第1027回生物科学セミナー
Primary root protophloem differentiation requires balance phosphatidylinositol-4,5-biphosphate levels and systemically affects root branchingd
Prof. Christian S. Hardtke（Professor, University of Lausanne）
2015年03月19日(木) 10:30-11:30 理学部 2号館 講堂
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 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, since cvp2 mutation cannot rescue ops defects, whereas increased OPS dosage 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.
