Abstract
Maize ear size and kernel number differ among lines, however, little is known about the molecular basis of ear length and its impact on kernel number. Here, we characterize a quantitative trait locus, qEL7, to identify a maize gene controlling ear length, flower number and fertility. qEL7 encodes 1-aminocyclopropane-1- carboxylate oxidase2 (ACO2), a gene that functions in the final step of ethylene biosynthesis and is expressed in specific domains in developing inflorescences. Confirmation of qEL7 by gene editing of ZmACO2 leads to a reduction in ethylene production in developing ears, and promotes meristem and flower development, resulting in a ~13.4% increase in grain yield per ear in hybrids lines. Our findings suggest that ethylene serves as a key signal in inflorescence development, affecting spikelet number, floral fertility, ear length and kernel number, and also provide a tool to improve grain productivity by optimizing ethylene levels in maize or in other cereals.
Highlights
Maize ear size and kernel number differ among lines, little is known about the molecular basis of ear length and its impact on kernel number
We identified a major QTL, qEL7, for maize ear length and kernel number and developed a set of QTL near-isogenic lines (NILs)21. qEL7Ye478 plants had a significant increase in ear length (EL), kernel number per row (KNR), 100-kernel weight and ear weight (EW), and later flowering, compared with qEL7SL17 (Fig. 1a−g and Supplementary Table 1), they were similar in kernel row number, ear diameter, plant height, leaf length and width (Fig. 1d, e, Supplementary Fig. 1a and Supplementary Table 1)
By careful analysis of developing ears, we found that the floret abortion rate of the florets in the qEL7Ye478 long ear NILs (~18.7%) was dramatically lower than in the qEL7SL17 short ear NILs (~44.7%) (Fig. 1i, l, m, Supplementary Fig. 1c and Supplementary Table 1)
Summary
Maize ear size and kernel number differ among lines, little is known about the molecular basis of ear length and its impact on kernel number. We identified a major QTL, qEL7, for maize ear length and kernel number and developed a set of QTL near-isogenic lines (NILs) (qEL7SL17 and qEL7Ye478)[21]. Like aco2-cr knockout alleles, these promoter-edited alleles showed a significant increase in ear length by 6.1−14.7%, in kernel number per row by 8.6−17.8% and in ear weight by 14.6−24.7%, compared to wild-type siblings (Supplementary Fig. 3m−o and Supplementary Data 5).
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