A molecular rheostat adjusts auxin flux to promote root protophloem differentiation
A molecular rheostat adjusts auxin flux to promote root protophloem differentiation
复制标题
DOI：
10.1038/s41586-018-0186-z
复制
发表时间：
2018-06-14
期刊：
影响因子：
64.8
通讯作者：
Hardtke, C. S.
中科院分区：
文献类型：
--
作者：
Marhava, P.;Bassukas, A. E. L.;Hardtke, C. S.
生长素通过几种不同的浓度依赖性效应影响植物发育（1）。在拟南芥根尖中，通过PIN-形成（PIN）蛋白的极性生长素运输产生维持干细胞小生境所需的局部生长素积累（2-4）。在近端，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生长素水平随着细胞分裂而逐渐降低，随后随着细胞分化而逐渐增加（5，6）。然而，分化的时间在细胞档案中是不一致的。例如，发育中的原生韧皮部筛元件（PPSE）在相邻细胞仍然分裂时分化。在这里，我们表明，PPSE分化涉及局部陡峭的后分生生长素梯度。短根（BRX）和与BRX相关的蛋白激酶（PAX）是相互作用的质膜相关的极性定位蛋白，与PIN蛋白共定位于发育中的PPSE的根端。brx和pax突变体均显示PPSE分化受损。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质膜定位依赖于PAX，但生长素负调控BRX质膜结合，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，通过开发PPSE调节生长素通量，从而定时PPSE分化。
Auxin influences plant development through several distinct concentration-dependent effects(1). 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 niche(2-4). 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 differentiate(5,6). 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 plasmamembrane-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.