Vegetative storage proteins (VSPs) are known to serve as nitrogen reserves in many dicot plants but remain undiscovered in grasses, most widely grown group of crops globally. We identified and characterized a VSP in maize and demonstrated that its overexpression improved drought tolerance. Nitrogen supplementation selectively induced a mesophyll lipoxygenase (ZmLOX6), which was targeted to chloroplasts by a novel N-terminal transit peptide of 62 amino acids. When ectopically expressed under the control of various tissue-specific promoters, it accumulated to a fivefold higher level upon expression in the mesophyll cells than the wild-type plants. Constitutive expression or targeted expression specifically to the bundle sheath cells increased its accumulation by less than twofold. The overexpressed ZmLOX6 was remobilized from the leaves like other major proteins during grain development. Evaluated in the field over locations and years, transgenic hybrids overexpressing ZmLOX6 in the mesophyll cells significantly outyielded nontransgenic sibs under managed drought stress imposed at flowering. Additional storage of nitrogen as a VSP in maize leaves ameliorated the effect of drought on grain yield.

中文翻译：

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一种营养储存蛋白可提高玉米的耐旱性

众所周知，营养储存蛋白 (VSP) 在许多双子叶植物中用作氮储备，但在全球种植最广泛的作物组草中仍未发现。我们鉴定并表征了玉米中的 VSP，并证明其过表达提高了耐旱性。氮补充选择性地诱导了一种叶肉脂氧合酶 (ZmLOX6)，该酶通过 62 个氨基酸的新型 N 端转运肽靶向叶绿体。当在各种组织特异性启动子的控制下异位表达时，它在叶肉细胞中的表达水平是野生型植物的五倍。特定于束鞘细胞的组成型表达或靶向表达使其积累增加不到两倍。在谷物发育过程中，过表达的 ZmLOX6 像其他主要蛋白质一样从叶子中重新活化。在不同地点和年份的田间评估中，在开花时施加的可控干旱胁迫下，在叶肉细胞中过度表达 ZmLOX6 的转基因杂种显着超过了非转基因同胞。在玉米叶片中额外储存氮作为 VSP 可改善干旱对谷物产量的影响。