Gilliland Laura U, Kandasamy Muthugapatti K, Pawloski Lucia C, Meagher Richard B
Department of Genetics, University of Georgia, Athens, Georgia 30602-7223, USA.
Plant Physiol. 2002 Dec;130(4):2199-209. doi: 10.1104/pp.014068.
The ACT2 gene, encoding one of eight actin isovariants in Arabidopsis, is the most strongly expressed actin gene in vegetative tissues. A search was conducted for physical defects in act2-1 mutant plants to account for their reduced fitness compared with wild type in population studies. The act2-1 insertion fully disrupted expression of ACT2 RNA and significantly lowered the level of total actin protein in vegetative organs. The root hairs of the act2-1 mutants were 10% to 70% the length of wild-type root hairs, and they bulged severely at the base. The length of the mutant root hairs and degree of bulging at the base were affected by adjusting the osmolarity and gelling agent of the growth medium. The act2-1 mutant phenotypes were fully rescued by an ACT2 genomic transgene. When the act2-1 mutation was combined with another vegetative actin mutation, act7-1, the resulting double mutant exhibited extensive synergistic phenotypes ranging from developmental lethality to severe dwarfism. Transgenic overexpression of the ACT7 vegetative isovariant and ectopic expression of the ACT1 reproductive actin isovariant also rescued the root hair elongation defects of the act2-1 mutant. These results suggest normal ACT2 gene regulation is essential to proper root hair elongation and that even minor differences may cause root defects. However, differences in the actin protein isovariant are not significant to root hair elongation, in sharp contrast to recent reports on the functional nonequivalency of plant actin isovariants. Impairment of root hair functions such as nutrient mining, water uptake, and physical anchoring are the likely cause of the reduced fitness seen for act2-1 mutants in multigenerational studies.
ACT2基因编码拟南芥中八种肌动蛋白同工型之一,是营养组织中表达最强的肌动蛋白基因。在群体研究中,对act2-1突变体植株的物理缺陷进行了研究,以解释其与野生型相比适应性降低的原因。act2-1插入完全破坏了ACT2 RNA的表达,并显著降低了营养器官中总肌动蛋白的水平。act2-1突变体的根毛长度为野生型根毛的10%至70%,并且在基部严重膨出。通过调整生长培养基的渗透压和胶凝剂,可影响突变体根毛的长度和基部膨出程度。ACT2基因组转基因完全拯救了act2-1突变体的表型。当act2-1突变与另一个营养肌动蛋白突变act7-1结合时,产生的双突变体表现出广泛的协同表型,从发育致死到严重矮化。ACT7营养同工型的转基因过表达和ACT1生殖肌动蛋白同工型的异位表达也拯救了act2-1突变体的根毛伸长缺陷。这些结果表明,正常的ACT2基因调控对于根毛的正常伸长至关重要,即使是微小的差异也可能导致根部缺陷。然而,肌动蛋白同工型的差异对根毛伸长并不显著,这与最近关于植物肌动蛋白同工型功能不等价的报道形成鲜明对比。在多代研究中,act2-1突变体适应性降低可能是由于根毛功能受损,如养分挖掘、水分吸收和物理锚固。