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Summary: Tassel branch number (TBN) is a key agronomic trait for adapting to high‐density planting and grain yield in maize. However, the molecular regulatory mechanisms underlying tassel branching are still largely unknown.Here, we used molecular and genetic studies together to show that ZmELF3.1 plays a critical role in regulating TBN in maize.Previous studies showed that ZmELF3.1 forms the evening complex through interacting with ZmELF4 and ZmLUX to regulate flowering in maize and that RA2 and TSH4 (ZmSBP2) suppresses and promotes TBN in maize, respectively. In this study, we show that loss‐of‐function mutants of ZmELF3.1 exhibit a significant increase of TBN. We also show that RA2 directly binds to the promoter of TSH4 and represses its expression, thus leading to reduced TBN. We further demonstrate that ZmELF3.1 directly interacts with both RA2 and ZmELF4.2 to form tri‐protein complexes that further enhance the binding of RA2 to the promoter of TSH4, leading to suppressed TSH4 expression and consequently decreased TBN.Our combined results establish a novel functional link between the ELF3‐ELF4‐RA2 complex and miR156‐SPL regulatory module in regulating tassel branching and provide a valuable target for genetic improvement of tassel branching in maize. [ABSTRACT FROM AUTHOR]

Summary: Flowering time is a key agronomic trait determining environmental adaptation and yield potential of crops. The regulatory mechanisms of flowering in maize still remain rudimentary.In this study, we combine expressional, genetic, and molecular studies to identify two homologous SQUAMOSA PROMOTER BINDING PROTEIN‐LIKE (SPL) transcription factors ZmSPL13 and ZmSPL29 as positive regulators of juvenile‐to‐adult vegetative transition and floral transition in maize.We show that both ZmSPL13 and ZmSPL29 are preferentially expressed in leaf phloem, vegetative and reproductive meristem. We show that vegetative phase change and flowering time are moderately delayed in the Zmspl13 and Zmspl29 single knockout mutants and more significantly delayed in the Zmspl13/29 double mutants. Consistently, the ZmSPL29 overexpression plants display precocious vegetative phase transition and floral transition, thus early flowering. We demonstrate that ZmSPL13 and ZmSPL29 directly upregulate the expression of ZmMIR172C and ZCN8 in the leaf, and of ZMM3 and ZMM4 in the shoot apical meristem, to induce juvenile‐to‐adult vegetative transition and floral transition.These findings establish a consecutive signaling cascade of the maize aging pathway by linking the miR156‐SPL and the miR172‐Gl15 regulatory modules and provide new targets for genetic improvement of flowering time in maize cultivars. [ABSTRACT FROM AUTHOR]

Summary: The epidermal hair and stomata are two types of specialized structures on the surface of plant leaves. On mature maize leaves, stomatal complexes and three types of hairs are distributed in a stereotyped pattern on the adaxial epidermis. However, the spatiotemporal relationship between epidermal hair and stomata development and the regulatory mechanisms governing their formation in maize remain largely unknown.Here, we report that three homologous ZmSPL transcription factors, ZmSPL10, ZmSPL14 and ZmSPL26, act in concert to promote epidermal hair fate on maize leaf. Cytological analyses revealed that Zmspl10/14/26 triple mutants are completely glabrous, but possess ectopic stomatal files. Strikingly, the precursor cells for prickle and bicellular hairs are transdifferentiated into ectopic stomatal complexes in the Zmspl10/14/26 mutants.Molecular analyses demonstrated that ZmSPL10/14/26 bind directly to the promoter of a WUSCHEL‐related homeobox gene, ZmWOX3A, and upregulate its expression in the hair precursor cells. Moreover, several auxin‐related genes are downregulated in the Zmspl10/14/26 triple mutants.Our results suggest that ZmSPL10/14/26 play a key role in promoting epidermal hair fate on maize leaves, possibly through regulating ZmWOX3A and auxin‐related gene expression, and that the fates of epidermal hairs and stomata are switchable. [ABSTRACT FROM AUTHOR]

Keywords: maize; dense planting; lodging resistance; D1; ZmSPL12 EN maize dense planting lodging resistance D1 ZmSPL12 622 624 3 04/11/22 20220401 NES 220401 Introduction of the semi-dwarf genes ( I sd1 i in rice, I RhtB1b i and I RhtD1b i in wheat) has drastically increased lodging resistance and grain yields in these two important crops since the 1960s, resulting in the so called "Green Revolution" (Hedden, 2003). Together, our results demonstrate that I ZmSPL12 i could mimic the function of "Green Revolution" genes to confer reduced plant height and increased lodging resistance, thus facilitating high-density planting and increased yield in maize. [Extracted from the article]

Summary: Maize is a major staple crop widely used for food, feedstocks and industrial products. Shade‐avoidance syndrome (SAS), which is triggered when plants sense competition of light from neighbouring vegetation, is detrimental for maize yield production under high‐density planting conditions. Previous studies have shown that the red and far‐red photoreceptor phytochromes are responsible for perceiving the shading signals and triggering SAS in Arabidopsis; however, their roles in maize are less clear. In this study, we examined the expression patterns of ZmPHYC1 and ZmPHYC2 and found that ZmPHYC1, but not ZmPHYC2, is highly expressed in leaves and is regulated by the circadian clock. Both ZmPHYC1 and ZmPHYC2 proteins are localized to both the nucleus and cytoplasm under light conditions and both of them can interact with themselves or with ZmPHYBs. Heterologous expression of ZmPHYCs can complement the Arabidopsis phyC‐2 mutant under constant red light conditions and confer an attenuated SAS in Arabidopsis in response to shading. Double knockout mutants of ZmPHYC1 and ZmPHYC2 created using the CRISPR/Cas9 technology display a moderate early‐flowering phenotype under long‐day conditions, whereas ZmPHYC2 overexpression plants exhibit a moderately reduced plant height and ear height. Together, these results provided new insight into the function of ZmPHYCs and guidance for breeding high‐density tolerant maize cultivars. [ABSTRACT FROM AUTHOR]

Abstract Crop breeding aims to generate pure inbred lines with multiple desired traits. Doubled haploid (DH) and genome editing using CRISPR/Cas9 are two powerful game-changing technologies in crop breeding. However, both of them still fall short for rapid generation of pure elite lines with integrated favorable traits. Here, we report the development of a Haploid-Inducer Mediated Genome Editing (IMGE) approach, which utilizes a maize haploid inducer line carrying a CRISPR/Cas9 cassette targeting for a desired agronomic trait to pollinate an elite maize inbred line and to generate genome-edited haploids in the elite maize background. Homozygous pure DH lines with the desired trait improvement could be generated within two generations, thus bypassing the lengthy procedure of repeated crossing and backcrossing used in conventional breeding for integrating a desirable trait into elite commercial backgrounds. We report here the development of a novel approach, termed Haploid-Inducer Mediated Genome Editing (IMGE), that combines haploid induction and genome editing technologies to create genome-edited haploids and doubled haploids, so so to accelerate crop breeding. [ABSTRACT FROM AUTHOR]

Maize (Zea mays ssp. mays) is an agronomically important crop and also a classical genetic model for studying the regulation of plant architecture formation, which is a critical determinant of grain yield. Since the 1930s, increasing planting density has been a major contributing factor to the >7-fold increase in maize grain yield per unit land area in the USA, which is accompanied by breeding and utilization of cultivars characterized by high-density-tolerant plant architecture, including decreased ear height, lodging resistance, more upright leaves, reduced tassel branch number, and reduced anthesis–silking interval (ASI). Recent studies demonstrated that phytochrome-mediated red/far-red light signaling pathway and the miR156/SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) regulatory module co-ordinately regulate the shade avoidance response and diverse aspects of plant architecture in responding to shading in Arabidopsis. The maize genome contains 30 ZmSPL genes, and 18 of them are predicted as direct targets of zma-miR156s. Accumulating evidence indicates that ZmSPL genes play important roles in regulating maize flowering time, plant/ear height, tilling, leaf angle, tassel and ear architecture, and grain size and shape. Finally, we discuss ways to exploit maize SPL genes and downstream targets for improving maize plant architecture tailored for high-density planting. [ABSTRACT FROM AUTHOR]

Background and Aims MicroRNAs (miRNAs) play an important role in the responses and adaptation of plants to many stresses including low nitrogen (LN). Characterizing relevant miRNAs will improve our understanding of nitrogen (N) use efficiency and LN tolerance and thus contribute to sustainable maize production. The objective of this study was to identify novel and known miRNAs and their targets involved in the response and adaptation of maize (Zea mays) to LN stress. Methods MiRNAs and their targets were identified by combined analysis of deep sequencing of small RNA and degradome libraries. The identity of target genes was confirmed by gene-specific RNA ligase-mediated rapid amplification of 5′ cDNA ends (RLM-RACE) and by quantitative expression analysis. Key Results Over 150 million raw reads of small RNA and degradome sequence data were generated. A total of 46 unique mature miRNA sequences belonging to 23 maize miRNA families were sequenced. Eighty-five potentially new miRNAs were identified, with corresponding miRNA* also identified for 65 of them. Twenty-five new miRNAs showed >2-fold relative change in response to LN. In addition to known miR169 species, two novel putative miR169 species were identified. Deep sequencing of miRNAs and the degradome, and RLM-RACE and quantitative polymerase chain reaction (PCR) analyses of their targets showed that miRC10- and miRC68-mediated target cleavage may play a major role among miR169 families in the adaptation to LN by maize seedlings. Conclusions Small RNA and degradome sequencing combined with quantitative reverse transcription–PCR and RLM-RACE verification enabled the efficient identification of miRNAs and their target genes. The generated data sets and the two novel miR169 species that were identified will contribute to our understanding of the physiological basis of adaptation to LN stress in maize plants. [ABSTRACT FROM PUBLISHER]