The Function And Molecular Mechanism Of Rice ARL1 Gene In Arabidopsis

Root systems function as a sensor of soil signaling as well as an organ for nutrition and water uptaking.Tap root system,such as root system of Arabidopsis, consists of one primary root and numerous lateral roots.For fibrous root system of most monocot cereal crops,including rice,maize,wheat and barley,adventitious roots are major root component.ARL1 gene has been reported as a transcription factor involved in primordium initiation of adventitious roots in rice,yet its regulation mechanism remains unknown.In this study,we used Arabidopsis,a tap root model plant to investigate the mechanism of ARL1 regulating adventitious roots initiation.Transgenic plants of Arabidopsis with overexpression of ARL1 were used in the research.The results were summerized as followings.1.ARL1 could induce adventitious roots in hypocotyls from pericycle founder cells adjacent to xylem in Arabidopsis.GUS reporter gene driven by ARL1 promoter showed that GUS expression was restricted in vascular bundle,and was inducible by exogenous auxin.ARL1 overexpression transgenic plants showed short and small aerial organs with robust lateral root initiation and primary root elongation in early growth stage.The expression level of some KNOX genes were upregulated in the transgenic plants.Cross section of hypocotyls of overexpression transgenic plants showed that endodermis was missing in hypocotyls.2.ARL1 overexpression transgenic plants grown on medium with cytokinin could form more lateral roots and larger leaves than the wild type(Col-0),but the number of adventitious roots was dominantly reduced.Further studies on cytokinin signaling pathway showed upregulated expressions of AHP1,ARR16 and ARR17 as well as cell cycle-related genes,such as CDKA,CDKB,CYCD,CYCA and CYCB.3.Auxin accumulated in hypocotyls of the transgenic plants.ARL1 overexpression transgenic plants showed insensitivity to NPA treatment in lateral root initiation, while initiation of adventitious roots and primary root elongation were inhibited. Exogenous auxin like NAA,IAA and 2,4-D,did induce adventious roots in the wild type,but the induced adventious roots differed from those in transgenic plants in the initiation position.All these three kinds of auxin treatments significantly inhibited the adventitious rooting on transgenic plant hypocotyls,while the number of adventitious roots recovered under low concertration 2,4-D at 0.005μM and 0.01μM.