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A molecular rheostat adjusts auxin flux to promote root protophloem differentiation
Nature ( IF 64.8 ) Pub Date : 2018-06-01 , DOI: 10.1038/s41586-018-0186-z
P. Marhava , A. E. L. Bassukas , M. Zourelidou , M. Kolb , B. Moret , A. Fastner , W. X. Schulze , P. Cattaneo , U. Z. Hammes , C. Schwechheimer , C. S. Hardtke

Auxin influences plant development through several distinct concentration-dependent effects1. In the Arabidopsis root tip, polar auxin transport by PIN-FORMED (PIN) proteins creates a local auxin accumulation that is required for the maintenance of the stem-cell niche2–4. Proximally, stem-cell daughter cells divide repeatedly before they eventually differentiate. This developmental gradient is accompanied by a gradual decrease in auxin levels as cells divide, and subsequently by a gradual increase as the cells differentiate5,6. However, the timing of differentiation is not uniform across cell files. For instance, developing protophloem sieve elements (PPSEs) differentiate as neighbouring cells still divide. Here we show that PPSE differentiation involves local steepening of the post-meristematic auxin gradient. BREVIS RADIX (BRX) and PROTEIN KINASE ASSOCIATED WITH BRX (PAX) are interacting plasma-membrane-associated, polarly localized proteins that co-localize with PIN proteins at the rootward end of developing PPSEs. Both brx and pax mutants display impaired PPSE differentiation. Similar to other AGC-family kinases, PAX activates PIN-mediated auxin efflux, whereas BRX strongly dampens this stimulation. Efficient BRX plasma-membrane localization depends on PAX, but auxin negatively regulates BRX plasma-membrane association and promotes PAX activity. Thus, our data support a model in which BRX and PAX are elements of a molecular rheostat that modulates auxin flux through developing PPSEs, thereby timing PPSE differentiation.The coordinated action of BREVIS RADIX (BRX) and PROTEIN KINASE ASSOCIATED WITH BRX (PAX) regulates auxin flux during the development of protophloem sieve elements in the root meristem of Arabidopsis.

中文翻译:

分子变阻器调节生长素通量以促进根原韧皮部分化

生长素通过几种不同的浓度依赖性效应影响植物发育。在拟南芥根尖,PIN-FORMED (PIN) 蛋白的极性生长素转运会产生局部生长素积累,这是维持干细胞生态位 2-4 所必需的。最近,干细胞子细胞在最终分化之前反复分裂。这种发育梯度伴随着细胞分裂时生长素水平的逐渐降低,随后随着细胞分化而逐渐增加5,6。然而,细胞文件的分化时间并不统一。例如,当相邻细胞仍在分裂时,开发的原韧皮部筛分元件 (PPSEs) 会发生分化。在这里,我们表明 PPSE 分化涉及分生组织后生长素梯度的局部陡峭化。BREVIS RADIX (BRX) 和与 BRX (PAX) 相关的蛋白激酶是相互作用的质膜相关、极性定位的蛋白质,它们与发育中的 PPSE 根部末端的 PIN 蛋白共定位。brx 和 pax 突变体都显示出受损的 PPSE 分化。与其他 AGC 家族激酶类似,PAX 激活 PIN 介导的生长素流出,而 BRX 强烈抑制这种刺激。有效的 BRX 质膜定位取决于 PAX,但生长素负调节 BRX 质膜结合并促进 PAX 活性。因此,我们的数据支持一个模型,其中 BRX 和 PAX 是分子变阻器的元素,通过发展 PPSE 调节生长素通量,从而计时 PPSE 分化。
更新日期:2018-06-01
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