Phenotypic characterization of rice WOX10 gene in Arabidopsis thaliana hypocotyls root formation

Abstract

Plants are sessile living organisms that remain attached to the soil for their nutrition and survival. Different environmental and other stress conditions such as plant diseases lead to several adaptations to withstand them. The cross-talk between various transcription factors and signalling hormones is crucial for overall plant growth and development. Hence it is essential to study the role and action of these transcription factors involved in hormonal signalling. Plants obtain their food and nutrition through leaves and roots, respectively. Leaves form the upper part, and roots form the lower part hidden in the ground; sometimes roots are seen emerging from the upper parts of plants, termed adventitious roots (AR). For example, crown roots (CR) in rice and lateral roots in Arabidopsis, these develop from non-root tissues and play a vital role in root system architecture. Root system architecture and origin of adventitious roots have diverged across the plant kingdom. In Arabidopsis, both adventitious and lateral roots originate from the xylem-pole of hypocotyl and primary root. In contrast, in rice, adventitious develop from the innermost tissues of the shoot. But the mechanism controlling these initiations and subsequent growth is underexplored.(Bellini et al., 2014; Itoh et al., 2005; Rebouillat et al., 2009) Recently the Spatial-temporal expression studies of rice PLETHORA (OsPLT) and WUSCHEL RELATED HOMEOBOX 10 (OsWOX10) genes showed an essential role in the adventitious root formation (Garg et al., 2020).In this thesis, we suggested overexpressing the rice OsWOX10 gene in the Arabidopsis wild type andmutant lines, hoping to observe and show that OsWOX10 is involved in adventitious root formation, and the function of the WOX family is conserved across the plant species (monocot and dicots). The next objective was to analyze whether the overexpression of OsWOX10 is enough to rescue and initiate the process of adventitious root development in the Arabidopsis mutants. Production of Rice transgenic lines is complex due to their poor regeneration ability and extended time for seed set. Most protocols follow the process of callus induction and Agrobacterium transfection followed by shoot and root regeneration. Here we generated a transgenic promoter reporter line for the promoter of WOX10 gene construct containing the OsWOX10_PRO fused with Page | 4 Page | 5

erYFP in the wild type (TP309) to show the expression and localization of WOX10 in roots, particularly in the crown roots and for further studies. Root zonation plays a crucial role in nutrient absorption and adventitious roots initiation, controlled by the phytohormones auxins and cytokinins. Previous studies suggest that auxin acts a crucial determinant of cell fate and regulates important stages of organ development such as cell cycle activation, cellular expansion and its differentiation.Although, it is speculated that auxin do no regulate these cellular processes directly, instead regulates cell fate by determining the level of PLETHORA (PLT) expression(Mähönen et al., 2014). Therefore, it can be concluded that root zonation is a result of cumulative effect of auxin gradient and PLTs levels inside a cell. So the thesis aimed at primer designing and cloning the promoter for rice PLT1 in the vector pCAMBIA1390erYFP, in order to study the gradient expression pattern of OsPLT1in various rice tissues.