Both deficiency and toxicity of the micronutrient boron lead to severe reductions in crop yield. Despite this agricultural importance, the molecular basis underlying boron homeostasis in plants remains unclear. To identify molecular players involved in boron homeostasis in maize (Zea mays L.), we measured boron levels in the Goodman-Buckler association panel and performed genome-wide association studies. These analyses identified a benzoxazinless (bx) gene, bx3, involved in the biosynthesis of benzoxazinoids, such as DIMBOA, which are major defense compounds in maize. Genes involved in DIMBOA biosynthesis are all located in close proximity in the genome, and benzoxazinoid biosynthesis mutants, including bx3, are all DIMBOA deficient. We determined that leaves of the bx3 mutant have a greater boron concentration than those of B73 control plants, which corresponded with enhanced leaf tip necrosis, a phenotype associated with boron toxicity. By contrast, other DIMBOA-deficient maize mutants did not show altered boron levels or the leaf tip necrosis phenotype, suggesting that boron is not associated with DIMBOA. Instead, our analyses suggest that the accumulation of boron is linked to the benzoxazinoid intermediates indolin-2-one (ION) and 3-hydroxy-ION. Therefore, our results connect boron homeostasis to the benzoxazinoid plant defense pathway through bx3 and specific intermediates, rendering the benzoxazinoid biosynthesis pathway a potential target for crop improvement under inadequate boron conditions.

中文翻译：

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苯并恶嗪类化合物途径与玉米硼稳态的关联


微量营养素硼的缺乏和毒性都会导致作物产量严重下降。尽管在农业上具有重要意义，但植物中硼稳态的分子基础仍不清楚。为了确定参与玉米硼稳态的分子参与者 （Zea mays L.），我们在 Goodman-Buckler 关联面板中测量了硼水平并进行了全基因组关联研究。这些分析确定了一种无苯并恶嗪 （bx） 基因 bx3，该基因参与苯并恶嗪类化合物（如 DIMBOA）的生物合成，这是玉米中的主要防御化合物。参与 DIMBOA 生物合成的基因都位于基因组中非常接近的位置，而苯并恶嗪类生物合成突变体（包括 bx3）都缺乏 DIMBOA。我们确定 bx3 突变体的叶子比 B73 对照植物的叶子具有更高的硼浓度，这与增强的叶尖坏死相对应，这是一种与硼毒性相关的表型。相比之下，其他 DIMBOA 缺陷的玉米突变体没有表现出硼水平或叶尖坏死表型的改变，这表明硼与 DIMBOA 无关。相反，我们的分析表明，硼的积累与苯并恶嗪类中间体吲哚-2-酮 （ION） 和 3-羟基-ION 有关。因此，我们的结果通过 bx3 和特定中间体将硼稳态与苯并恶嗪类植物防御途径联系起来，使苯并恶嗪类生物合成途径成为硼不足条件下作物改良的潜在靶点。