SummaryHow carbon (sucrose) and nitrogen (amino acid) accumulation is coordinatively controlled in cereal grains remains largely enigmatic. We found that overexpression of the strigolactone (SL) biosynthesis gene CAROTENOID CLEAVAGE DIOXYGENASE 8 (CCD8) resulted in greater ear diameter and enhanced sucrose and amino acid accumulation in maize kernels. Loss of ZmCCD8 function reduced kernel growth with lower sugar and amino acid concentrations. Transcriptomic analysis showed down‐regulation of the transcription factors ZmMYB42 and ZmMYB63 in ZmCCD8 overexpression alleles and up‐regulation in zmccd8 null alleles. Importantly, ZmMYB42 and ZmMYB63 were negatively regulated by the SL signalling component UNBRANCHED 3, and repressed expression of the sucrose transporters ZmSWEET10 and ZmSWEET13c and the lysine/histidine transporter ZmLHT14. Consequently, null alleles of ZmMYB42 or ZmMYB63 promoted accumulation of soluble sugars and free amino acids in maize kernels, whereas ZmLHT14 overexpression enhanced amino acid accumulation in kernels. Moreover, overexpression of the SL receptor DWARF 14B resulted in more sucrose and amino acid accumulation in kernels, down‐regulation of ZmMYB42 and ZmMYB63 expression, and up‐regulation of ZmSWEETs and ZmLHT14 transcription. Together, we uncover a distinct SL signalling pathway that regulates sucrose and amino acid accumulation in kernels. Significant association of two SNPs in the 5′ upstream region of ZmCCD8 with ear and cob diameter implicates its potential in breeding toward higher yield and nitrogen efficiency.

中文翻译：

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ZmCCD8 通过独脚金内酯信号传导调节玉米籽粒中糖和氨基酸的积累


摘要谷物中碳（蔗糖）和氮（氨基酸）积累如何协调控制在很大程度上仍然是个谜。我们发现，独脚金内酯 （SL） 生物合成基因类细粒裂解双加氧酶 8 （CCD8） 的过表达导致玉米粒中玉米穗直径更大，蔗糖和氨基酸积累增强。ZmCCD8 功能的丧失会随着糖和氨基酸浓度的降低而降低籽粒生长。转录组学分析显示 ZmCCD8 过表达等位基因中转录因子 ZmMYB42 和 ZmMYB63 下调，在 zmccd8 无效等位基因中上调。重要的是，ZmMYB42 和 ZmMYB63 受 SL 信号成分 UNBRANCHED 3 的负调控，并抑制蔗糖转运蛋白 ZmSWEET10 和 ZmSWEET13c 以及赖氨酸/组氨酸转运蛋白 ZmLHT14 的表达。因此，ZmMYB42 或 ZmMYB63 的无效等位基因促进了玉米籽粒中可溶性糖和游离氨基酸的积累，而 ZmLHT14 过表达促进了玉米粒中氨基酸的积累。此外，SL 受体 DWARF 14B 的过表达导致籽粒中更多的蔗糖和氨基酸积累，ZmMYB42 和 ZmMYB63 表达下调，ZmSWEETs 和 ZmLHT14 转录上调。我们一起发现了一条独特的 SL 信号通路，该通路可调节籽粒中蔗糖和氨基酸的积累。ZmCCD8 上行 5' 区域的两个 SNP 与穗和玉米棒直径的显著关联表明其在提高产量和氮效率方面的育种潜力。