Rodriguez-Villalon Antia, Gujas Bojan, van Wijk Ringo, Munnik Teun, Hardtke Christian S
Department of Plant Molecular Biology, University of Lausanne, Biophore Building, Lausanne CH-1015, Switzerland.
Swammerdam Institute for Life Sciences, Section Plant Physiology, University of Amsterdam, Amsterdam 1098 XH, The Netherlands.
Development. 2015 Apr 15;142(8):1437-46. doi: 10.1242/dev.118364. Epub 2015 Mar 26.
Protophloem is a specialized vascular tissue in growing plant organs, such as root meristems. In Arabidopsis mutants with impaired primary root protophloem differentiation, brevis radix (brx) and octopus (ops), meristematic activity and consequently overall root growth are strongly reduced. Second site mutation in the protophloem-specific presumed phosphoinositide 5-phosphatase cotyledon vascular pattern 2 (CVP2), but not in its homolog CVP2-like 1 (CVL1), partially rescues brx defects. Consistent with this finding, CVP2 hyperactivity in a wild-type background recreates a brx phenotype. Paradoxically, however, while cvp2 or cvl1 single mutants display no apparent root defects, the root phenotype of cvp2 cvl1 double mutants is similar to brx or ops, although, as expected, cvp2 cvl1 seedlings contain more phosphatidylinositol-4,5-biphosphate. Thus, tightly balanced phosphatidylinositol-4,5-biphosphate levels appear essential for proper protophloem differentiation. Genetically, OPS acts downstream of phosphatidylinositol-4,5-biphosphate levels, as cvp2 mutation cannot rescue ops defects, whereas increased OPS dose rescues cvp2 cvl1 defects. Finally, all three mutants display higher density and accelerated emergence of lateral roots, which correlates with increased auxin response in the root differentiation zone. This phenotype is also created by application of peptides that suppress protophloem differentiation, clavata3/embryo surrounding region 26 (CLE26) and CLE45. Thus, local changes in the primary root protophloem systemically shape overall root system architecture.
原生韧皮部是生长中的植物器官（如根分生组织）中的一种特殊维管组织。在初级根原生韧皮部分化受损的拟南芥突变体短根（brx）和章鱼（ops）中，分生组织活性以及整体根生长都大幅降低。原生韧皮部特异性假定磷酸肌醇5 - 磷酸酶子叶维管模式2（CVP2）而非其同源物类CVP2 - 1（CVL1）中的第二位点突变部分挽救了brx缺陷。与这一发现一致，在野生型背景下CVP2的过度活跃重现了brx表型。然而，矛盾的是，虽然cvp2或cvl1单突变体没有明显的根缺陷，但cvp2 cvl1双突变体的根表型与brx或ops相似，尽管正如预期的那样，cvp2 cvl1幼苗含有更多的磷脂酰肌醇 - 4,5 - 二磷酸。因此，紧密平衡的磷脂酰肌醇 - 4,5 - 二磷酸水平似乎对原生韧皮部的正常分化至关重要。在遗传学上，OPS作用于磷脂酰肌醇 - 4,5 - 二磷酸水平的下游，因为cvp2突变不能挽救ops缺陷，而增加OPS剂量可挽救cvp2 cvl1缺陷。最后，所有这三个突变体都表现出更高的侧根密度和更快的侧根出现，这与根分化区生长素反应增加相关。这种表型也可通过应用抑制原生韧皮部分化的肽，即clavata3 /胚周围区域26（CLE26）和CLE45来产生。因此，主根原生韧皮部的局部变化会系统性地塑造整个根系结构。
