Preliminary Functional Analysis Of ARLR On Adventitious Root Development In Rice (Oryza Sativa L.)

Seminal root, adventitious roots (also named as crown roots) and lateral roots are main components of fibrous root system of rice, the model plant of cereal crops as well as the most important food crops worldwide. Because the primary root is short-lived, while the adventitious roots grow acropetally along both the main stem and the tillers to keep pace with leaf emergence, the plant’s acquisition of water and nutrients during the growing period is mainly dependent on adventitious and lateral roots. Understanding of the molecular mechanism of development of rice adventitious roots will help us to improve the root architecture of crops using genetic engineering technology.ARL1/CRL1, a key gene for rice adventitious root development has been reported. To investigate the regulating mechanism downstream of ARL1, the transgenic plants with fused gene of ARL1::GR was developed and used for microarray analysis. From the results, we identified the gene ARLR(Adventitious Rootlessl Recovery) as one of the candidates downstream of ARL1.Blast analysis and phylogenetic analysis indicate that the protein coded by ARLR is a member of AGC2 protein kinase subfamily. In this study, we confirmed the result from the microarray analysis by quantitative real time RT-PCR (qRT-PCR). To investigate the function of ARLR, transgenic wild type (WT) and arll mutant plants with overexpression and repression of ARLR were developed. The results indicated that overexpression of ARLR can partially rescue adventitious root development in arll mutant. Knock down the expression of ARLR by RNA interfering (RNAi) in wild type plant, however, did not show significant difference in the adventitious root number compare to the wild type plants. Overexpression of ARLR in wild type plant showed no significant difference in the adventitious root number, but caused a dwarf phenotype. The expression pattern of ARLR was investigated by ARLR promoter driven GUS reporter gene. Histochemical staining for GUS activity in T1 plants showed that ARLR is mainly expressed in the meristematic zone of root tip, the adventitious root primordium, and leaf sheath, while not in leaf and flower. The subcellular localization of ARLR was investigated by transient expression of ARLR fusion with GFP in onion epidermal cells. The results indicated that ARLR is localized in cytoplasm. In vitro Phosphorylation analysis indicated that ARLR protein has kinase activity.Taken together, this study identifies a gene ARLR as a target of ARL1. The data indicate that ARLR is involved in development of adventitious root promordia, while the function of ARLR may be redundant with other genetic factors downstream of ARL1. The present data provide a new insight into the mechanism of adventitious root development in rice under control of ARL1.