Starch synthesis is a key process that influences crop yield and quality, though little is known about the regulation of this complex metabolic pathway. Here, we present the identification of ZmbZIP91 as a candidate regulator of starch synthesis via co-expression analysis in maize (Zea mays L.). ZmbZIP91 was strongly associated with the expression of starch synthesis genes. Reverse tanscription–PCR (RT–PCR) and RNA in situ hybridization indicated that ZmbZIP91 is highly expressed in maize endosperm, with less expression in leaves. Particle bombardment-mediated transient expression in maize endosperm and leaf protoplasts demonstrated that ZmbZIP91 could positively regulate the expression of starch synthesis genes in both leaves and endosperm. Additionally, the Arabidopsis mutant vip1 carried a mutation in a gene (VIP1) that is homologous to ZmbZIP91, displayed altered growth with less starch in leaves, and ZmbZIP91 was able to complement this phenotype, resulting in normal starch synthesis. A yeast one-hybrid experiment and EMSAs showed that ZmbZIP91 could directly bind to ACTCAT elements in the promoters of starch synthesis genes (pAGPS1, pSSI, pSSIIIa, and pISA1). These results demonstrate that ZmbZIP91 acts as a core regulatory factor in starch synthesis by binding to ACTCAT elements in the promoters of starch synthesis genes.

Maize is one of the three major crops worldwide based on its yield and quality. Starch is crucial to both the yield and quality of maize as it accounts more than 60% of the seed weight, and its structure influences the quality of the crop. Starch synthase I (SSI) contributes to the majority of the starch synthase activity in the maize endosperm. An in-depth understanding of the starch synthesis regulatory mechanism would provide opportunities for improving the yield and quality of maize. In this study, ZmPLATZ2, a plant AT-rich sequence and zinc-binding protein (PLATZ) transcription factor related to starch synthesis, was selected based on co-expression analysis. The semiquantitative RT-PCR and qRT-PCR assays revealed that ZmPLATZ2 had a high expression in the endosperm, and reached the peak at 12 days after pollination (DAP). Different treatments demonstrated that ZmPLATZ2 was downregulated by the presence of sucrose. Subsequent transactivation and subcellular localization analyses showed that ZmPLATZ2 was localized in the nuclei without transactivation. Yeast one-hybrid and transient expression in maize endosperm indicated that ZmPLATZ2 could bind to the promoters of ZmSSI, ZmISA1, and ZmISA2 and increase their gene expression. After ZmPLATZ2 overexpression in rice, four starch synthesis genes were significantly upregulated in the transgenic plant, including the OsSSI gene. In vitro DAP-seq data showed that ZmPLATZ2 could bind to the CAAAAAAA element. In conclusion, our data support that ZmPLATZ2 binds to the CAAAAAAA element in the ZmSSI promoter and mediates the Glu signal pathway.

Background: Utilization of heterosis in maize could be critical in maize breeding for boosting grain yield. However, the genetic architecture of heterosis is not fully understood. To dissect the genetic basis of yield-related traits and heterosis in maize, 301 recombinant inbred lines derived from 08 to 641 × YE478 and 298 hybrids from the immortalized F₂(IF₂) population were used to map quantitative trait loci (QTLs) for nine yield-related traits and mid-parent heterosis.Results: We observed 156 QTLs, 28 pairs of loci with epistatic interaction, and 10 significant QTL × environment interactions in the inbred and hybrid mapping populations. The high heterosis in F₁and IF₂populations for kernel weight per ear (KWPE), ear weight per ear (EWPE), and kernel number per row (KNPR) matched the high percentages of QTLs (over 50%) for those traits exhibiting overdominance, whereas a notable predominance of loci with dominance effects (more than 70%) was observed for traits that show low heterosis such as cob weight per ear (CWPE), rate of kernel production (RKP), ear length (EL), ear diameter (ED), cob diameter, and row number (RN). The environmentally stable QTLqRKP3–2was identified across two mapping populations, whileqKWPE9, affecting the trait mean and the mid-parent heterosis (MPH) level, explained over 18% of phenotypic variations. Nine QTLs,qEWPE9–1,qEWPE10–1,qCWPE6,qEL8,qED2–2,qRN10–1,qKWPE9,qKWPE10–1, andqRKP4–3, accounted for over 10% of phenotypic variation. In addition, QTL mapping identified 95 QTLs that were gathered together and integrated into 33 QTL clusters on 10 chromosomes.Conclusions: The results revealed that (1) the inheritance of yield-related traits and MPH in the heterotic pattern improved Reid (PA) × Tem-tropic I (PB) is trait-dependent; (2) a large proportion of loci showed dominance effects, whereas overdominance also contributed to MPH for KNPR, EWPE, and KWPE; (3) marker-assisted selection for markers at genomic regions 1.09–1.11, 2.04, 3.08–3.09, and 10.04–10.05 contributed to hybrid performance per se and heterosis and were repeatedly reported in previous studies using different heterotic patterns is recommended.

Background: Short internodes contribute to plant dwarfism, which is exceedingly beneficial for crop production. However, the underlying mechanisms of internode elongation are complicated and have been not fully understood.Results: Here, we report a maize dwarf mutant,dwarf2014(d2014), which displays shortened lower internodes. Map-based cloning revealed that thed2014gene is a novelbr2allele with a splicing variation, resulting in a higher expression ofBR2-T02instead of normalBR2-T01. Then, we found that the internode elongation ind2014/br2exhibited a pattern of inhibition-normality-inhibition (transient for the ear-internode), correspondingly, at the 6-leaf, 12-leaf and 14-leaf stages. Indeed,BR2encodes a P-glycoprotein1 (PGP1) protein that functions in auxin efflux, and our in situ hybridization assay showed thatBR2was mainly expressed in vascular bundles of the node and internode. Furthermore, significantly higher auxin concentration was detected in the stem apex ofd2014at the 6-leaf stage and strictly in the node region for the ear-internode at the 14-leaf stage. In such context, we propose that BR2/PGP1 transports auxin from node to internode through the vascular bundles, and excessive auxin accumulation in the node (immediately next to the intercalary meristem) region suppresses internode elongation ofd2014.Conclusions: These findings suggest that low auxin levels mediated by BR2/PGP1 in the intercalary meristem region are crucial for internode elongation.