ZmICE1a regulates the defence–storage trade-off in maize endosperm [CUT&Tag]. ZmICE1a regulates the defence–storage trade-off in maize endosperm [CUT&Tag]

The endosperm of cereal grains feeds the entire world as major food supply, however little is known for its defense responses during endosperm development. Inducer of CBF Expression 1 (ICE1) is a known regulator of cold tolerance in plants. ICE1 has a monocot-specific homologue that is preferentially expressed in cereal grains but with an unclear regulatory function. Here, we characterized the function of monocot-specific ZmICE1 (ZmICE1a) in maize (Zea mays) kernel. mRNA in situ hybridization (ISH) revealed that ZmICE1a is predominantly expressed in the peripheral endosperm (AL, SAL, and BETL). Loss-of-function of ZmICE1a reduced starch content and kernel weight. RNA-seq analysis revealed contradicted expression patterns between starch synthesis genes and genes involved in defense and phytohormone synthesis in zmice1a developing endosperm. Coupled with CUT&Tag-seq analysis, we found that ZmICE1a positively regulates genes in starch synthesis, while negatively regulates genes in AL-specific defense and the synthesis of IAA and JA. Explant assays revealed that exogenous IAA or JA induces the expression of numerous defense genes. mRNA ISH assays revealed that the defense genes induced by IAA and JA, exhibit distinct spatial specific expression in BETL and SAL, respectively. Moreover, we dissected a JA-ZmJAZ9-ZmICE1a-MPI signaling axis involved in JA-mediated defense regulation. Overall, our study revealed ZmICE1a as a key regulatory for endosperm defense responses, and coordinates defense-storage tradeoffs during endosperm development. Overall design: Identification of ZmICE1a regulatory functions using RNA-seq and CUT&Tag-seq during maize endosperm development

谷物籽粒的胚乳作为全球主要的食物来源供养着全人类，但目前人们对其在胚乳发育过程中的防御响应机制仍知之甚少。CBF表达诱导因子1（Inducer of CBF Expression 1，ICE1）是已被证实的植物耐寒性调控因子。ICE1存在一个单子叶植物特异性同源基因，该基因在谷物籽粒中偏好性表达，但其调控功能尚不明确。本研究对玉米（Zea mays）籽粒中的单子叶植物特异性ZmICE1（ZmICE1a）的功能进行了鉴定。mRNA原位杂交（mRNA in situ hybridization，ISH）结果显示，ZmICE1a主要在外围胚乳（AL、SAL与BETL）中表达。ZmICE1a功能缺失会降低籽粒的淀粉含量与粒重。RNA测序（RNA-seq）分析显示，在zmice1a突变体的发育胚乳中，淀粉合成基因与防御及植物激素合成相关基因的表达模式呈现显著拮抗现象。结合CUT&Tag测序（CUT&Tag-seq）分析，我们发现ZmICE1a正向调控淀粉合成相关基因的表达，而负向调控糊粉层特异性防御基因以及生长素（Indole-3-acetic acid，IAA）与茉莉酸（Jasmonic acid，JA）的合成基因。外植体实验显示，外源施加的IAA或JA可诱导大量防御基因的表达。mRNA原位杂交实验显示，受IAA与JA诱导的防御基因分别在BETL与SAL中呈现独特的空间表达特异性。此外，我们阐明了一条参与JA介导的防御调控的JA-ZmJAZ9-ZmICE1a-MPI信号轴。综上，本研究证实ZmICE1a是调控胚乳防御响应的关键因子，并在胚乳发育过程中协调防御与储藏物质积累之间的权衡关系。整体实验设计：在玉米胚乳发育过程中，通过RNA-seq与CUT&Tag-seq技术鉴定ZmICE1a的调控功能