and CO2-enriched environment.

Anti-gravity stem-seeking restoration algorithm for maize seed root image phenotype detection

Root phenotype detection is key to cultivating seeds with excellent traits, and requires a complete root image. However, soil occlusion, uneven lighting, and other factors cause broken points and segments in the root image. To solve this problem, an anti-gravity stem-seeking (AGSS) root image restoration algorithm is proposed in this paper to repair root images and extract root phenotype information for different resistant maize seeds. First, the obtained root image was processed using uniform illumination, grayscale, binarization, and morphological filtering to separate it from the background. Subsequently, a root skeleton map was generated using a thinning algorithm for pixel-level image processing, and the Taproot junction G was obtained. Subsequently, root pixel coordinates were obtained by traversing the root skeleton map.All root-segment endpoint coordinates were obtained using the endpoint judgment rule and stored in the endpoint list.The lateral and primary root endpoints were separated based on the lateral root judgment rule, and stored in the side root and primary root endpoint lists, respectively. Subsequently, the primary root endpoints were processed and fitted in the order short to long using arbitrary-two-endpoint spacing until all breakpoints of the primary root were found.The coordinates of the top endpoints of each principal root were obtained. Finally, the top endpoint was connected to point G based on the Bezier curve-fitting method to achieve complete root repair. The proposed AGSS root image restoration algorithm was applied to detect the root systems of maize with different resistances and wheat to evaluate its performance against the standard dataset.The results indicated a detection accuracy of greater than 90% for root taproot length and diameter.It was also found that maize drought resistance was positively correlated with root length and diameter, but negatively with the lateral root number.In contrast, the waterlogging and salt resistance traits of maize were positively correlated with the number of lateral roots. In conclusion, the proposed AGSS root image restoration algorithm can quickly and effectively repair root images, is suitable for different resistance evaluations of maize seeds, and is conducive to the detection of root phenotypes. Compared with deep learning methods, this algorithm displays advantages of fast repair, low hardware platform requirements, and less requirement of training images. The algorithm is highly suitable for deploying in small embedded systems, with broad application prospects.

Exogenous silicon alleviates drought stress in maize by improving growth, photosynthetic and antioxidant metabolism

Extreme dry weather caused by global climate change will reduce the growth and yield of plant crops. Silicon (Si) can improve plant growth and the resistance to various stresses. However, its effects on maize drought stress of the jointing and tasseling stages are unclear in the field. Therefore, the present study was carried out to investigate the effect of growth, photosynthetic and antioxidant metabolism on maize under moderate and severe drought stress with or without Si application (5, 15, 25 g·L−1) in the large farmland moisture control test field. Drought stress down-regulated plant height growth rate (25.80% ~ 39.11%), shoot dry weight (40.42%~68.97%), root dry weight (31.34% ~ 57.96%) and yield (14.51% ~ 36.52%) in the both stages, respectively. With the increase of drought stress, actual photochemical efficiency of PSⅡ (ΦPSⅡ), maximum photochemical efficiency of PSⅡ (Fv/Fm) and photochemical quenching (qP) decreased at different degrees while the non-photochemical quenching (NPQ) increased. One-to-twofold increase was observed in the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) in the drought-stressed conditions. Exogenous Si alleviated drought stress to a certain extent of damage, enhanced plant growth, photosynthetic pigment contents, chlorophyll fluorescence parameters, gas exchange parameters, photosynthetic enzymes activity, the stomatal size and stomatal aperture, inhibited the increase in the superoxide free radical ion (O2·−) production rate, hydrogen peroxide (H2O2), malondialdehyde (MDA) and electrolyte leakage (EL), and further increased the key antioxidant enzymes activities and the osmotic regulatory substance contents. The activities of monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), and the contents of ascorbate (AsA) and glutathione (GSH) increased, and the contents of dehydroascorbate (DHA) and oxidized glutathione (GSSG) declined by Si application in both stages. Therefore, exogenous Si could decrease maize oxidative stress response in drought-stressed by strengthening the antioxidant defense system and photosynthetic metabolism, improving the AsA-GSH cycle, increasing osmotic substance contents, as well as playing a vital role in improving the drought resistance of maize. Overall, the external use of Si ameliorated growth, photosynthetic and antioxidant metabolism under drought stress.

Natural variations of ZmSRO1d modulate the trade-off between drought resistance and yield by affecting ZmRBOHC-mediated stomatal ROS production in maize

While crop yields have historically increased, drought resistance has become a major concern in the context of global climate change. The trade-off between crop yield and drought resistance is a common phenomenon; however, the underlying molecular modulators remain undetermined. Through genome-wide association study, we revealed that three non-synonymous variants in a drought-resistant allele of ZmSRO1d-R resulted in plasma membrane localization and enhanced mono-ADP-ribosyltransferase activity of ZmSRO1d toward ZmRBOHC, which increased reactive oxygen species (ROS) levels in guard cells and promoted stomatal closure. ZmSRO1d-R enhanced plant drought resilience and protected grain yields under drought conditions, but it led to yield drag under favorable conditions. In contrast, loss-of-function mutants of ZmRBOHC showed remarkably increased yields under well-watered conditions, whereas they showed compromised drought resistance. Interestingly, by analyzing 189 teosinte accessions, we found that the ZmSRO1d-R allele was present in teosinte but was selected against during maize domestication and modern breeding. Collectively, our work suggests that the allele frequency reduction of ZmSRO1d-R in breeding programs may have compromised maize drought resistance while increased yields. Therefore, introduction of the ZmSRO1d-R allele into modern maize cultivars would contribute to food security under drought stress caused by global climate change.

Increase in root density induced by coronatine improves maize drought resistance in North China

Drought stress caused by insufficient irrigation or precipitation impairs agricultural production worldwide. In this study, a two-year field experiment was conducted to investigate the effect of coronatine (COR), a functional analog of jasmonic acid (JA), on maize drought resistance. The experiment included two water treatments (rainfed and irrigation), four COR concentrations (mock, 0 μmol L−1; A1, 0.1 μmol L−1; A2, 1 μmol L−1; A3, 10 μmol L−1) and two maize genotypes (Fumin 985 (FM985), a drought-resistant cultivar and Xianyu 335 (XY335), a drought-sensitive cultivar). Spraying 1 μmol L−1 COR at seedling stage increased surface root density and size, including root dry matter by 12.6%, projected root area by 19.0%, average root density by 51.9%, and thus root bleeding sap by 28.2% under drought conditions. COR application also increased leaf area and SPAD values, a result attributed to improvement of the root system and increases in abscisic acid (ABA), JA, and salicylic acid (SA) contents. The improvement of leaves and roots laid the foundation for increasing plant height and dry matter accumulation. COR application reduced anthesis and silking interval, increasing kernel number per ear. COR treatment at 1 μmol L−1 increased the yield of XY335 and FM985 by 7.9% and 11.0%, respectively. Correlation and path analysis showed that grain yields were correlated with root dry weight and projected root area, increasing maize drought resistance mainly via leaf area index and dry matter accumulation. Overall, COR increased maize drought resistance mainly by increasing root dry weight and root area, with 1 μmol L−1 COR as an optimal concentration.

Characterizing and designing promoter of gene \(\textit{ZmDREB2.7}\) into plant expression vector

In the regulation of gene expression, particularly abiotic-stress tolerance characteristics in plants, inducible promoters play an essential role in ensuring the endurance and productivity of crops. In several previous studies, the ZmDREB2.7 gene and some DNA polymorphisms in its promoter have been shown to enhance drought tolerance traits in maize (Zea mays L.). With the goal of creating a strong drought-tolerant promoter region derived from maize, in this study, the 1 kilobase 5’-upstream region of the ZmDREB2.7 coding sequence from the drought resistant maize line Tevang1 was isolated and characterized. Essential putative cis-regulatory elements (as TATA box or CAAT box) and other elements that regulate drought tolerant properties (as RY/G box, ABRE element or MYB core) were investigated. After that, we designed the transgenic plant vector containing the isolated promoter and the ZmDREB2.7 gene which were isolated in our earlier study. The promoter segment was removed 20 nucleotides ahead of the transcription start site and transferred into the recombinant pZY vector containing the ZmDREB2.7 gene. In conclusion, we created a recombinant vector containing the modified ZmDREB2.7 promoter and the ZmDREB2.7 gene segment derived from maize. This is a promising resource for the creation of a transgenic cultivar with effective resistance to dry stress in the future. Besides, we will keep on examining other potential genetic regions and promoters to diversify sources of genetic materials as well as understand deeper the stress-resistant transgenic plants.

A Genome-Wide Association Study Dissects the Genetic Architecture of the Metaxylem Vessel Number in Maize Brace Roots.

Metaxylem vessels in maize brace roots are key tissue, and their number (MVN) affects plant water and inorganic salt transportation and lodging resistance. Dissecting the genetic basis of MVN in maize brace roots can help guide the genetic improvement of maize drought resistance and lodging resistance during late developmental stages. In this study, we used 508 inbred lines with tropical, subtropical, and temperate backgrounds to analyze the genetic architecture of MVN in maize brace roots. The phenotypic variation in MVN in brace roots was evaluated in three environments, which revealed broad natural variation and relative low levels of heritability (h2 = 0.42). Stiff-stalk lines with a temperate background tended to have higher MVNs than plants in other genetic backgrounds. MVN was significantly positively correlated with plant height, tassel maximum axis length, ear length, and kernel number per row, which indicates that MVN may affect plant morphological development and yield. In addition, MVN was extremely significantly negatively correlated with brace root radius, but significantly positively correlated with brace root angle (BRA), diameter, and number, thus suggesting that the morphological function of some brace root traits may be essentially determined by MVN. Association analysis of MVN in brace roots combined 1,253,814 single nucleotide polymorphisms (SNPs) using FarmCPU revealed a total of nine SNPs significantly associated with MVN at P < 7.96 × 10–7. Five candidate genes for MVN that may participate in secondary wall formation (GRMZM2G168365, GRMZM2G470499, and GRMZM2G028982) and regulate flowering time (GRMZM2G381691 and GRMZM2G449165). These results provide useful information for understanding the genetic basis of MVN in brace root development. Further functional studies of identified candidate genes should help elucidate the molecular pathways that regulate MVN in maize brace roots.

Identification and expression analysis revealed drought stress-responsive Calmodulin and Calmodulin-like genes in maize

ABSTRACT Calmodulin (CaM) and Calmodulin-like (CML) genes are the primary families of Calcium (Ca2+) sensors which are found to be involved in response to various stresses. Some genes involved in Ca2+ signal transduction have been genome-wide characterized in various species. However, the detailed identification, characterization, and expression profilings of ZmCaM and ZmCML genes in maize remain poorly understood, especially in the response to drought stress. In this study, a total of 7 ZmCaMs and 46 ZmCMLs are identified in maize and unevenly located on 10 chromosomes. ZmCaM and ZmCML proteins are divided into 9 groups. Protein structures analysis shows that the EF-hand motif number of ZmCaMs/ZmCMLs ranges from 3 to 4 and 2 to 4, respectively. A large number of cis-regulatory elements are found in the promoter regions of ZmCaM and ZmCML genes. ZmCaM and ZmCML genes display highly diversified tissue-specific expression patterns. Furthermore, ZmCaM2, ZmCML3, ZmCML6, ZmCML8, ZmCML19, ZmCML24, ZmCML27, ZmCML28, ZmCML36, ZmCML39, and ZmCML40 are induced significantly under drought stress through RNA-seq data and RT-qPCR. Taken together, these results will help to understand the critical roles of ZmCaM and ZmCML genes played in drought resistance and provide valuable candidate genes that could be used to develop drought-resistant maize.

Physiological Mechanism of Exogenous Silicon Alleviating Drought Stress in Maize

With the global warming, the impact of drought on agricultural production is increasingly prominent. Maize has a long growth period, high water demand, and is more sensitive to drought. Therefore, drought has always been one of the limited factors affecting the stable and increased on global maize production. Si promotes seed germination and seedling growth, enhances agricultural sustainability. However, its effects on different growth stages and different drought degree of maize are unclear in the field. In this experiment, to study its effects of drought in the large farmland moisture control test field (Xianyu 335) combined with exogenous Si during growth and development in maize. Exposed to drought-stressed conditions, Si further aggrandized antioxidant enzyme activities, reduced ROS contents, not only moderated AsA/DHA ratio but also GSH/GSSG ratio. Adding exogenous Si, the plant height growth rate, biomass, photosynthetic pigment contents, gas exchange parameters, photosynthetic enzymes activity, the stomatal size and aperture improved significantly, the contents of osmolyte further increased, as well as the increases were greater in the jointing stage than in the tasseling stage. In summary, applying exogenous Si can enhance the photosynthesis capacity of plants, promote the synthesis of osmotic substances, thus improving plant water metabolism balance, and enhance the antioxidant system, remove toxic substances, reduce membrane peroxidation, maintain cell membrane stability, alleviate stomatal limitation, and enhance maize drought resistance of the plant, thereby increasing yield.

Poly-\u03b3-glutamic acid enhanced the drought resistance of maize by improving photosynthesis and affecting the rhizosphere microbial community

BackgroundCompared with other abiotic stresses, drought stress causes serious crop yield reductions. Poly-γ-glutamic acid (γ-PGA), as an environmentally friendly biomacromolecule, plays an important role in plant growth and regulation.ResultsIn this project, the effect of exogenous application of γ-PGA on drought tolerance of maize (Zea mays. L) and its mechanism were studied. Drought dramatically inhibited the growth and development of maize, but the exogenous application of γ-PGA significantly increased the dry weight of maize, the contents of ABA, soluble sugar, proline, and chlorophyll, and the photosynthetic rate under severe drought stress. RNA-seq data showed that γ-PGA may enhance drought resistance in maize by affecting the expression of ABA biosynthesis, signal transduction, and photosynthesis-related genes and other stress-responsive genes, which was also confirmed by RT–PCR and promoter motif analysis. In addition, diversity and structure analysis of the rhizosphere soil bacterial community demonstrated that γ-PGA enriched plant growth promoting bacteria such as Actinobacteria, Chloroflexi, Firmicutes, Alphaproteobacteria and Deltaproteobacteria. Moreover, γ-PGA significantly improved root development, urease activity and the ABA contents of maize rhizospheric soil under drought stress. This study emphasized the possibility of using γ-PGA to improve crop drought resistance and the soil environment under drought conditions and revealed its preliminary mechanism.ConclusionsExogenous application of poly-γ-glutamic acid could significantly enhance the drought resistance of maize by improving photosynthesis, and root development and affecting the rhizosphere microbial community.

Evaluation of Drought Tolerance in Maize Inbred Lines Selected from the Shaan A Group and Shaan B Group

Drought is one of the most prevailing abiotic stresses affecting the growth, development, and productivity of maize. Knowledge of drought tolerance could help in maize improvement. However, less research has been done to comprehensively evaluate the drought tolerance of maize inbred lines. We used 27 elite maize inbred lines selected from Shaan A group and Shaan B group breeding populations to estimate their drought tolerance in 3 years 2 locations under normal field conditions and low irrigation. Using principal component analysis (PCA) and GGE biplots, all inbred lines, including the controls, could be divided into four types. Ten lines could be categorized as the high-yield drought-resistant type (‘KB081’, ‘KA105’, ‘KB417’, ‘KB215’, ‘KB-7’, ‘2013KB-37’, ‘KA203’, ‘2012KA-34’, ‘KA225’, and ‘91227’) because of their stability and wide adaptability. Compared with the controls, a large proportion of the inbred lines selected from Shaan A and Shaan B breeding populations demonstrated higher drought resistance. Our results suggest that multi-year drought screening can be used as a tool to improve the drought resistance of maize inbred lines and provide a scientific basis for making better use of the Shaan A and Shaan B maize inbred lines to breed new varieties and to identify existing drought-resistant maize varieties.