Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109, USA.
Plant Physiol. 2013 Jul;162(3):1392-405. doi: 10.1104/pp.113.217174. Epub 2013 May 15.
Adventitious roots emerge from aerial plant tissues, and the induction of these roots is essential for clonal propagation of agriculturally important plant species. This process has received extensive study in horticultural species but much less focus in genetically tractable model species. We have explored the role of auxin transport in this process in Arabidopsis (Arabidopsis thaliana) seedlings in which adventitious root initiation was induced by excising roots from low-light-grown hypocotyls. Inhibition of auxin transport from the shoot apex abolishes adventitious root formation under these conditions. Root excision was accompanied by a rapid increase in radioactive indole-3-acetic acid (IAA) transport and its accumulation in the hypocotyl above the point of excision where adventitious roots emerge. Local increases in auxin-responsive gene expression were also observed above the site of excision using three auxin-responsive reporters. These changes in auxin accumulation preceded cell division events, monitored by a cyclin B1 reporter (pCYCB1;1:GUS), and adventitious root initiation. We examined excision-induced adventitious root formation in auxin influx and efflux mutants, including auxin insensitive1, pin-formed1 (pin1), pin2, pin3, and pin7, with the most profound reductions observed in ATP-binding cassette B19 (ABCB19). An ABCB19 overexpression line forms more adventitious roots than the wild type in intact seedlings. Examination of transcriptional and translational fusions between ABCB19 and green fluorescent protein indicates that excision locally induced the accumulation of ABCB19 transcript and protein that is temporally and spatially linked to local IAA accumulation leading to adventitious root formation. These experiments are consistent with localized synthesis of ABCB19 protein after hypocotyl excision leads to enhanced IAA transport and local IAA accumulation driving adventitious root formation.
不定根从气生植物组织中出现，并且这些根的诱导对于农业上重要植物物种的无性繁殖至关重要。这一过程在园艺物种中得到了广泛研究，但在遗传上可操作的模式物种中关注较少。我们已经在拟南芥（Arabidopsis thaliana）幼苗中探索了生长素运输在这一过程中的作用，其中不定根的起始是通过从低光照下生长的下胚轴中切除根来诱导的。在这些条件下，从茎尖抑制生长素运输会阻止不定根的形成。根切除伴随着放射性吲哚-3-乙酸（IAA）运输的迅速增加及其在切除点上方的下胚轴中的积累，不定根从那里出现。在切除部位上方，使用三个生长素反应报告基因也观察到生长素反应基因表达的局部增加。生长素积累的这些变化先于细胞分裂事件，通过细胞周期蛋白 B1 报告基因（pCYCB1;1:GUS）和不定根起始来监测。我们检查了生长素流入和流出突变体中切除诱导的不定根形成，包括生长素不敏感 1（auxin insensitive1，AUX1）、PIN 形成蛋白 1（pin-formed1，PIN1）、PIN2、PIN3 和 PIN7，其中观察到的最显著减少是在 ABC 转运蛋白 B19（ATP-binding cassette B19，ABCB19）中。ABCB19 过表达系在完整幼苗中比野生型形成更多的不定根。ABCB19 与绿色荧光蛋白之间的转录和翻译融合的检查表明，切除局部诱导了 ABCB19 转录本和蛋白的积累，该积累在时间和空间上与局部 IAA 积累相关，导致不定根形成。这些实验与切除下胚轴后 ABCB19 蛋白的局部合成一致，导致生长素运输增强和局部 IAA 积累，从而驱动不定根形成。
