Root architecture remodelling is critical for forage moisture in water-limited soil. DEEPER ROOTING 1 (DRO1) in Oryza, Arabidopsis, and Prunus has been reported to improve drought avoidance by promoting roots to grow downward and acquire water from deeper soil. In the present study, we found that ZmDRO1 responded more strongly to abscisic acid (ABA)/drought induction in Zea mays ssp. mexicana, an ancestral species of cultivated maize, than in B73. It was proposed that this is one of the reasons why Zea mays ssp. mexicana has a more noticeable change in the downward direction angle of the root and fewer biomass penalties under waterdeficient conditions. Thus, a robust, synthetic ABA/drought-inducible promoter was used to control the expression of ZmDRO1 B73 in Arabidopsis and cultivated maize for drought-resistant breeding. Interestingly, ABA-inducible ZmDRO1 promoted a larger downward root angle and improved grain yield by more than 40% under water-limited conditions. Collectively, these results revealed that different responses to ABA/drought induction of ZmDRO1 confer different drought avoidance abilities, and we demonstrated the application of ZmDRO1 via an ABAinducible strategy to alter the root architecture of modern maize to improve drought adaptation in the field.
SUMMARY Lateral organ boundaries domain (LBD) proteins are plant‐specific transcription factors. Class‐I LBD genes have been widely demonstrated to play pivotal roles in organ development; however, knowledge on class‐II genes remains limited. Here, we report that ZmLBD5, a class‐II LBD gene, is involved in the regulation of maize (Zea mays) growth and the drought response by affecting gibberellin (GA) and abscisic acid (ABA) synthesis. ZmLBD5 is mainly involved in regulation of the TPS‐KS‐GA2ox gene module, which is comprised of key enzyme‐encoding genes involved in GA and ABA biosynthesis. ABA insufficiency increases stomatal density and aperture in overexpression plants and causes a drought‐sensitive phenotype by promoting water transpiration. Increased GA1 levels promotes seedling growth in overexpression plants. Accordingly, CRISPR/Cas9 knockout lbd5 seedlings are dwarf but drought‐tolerant. Moreover, lbd5 has a higher grain yield under drought stress conditions and shows no penalty in well‐watered conditions compared to the wild type. On the whole, ZmLBD5 is a negative regulator of maize drought tolerance, and it is a potentially useful target for drought resistance breeding.
Throughout the history of maize cultivation, ear-related traits have been domesticated. However, little is known about the domesticated genes involved in shaping the ear traits from those of the wild progenitor, teosinte, to those exhibited by modern maize. In this study, five ear traits (kernel row number [KRN], ear length [EL], kernel number per row [KNR], cob diameter [CD], and ear diameter [ED]) were investigated, and eight quantitative trait loci (QTL) hotspots were identified in two maize populations with teosinte gene introgression. We found remarkable enrichment of domesticated and ear-related domesticated genes in qCD1, qCD7, qCD13, qED1, qEL8, qEL10, qKNR11, and qKRN6, suggesting that these eight QTL are domestication hotspots involved in shaping the maize ear from teosinte to modern maize. By combining the QTL identified in this study with the results of the genome-wide association study (GWAS) of ear traits from two association panels, eight candidate domesticated genes related to KRN, KNR, CD, and ED were identified. Considering the expression patterns and sequence variations, Zm00001d025111 and Zm00001d033153, which encode WD40/YVTN and SMAD/FHA proteins, respectively, were proposed as positive regulators of KNR, whereas Zm00001d003083 and Zm00001d005866, which encode isocitrate dehydrogenase and protein disulfide isomerase, respectively, were proposed as negative regulators of KRN. This study presents a frame work for the genomic distribution of ear trait-related and domesticated loci. Several candidate genes with minor effects may be viable targets for further increases in the yield of modern maize.
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