Strigolactone- and Karrikin-Independent SMXL Proteins Are Central Regulators of Phloem Formation.
Strigolactone- and Karrikin-Independent SMXL Proteins Are Central Regulators of Phloem Formation.
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DOI：
10.1016/j.cub.2017.03.014
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发表时间：
2017-04-24
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影响因子：
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通讯作者：
Greb T
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作者：
Wallner ES;López-Salmerón V;Belevich I;Poschet G;Jung I;Grünwald K;Sevilem I;Jokitalo E;Hell R;Helariutta Y;Agustí J;Lebovka I;Greb T
植物干细胞的小生境，即分生组织，需要能量代谢物和信号分子沿韧皮部组织沿着长距离运输。然而，目前还不清楚韧皮部细胞的特化是如何控制的。在这里，我们证明了基因SUPPRESOR OF MAX 2 1-LIKE 3（SMXL 3）、SMXL 4和SMXL 5作为拟南芥韧皮部形成的细胞自主关键调节因子。这三个基因形成SMXL基因家族的未表征的亚支，其介导激素独脚金内酯和karrikin信号传导。独脚金内酯是调节芽和根分枝的内源性信号分子，而外源性karrikin分子在野火后诱导萌发。这两种活性都依赖于F-box蛋白和SCF（Skp，Cullin，F-box）复合物组分MORE AXILLARY GROWTH 2（MAX 2）。独脚金内酯和karrikin感知导致不同SMXL蛋白家族成员的MAX2依赖性降解，这是介导激素效应的关键。然而，SMXL蛋白质降解下游事件的性质以及所有SMXL蛋白质是否介导独脚金内酯或karrikin信号传导尚不清楚。在这项研究中，我们表明，在SMXL基因家族，特别是SMXL 3/4/5缺陷导致强烈的缺陷，韧皮部形成，改变糖的积累，幼苗致死。通过比较蛋白质的稳定性，我们表明，SMXL 3/4/5蛋白质的功能不同的典型独脚金内酯和karrikin信号介质，虽然在功能上可互换与低独脚金内酯/karrikin信号条件下。我们的观察揭示了韧皮部形成的基本机制，并表明SMXL蛋白功能的多样性对于植物分生组织的稳定供能至关重要。SMXL 3/4/5基因作为韧皮部形成的一般启动子SMXL 3/4/5蛋白在韧皮部发育过程中很早就表达并起作用SMXL 3/4/5蛋白不介导独脚金内酯或karrikin信号传导独脚金内酯/karrikin依赖的SMXL蛋白能够取代SMXL 5植物依赖于能量代谢物和信号分子沿着韧皮部组织的长距离运输。Wallner等人表明，韧皮部的形成需要一个与激素信号通路的介质密切相关的蛋白质家族。分析的蛋白质的不依赖于酶的作用对于坚固的韧皮部形成是必不可少的。
Plant stem cell niches, the meristems, require long-distance transport of energy metabolites and signaling molecules along the phloem tissue. However, currently it is unclear how specification of phloem cells is controlled. Here we show that the genes SUPPRESSOR OF MAX2 1-LIKE3 (SMXL3), SMXL4, and SMXL5 act as cell-autonomous key regulators of phloem formation in Arabidopsis thaliana. The three genes form an uncharacterized subclade of the SMXL gene family that mediates hormonal strigolactone and karrikin signaling. Strigolactones are endogenous signaling molecules regulating shoot and root branching whereas exogenous karrikin molecules induce germination after wildfires. Both activities depend on the F-box protein and SCF (Skp, Cullin, F-box) complex component MORE AXILLARY GROWTH2 (MAX2). Strigolactone and karrikin perception leads to MAX2-dependent degradation of distinct SMXL protein family members, which is key for mediating hormonal effects. However, the nature of events immediately downstream of SMXL protein degradation and whether all SMXL proteins mediate strigolactone or karrikin signaling is unknown. In this study we demonstrate that, within the SMXL gene family, specifically SMXL3/4/5 deficiency results in strong defects in phloem formation, altered sugar accumulation, and seedling lethality. By comparing protein stabilities, we show that SMXL3/4/5 proteins function differently to canonical strigolactone and karrikin signaling mediators, although being functionally interchangeable with those under low strigolactone/karrikin signaling conditions. Our observations reveal a fundamental mechanism of phloem formation and indicate that diversity of SMXL protein functions is essential for a steady fuelling of plant meristems. SMXL3/4/5 genes act as general promoters of phloem formation SMXL3/4/5 proteins are expressed and function very early during phloem development SMXL3/4/5 proteins do not mediate strigolactone or karrikin signaling Strigolactone/karrkin-dependent SMXL proteins are able to replace SMXL5 Plants depend on long-distance transport of energy metabolites and signaling molecules along the phloem tissue. Wallner et al. show that phloem formation requires a family of proteins closely related to mediators of a hormonal signalling pathway. An hormone-independent action of the proteins analyzed is essential for robust phloem formation.