Chen Erwang, Yu Huiqin, He Juan, Peng Di, Zhu Panpan, Pan Shuxing, Wu Xu, Wang Jincang, Ji Chen, Chao Zhenfei, Xu Zhuopin, Wu Yuejin, Chao Daiyin, Wu Yongrui, Zhang Zhiyong
School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei 230027,China.
National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai 200032,China.
Plant Cell. 2023 Oct 30;35(11):4066-4090. doi: 10.1093/plcell/koad215.
Endosperm filling in maize (Zea mays), which involves nutrient uptake and biosynthesis of storage reserves, largely determines grain yield and quality. However, much remains unclear about the synchronization of these processes. Here, we comprehensively investigated the functions of duplicate NAM, ATAF1/2, and CUC2 (NAC)-type transcription factors, namely, ZmNAC128 and ZmNAC130, in endosperm filling. The gene-edited double mutant zmnac128 zmnac130 exhibits a poorly filled kernel phenotype such that the kernels have an inner cavity. RNA sequencing and protein abundance analysis revealed that the expression of many genes involved in the biosynthesis of zein and starch is reduced in the filling endosperm of zmnac128 zmnac130. Further, DNA affinity purification and sequencing combined with chromatin-immunoprecipitation quantitative PCR and promoter transactivation assays demonstrated that ZmNAC128 and ZmNAC130 are direct regulators of 3 (16-, 27-, and 50-kD) γ-zein genes and 6 important starch metabolism genes (Brittle2 [Bt2], pullulanase-type starch debranching enzyme [Zpu1], granule-bound starch synthase 1 [GBSS1], starch synthase 1 [SS1], starch synthase IIa [SSIIa], and sucrose synthase 1 [Sus1]). ZmNAC128 and ZmNAC130 recognize an additional cis-element in the Opaque2 (O2) promoter to regulate its expression. The triple mutant zmnac128 zmnac130 o2 exhibits extremely poor endosperm filling, which results in more than 70% of kernel weight loss. ZmNAC128 and ZmNAC130 regulate the expression of the transporter genes sugars that will eventually be exported transporter 4c (ZmSWEET4c), sucrose and glucose carrier 1 (ZmSUGCAR1), and yellow stripe-like2 (ZmYSL2) and in turn facilitate nutrient uptake, while O2 plays a supporting role. In conclusion, ZmNAC128 and ZmNAC130 cooperate with O2 to facilitate endosperm filling, which involves nutrient uptake in the basal endosperm transfer layer (BETL) and the synthesis of zeins and starch in the starchy endosperm (SE).
玉米（Zea mays）胚乳的充实过程涉及养分吸收和贮藏物质的生物合成，在很大程度上决定了籽粒产量和品质。然而，这些过程的同步性仍有许多尚不清楚。在此，我们全面研究了NAM、ATAF1/2和CUC2（NAC）型重复转录因子ZmNAC128和ZmNAC130在胚乳充实中的功能。基因编辑的双突变体zmnac128 zmnac130表现出籽粒充实不良的表型，籽粒有内腔。RNA测序和蛋白质丰度分析表明，在zmnac128 zmnac130的充实胚乳中，许多参与醇溶蛋白和淀粉生物合成的基因表达降低。此外，DNA亲和纯化测序结合染色质免疫沉淀定量PCR和启动子反式激活分析表明，ZmNAC128和ZmNAC130是3种（16kD、27kD和50kD）γ-醇溶蛋白基因和6种重要淀粉代谢基因（脆性2 [Bt2]、支链淀粉酶型淀粉脱支酶[Zpu1]、颗粒结合淀粉合酶1 [GBSS1]、淀粉合酶1 [SS1]、淀粉合酶IIa [SSIIa]和蔗糖合酶1 [Sus1]）的直接调控因子。ZmNAC128和ZmNAC130在不透明2（O2）启动子中识别一个额外的顺式元件来调控其表达。三突变体zmnac128 zmnac130 o2表现出胚乳充实极差，导致籽粒重量损失超过70%。ZmNAC128和ZmNAC130调控转运蛋白基因最终将输出糖转运蛋白4c（ZmSWEET4c）、蔗糖和葡萄糖载体1（ZmSUGCAR1）以及类黄条纹2（ZmYSL2）的表达，进而促进养分吸收，而O2起辅助作用。总之，ZmNAC128和ZmNAC130与O2协同作用促进胚乳充实，这涉及基部胚乳转移层（BETL）的养分吸收以及粉质胚乳（SE）中醇溶蛋白和淀粉的合成。
