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1. Dynamic relationships among pathways producing hydrocarbons and fatty acids of maize silk cuticular waxes

   https://doi.org/10.1093/plphys/kiae150  

   Chen, Keting ; Alexander, Liza E ; Mahgoub, Umnia ; Okazaki, Yozo ; Higashi, Yasuhiro ; Perera, Ann M ; Showman, Lucas J ; Loneman, Derek ; Dennison, Tesia S ; Lopez, Miriam ; et al ( March 2024 , Plant Physiology)

   The hydrophobic cuticle is the first line of defense between aerial portions of plants and the external environment. On maize (Zea mays L.) silks, the cuticular cutin matrix is infused with cuticular waxes, consisting of a homologous series of very long-chain fatty acids (VLCFAs), aldehydes, and hydrocarbons. Together with VLC fatty-acyl-CoAs (VLCFA-CoAs), these metabolites serve as precursors, intermediates, and end-products of the cuticular wax biosynthetic pathway. To deconvolute the potentially confounding impacts of the change in silk microenvironment and silk development on this pathway, we profiled cuticular waxes on the silks of the inbreds B73 and Mo17, and their reciprocal hybrids. Multivariate interrogation of these metabolite abundance data demonstrates that VLCFA-CoAs and total free VLCFAs are positively correlated with the cuticular wax metabolome, and this metabolome is primarily affected by changes in the silk microenvironment and plant genotype. Moreover, the genotype effect on the pathway explains the increased accumulation of cuticular hydrocarbons with a concomitant reduction in cuticular VLCFA accumulation on B73 silks, suggesting that the conversion of VLCFA-CoAs to hydrocarbons is more effective in B73 than Mo17. Statistical modeling of the ratios between cuticular hydrocarbons and cuticular VLCFAs reveals a significant role of precursor chain length in determining this ratio. This study establishes the complexity of the product–precursor relationships within the silk cuticular wax-producing network by dissecting both the impact of genotype and the allocation of VLCFA-CoA precursors to different biological processes and demonstrates that longer chain VLCFA-CoAs are preferentially utilized for hydrocarbon biosynthesis.

    

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2. The role of Class Ⅱ KNOX family in controlling compound leaf patterning in Medicago truncatula

   https://doi.org/10.1111/jipb.13549  

   Wang, Xiao ; Zhang, Juanjuan ; Chai, Maofeng ; Han, Lu ; Cao, Xiaohua ; Zhang, Jing ; Kong, Yiming ; Fu, Chunxiang ; Wang, Zeng‐Yu ; Mysore, Kirankumar S. ; et al ( October 2023 , Journal of Integrative Plant Biology)

   Compound leaf development requires the coordination of genetic factors, hormones, and other signals. In this study, we explored the functions of Class ⅡKNOTTED‐like homeobox (KNOXII) genes in the model leguminous plantMedicago truncatula. Phenotypic and genetic analyses suggest thatMtKNOX4,5are able to repress leaflet formation, whileMtKNOX3,9,10are not involved in this developmental process. Further investigations have shown that MtKNOX4 represses the CK signal transduction, which is downstream of MtKNOXⅠ‐mediated CK biosynthesis. Additionally, two boundary genes,FUSED COMPOUND LEAF1(orthologue ofArabidopsisClass MKNOX) andNO APICAL MERISTEM(orthologue ofArabidopsis CUP‐SHAPED COTYLEDON), are necessary for MtKNOX4‐mediated compound leaf formation. These findings suggest, that among the members of MtKNOXⅡ, MtKNOX4 plays a crucial role in integrating the CK pathway and boundary regulators, providing new insights into the roles of MtKNOXⅡ in regulating the elaboration of compound leaves inM. truncatula.

    

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3. Bacterium-enabled transient gene activation by artificial transcription factors for resolving gene regulation in maize

   https://doi.org/10.1093/plcell/koad155  

   Zhao, Mingxia ; Peng, Zhao ; Qin, Yang ; Tamang, Tej Man ; Zhang, Ling ; Tian, Bin ; Chen, Yueying ; Liu, Yan ; Zhang, Junli ; Lin, Guifang ; et al ( May 2023 , The Plant Cell)

   Understanding gene regulatory networks is essential to elucidate developmental processes and environmental responses. Here, we studied regulation of a maize (Zea mays) transcription factor gene using designer transcription activator-like effectors (dTALes), which are synthetic Type III TALes of the bacterial genus Xanthomonas and serve as inducers of disease susceptibility gene transcription in host cells. The maize pathogen Xanthomonas vasicola pv. vasculorum was used to introduce 2 independent dTALes into maize cells to induced expression of the gene glossy3 (gl3), which encodes a MYB transcription factor involved in biosynthesis of cuticular wax. RNA-seq analysis of leaf samples identified, in addition to gl3, 146 genes altered in expression by the 2 dTALes. Nine of the 10 genes known to be involved in cuticular wax biosynthesis were upregulated by at least 1 of the 2 dTALes. A gene previously unknown to be associated with gl3, Zm00001d017418, which encodes aldehyde dehydrogenase, was also expressed in a dTALe-dependent manner. A chemically induced mutant and a CRISPR-Cas9 mutant of Zm00001d017418 both exhibited glossy leaf phenotypes, indicating that Zm00001d017418 is involved in biosynthesis of cuticular waxes. Bacterial protein delivery of dTALes proved to be a straightforward and practical approach for the analysis and discovery of pathway-specific genes in maize.

    

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4. A co-opted steroid synthesis gene, maintained in sorghum but not maize, is associated with a divergence in leaf wax chemistry

   https://doi.org/10.1073/pnas.2022982118  

   Busta, Lucas ; Schmitz, Elizabeth ; Kosma, Dylan K. ; Schnable, James C. ; Cahoon, Edgar B. ( March 2021 , Proceedings of the National Academy of Sciences)

   Virtually all land plants are coated in a cuticle, a waxy polyester that prevents nonstomatal water loss and is important for heat and drought tolerance. Here, we describe a likely genetic basis for a divergence in cuticular wax chemistry between Sorghum bicolor , a drought tolerant crop widely cultivated in hot climates, and its close relative Zea mays (maize). Combining chemical analyses, heterologous expression, and comparative genomics, we reveal that: 1) sorghum and maize leaf waxes are similar at the juvenile stage but, after the juvenile-to-adult transition, sorghum leaf waxes are rich in triterpenoids that are absent from maize; 2) biosynthesis of the majority of sorghum leaf triterpenoids is mediated by a gene that maize and sorghum both inherited from a common ancestor but that is only functionally maintained in sorghum; and 3) sorghum leaf triterpenoids accumulate in a spatial pattern that was previously shown to strengthen the cuticle and decrease water loss at high temperatures. These findings uncover the possibility for resurrection of a cuticular triterpenoid-synthesizing gene in maize that could create a more heat-tolerant water barrier on the plant’s leaf surfaces. They also provide a fundamental understanding of sorghum leaf waxes that will inform efforts to divert surface carbon to intracellular storage for bioenergy and bioproduct innovations. 

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5. The antagonistic MYB paralogs RH1 and RH2 govern anthocyanin leaf markings in Medicago truncatula

   https://doi.org/10.1111/nph.17097  

   Wang, Chongnan ; Ji, Wenkai ; Liu, Yucheng ; Zhou, Peng ; Meng, Yingying ; Zhang, Pengcheng ; Wen, Jiangqi ; Mysore, Kirankumar S. ; Zhai, Jixian ; Young, Nevin D. ; et al ( December 2020 , New Phytologist)

   Patterned leaf coloration in plants generates remarkable diversity in nature, but the underlying mechanisms remain largely unclear.

   Here, usingMedicago truncatulaleaf marking as a model, we show that the classicM. truncatulaleaf anthocyanin spot trait depends on two R2R3 MYB paralogous regulators, RED HEART1 (RH1) and RH2.

   RH1 mainly functions as an anthocyanin biosynthesis activator that specifically determines leaf marking formation depending on its C‐terminal activation motif. RH1 physically interacts with theM. truncatulabHLH protein MtTT8 and the WDR family member MtWD40‐1, and this interaction facilitates RH1 function in leaf anthocyanin marking formation. RH2 has lost transcriptional activation activity, due to a divergent C‐terminal domain, but retains the ability to interact with the same partners, MtTT8 and MtWD40‐1, as RH1, thereby acting as a competitor in the regulatory complex and exerting opposite effects. Moreover, our results demonstrate that RH1 can activate its own expression and that RH2‐mediated competition can repressRH1expression.

   Our findings reveal the molecular mechanism of the antagonistic gene paralogs RH1 and RH2 in determining anthocyanin leaf markings inM. truncatula, providing a multidimensional paralogous–antagonistic regulatory paradigm for fine‐tuning patterned pigmentation.

    

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