Carbohydrate partitioning from leaves to sink tissues is essential for plant growth and development. The maize (Zea mays) recessive carbohydrate partitioning defective28 (cpd28) and cpd47 mutants exhibit leaf chlorosis and accumulation of starch and soluble sugars. Transport studies with 14C-sucrose (Suc) found drastically decreased export from mature leaves in cpd28 and cpd47 mutants relative to wild-type siblings. Consistent with decreased Suc export, cpd28 mutants exhibited decreased phloem pressure in mature leaves, and altered phloem cell wall ultrastructure in immature and mature leaves. We identified the causative mutations in the Brittle Stalk2-Like3 (Bk2L3) gene, a member of the COBRA family, which is involved in cell wall development across angiosperms. None of the previously characterized COBRA genes are reported to affect carbohydrate export. Consistent with other characterized COBRA members, the BK2L3 protein localized to the plasma membrane, and the mutants condition a dwarf phenotype in dark-grown shoots and primary roots, as well as the loss of anisotropic cell elongation in the root elongation zone. Likewise, both mutants exhibit a significant cellulose deficiency in mature leaves. Therefore, Bk2L3 functions in tissue growth and cell wall development, and this work elucidates a unique connection between cellulose deposition in the phloem and whole-plant carbohydrate partitioning.

中文翻译：

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玉米脆茎 2-Like3，编码 COBRA 蛋白，在细胞壁形成和碳水化合物分配中起作用

从叶子到水槽组织的碳水化合物分配对于植物的生长和发育至关重要。玉米（Zea mays）隐性碳水化合物分配缺陷28（cpd28）和cpd47突变体表现出叶片萎黄和淀粉和可溶性糖的积累。用 14C-蔗糖 (Suc) 进行的转运研究发现，相对于野生型同胞，cpd28 和 cpd47 突变体的成熟叶的输出量急剧下降。与 Suc 输出减少一致，cpd28 突变体在成熟叶片中表现出降低的韧皮部压力，并在未成熟和成熟叶片中改变了韧皮部细胞壁的超微结构。我们确定了脆性茎 2-Like3 (Bk2L3) 基因的致病突变，该基因是 COBRA 家族的成员，参与被子植物的细胞壁发育。据报道，没有任何先前表征的 COBRA 基因会影响碳水化合物的输出。与其他具有特征的 COBRA 成员一致，BK2L3 蛋白定位于质膜，突变体在深色枝条和初生根中形成矮化表型，以及根伸长区各向异性细胞伸长的丧失。同样，两种突变体在成熟叶片中都表现出明显的纤维素缺乏。因此，Bk2L3 在组织生长和细胞壁发育中起作用，这项工作阐明了韧皮部中纤维素沉积与全植物碳水化合物分配之间的独特联系。以及根伸长区各向异性细胞伸长的损失。同样，两种突变体在成熟叶片中都表现出明显的纤维素缺乏。因此，Bk2L3 在组织生长和细胞壁发育中起作用，这项工作阐明了韧皮部中纤维素沉积与全植物碳水化合物分配之间的独特联系。以及根伸长区各向异性细胞伸长的损失。同样，两种突变体在成熟叶片中都表现出明显的纤维素缺乏。因此，Bk2L3 在组织生长和细胞壁发育中起作用，这项工作阐明了韧皮部中纤维素沉积与全植物碳水化合物分配之间的独特联系。