The growth and development of maize roots are closely related to drought tolerance. In order to clarify the molecular mechanisms of drought tolerance between different maize (Zea mays L.) varieties at the protein level, the isobaric tags for relative and absolute quantitation (iTRAQ) quantitative proteomics were used for the comparative analysis of protein expression in the seedling roots of the drought-tolerant Chang 7-2 and drought-sensitive TS141 maize varieties under 20% polyethylene glycol 6000 (PEG 6000)-simulated drought stress. We identified a total of 7723 differentially expressed proteins (DEPs), 1243 were significantly differentially expressed in Chang 7-2 following drought stress, 572 of which were up-regulated and 671 were down-regulated; 419 DEPs were identified in TS141, 172 of which were up-regulated and 247 were down-regulated. In Chang 7-2, the DEPs were associated with ribosome pathway, glycolysis/gluconeogenesis pathway, and amino sugar and nucleotide sugar metabolism. In TS141, the DEPs were associated with metabolic pathway, phenylpropanoid biosynthesis pathway, and starch and sucrose metabolism. Compared with TS141, the higher drought tolerance of Chang 7-2 root system was attributed to a stronger water retention capacity; the synergistic effect of antioxidant enzymes; the strengthen cell wall; the osmotic stabilization of plasma membrane proteins; the effectiveness of recycling amino acid; and an improvement in the degree of lignification. The common mechanisms of the drought stress response between the two varieties included: The promotion of enzymes in the glycolysis/gluconeogenesis pathway; cross-protection against the toxicity of aldehydes and ammonia; maintenance of the cell membrane stability. Based on the proteome sequencing information, the coding region sequences of eight DEP-related genes were analyzed at the mRNA level by quantitative real-time PCR (qRT-PCR). The findings of this study can inform the future breeding of drought-tolerant maize varieties.

Drought is one of the most important factors contributing to crop yield loss. To develop drought‐tolerant maize (Zea mays L.) varieties, it is important to explore the genetic mechanism and genes involved. In this study, we identified 69 quantitative trait loci (QTLs) for plant height, ear height, anthesis‐silking interval, ear weight, cob weight, 100‐kernel weight, and ear length in two F2:3 populations in both drought‐stressed and unstressed conditions. These QTLs explained 4.0 to 17.2% of phenotypic variation in a single watering condition. Approximately 52 of the 69 QTLs were identified under water‐stressed conditions. Moreover, 21 stable QTLs were validated in one or two F2:3 populations under multiple water‐stressed conditions. Remarkably, bin 4.09 (umc2287–umc2011) had two stable QTLs for ear height and anthesis‐silking interval; bin 1.07_1.08 (bnlg1025–mmc0041) identified three stable QTLs for ear, cob, and 100‐kernel weights; bin 4.08_4.09 (umc2041–umc2287) validated four stable QTLs for ear weight, cob weight, 100‐kernel weight, and ear length; and bin 9.04_9.06 (umc1120–umc2134) mapped three stable QTLs for ear weight, cob weight, and ear length that were consistent with phenotypic correlations among traits, supporting pleiotropy of QTLs and playing important roles in conferring growth and yield advantages under drought stress. Additionally, we identified 36 meta‐QTLs across 26 populations under 52 well‐watered and 38 water‐stressed conditions using a meta‐analysis, and we predicted 39 candidate genes in the corresponding meta‐QTL intervals. These results provide valuable information for further mapping quantitative traits and revealing the genetic basis of drought tolerance.

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Major blast resistance (R) genes confer resistance in a gene-for-gene manner. However, little information is available on interactions between R genes. In this study, interactions between two rice blast R genes, Pi-ta and Pi-b, and other minor blast resistance quantitative trait loci (QTLs) were investigated in a recombinant inbred line (RIL) population comprising 243 RILs from a Cybonnet (CYBT) × Saber (SB) cross. CYBT has the R gene Pi-ta and SB has Pi-b. Ten differential isolates of four Magnaporthe oryzae races (IB-1, IB-17, IB-49, and IE-1K) were used to evaluate disease reactions of the 243 RILs under greenhouse conditions. Five resistance QTLs were mapped on chromosomes 2, 3, 8, 9, and 12 with a linkage map of 179 single nucleotide polymorphism markers. Among them, qBR12 (Q1), was mapped at the Pi-ta locus and accounted for 45.41% of phenotypic variation while qBR2 (Q2) was located at the Pi-b locus and accounted for 24.81% of disease reactions. The additive-by-additive epistatic interaction between Q1 (Pi-ta) and Q2 (Pi-b) was detected; they can enhance the disease resistance by an additive 0.93 using the 0 to 9 standard phenotyping method. These results suggest that Pi-ta interacts synergistically with Pi-b.