Maize originated from tropical regions and is extremely sensitive to low temperature during germination. Our previous work identified a major QTL, qp1ER1-1, for low temperature germination ability (LTGA) of maize. Here, we introgressed qp1ER1-1 from the tolerant line L220 into the sensitive line PH4CV to generate two near isogenic lines NIL220-3 and NIL220-25. When germinated under cold temperature for 25 days (Cold-25), the NILs showed similar seedling root length and shoot length to L220, but significantly higher than PH4CV. However, when germinated under cold temperature for 15 days (Cold-15) or under normal temperature (25 °C) for 3 days (CK-3), all lines showed similar seedling performance, indicating that introgression of qp1ER1-1 from L220 into PH4CV could improve LTGA of NIL220-3 and NIL220-25. The whole seedlings, including root and shoot, of Cold-15 and CK-3 were harvested for transcriptome analysis, when both stayed at a similar developmental stage. Dry seed embryo was sequenced as a non-germination control (CK-0). Compared with PH4CV, the tolerant line (L220, NIL220-3, and NIL220-25) specifically expressed genes (different expressed genes, DEGs) were identified for CK-0, Cold-15, and CK-3. Then, DEGs identified from Cold-15, but not from CK-0 or CK-3, were defined as tolerant line specifically expressed LTGA genes. Finally, 1786, 174, and 133 DEGs were identified as L220, NIL220-3, and NIL220-25 specifically expressed LTGA genes, respectively. Of them, 27 were common LTGA genes that could be identified from all three tolerant lines, with two (Zm00001d031209 and Zm00001d031292) locating in the confidence interval of qp1ER1-1. In addition, GO analysis revealed that L220 specifically expressed LTGA genes were majorly enriched in the cell division process and plasma membrane related categories. Taken together, these results provided new insight into the molecular mechanism of maize seed LTGA and facilitated the cloning of the qp1ER1-1 gene.
BACKGROUND The correct time for harvesting is a key factor contributing to the production of high‐quality maize seeds. We conducted field experiments to harvest seeds at 11 developmental stages for 3 years, to investigate seed vigor traits in three early maturity maize varieties and two late maturity varieties in one location. RESULTS Significant correlations (r = 0.72 ~ 0.89) were found among six seed‐related traits: standard germination (SG), accelerated aging germination (AAG), cold test germination (CTG), hundred‐seed weight (HSW), seed moisture content (SMC), and ≥ 10 °C accumulated temperature from pollination to harvest (AT10). Analysis of variance showed that harvest stage, year, and variety had significant effects on all traits, and harvest stage displayed the greatest effect. The responses of SG, AAG, CTG, HSW and SMC to harvest stage fitted quadratic models, and AT10 fitted a linear model. From the quadratic models, an ideal harvest time (IHT, the final date to reach maximum SG, AAG, and CTG) could be calculated for each variety. The three early maturity varieties reached their IHT at 54.94–58.44 days after pollination (DAP); the two later maturity varieties reached IHT several days later (at 59.87–59.90 DAP). The early maturity varieties consistently required less AT10 to reach the IHT than the later maturity varieties. However, all of the varieties reached the IHT at similar SMC levels of about 35%. CONCLUSION The later maturity varieties reached the IHT at later DAPs when they acquired more AT10 than the early maturity varieties but both reached it at similar SMC levels. © 2022 Society of Chemical Industry.
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