GmIDL2a and GmIDL4a, Encoding the Inflorescence Deficient in Abscission-Like Protein, Are Involved in Soybean Cell Wall Degradation during Lateral Root Emergence

Abstract

The number of lateral roots (LRs) of a plant determines the efficiency of water and nutrient uptake. Soybean is a typical taproot crop which is deficient in LRs. The number of LRs is therefore an important agronomic trait in soybean breeding. It is reported that the inflorescence deficient in abscission (IDA) protein plays an important role in the emergence of <i>Arabidopsis</i> LRs. Previously, the genes which encode IDA-like (IDL) proteins have been identified in the soybean genome. However, the functions of these genes in LR development are unknown. Therefore, it is of great value to investigate the function of <i>IDL</i> genes in soybean. In the present study, the functions of two root-specific expressed <i>IDL</i> genes, <i>GmIDL2a</i> and <i>GmIDL4a</i>, are investigated. The expressions of <i>GmIDL2a</i> and <i>GmIDL4a</i>, induced by auxin, are located in the overlaying tissue, where LRs are initiated. Overexpression of <i>GmIDL2a</i> and <i>GmIDL4a</i> increases the LR densities of the primary roots, but not in the elder root. Abnormal cell layer separation has also been observed in <i>GmIDL2a</i>- and <i>GmIDL4a</i>-overexpressing roots. These results suggest that the overlaying tissues of <i>GmIDL2a</i>- and <i>GmIDL4a</i>-overexpressing roots are looser and are suitable for the emergence of the LR primordium. Further investigation shows that the expression of some of the cell wall remodeling (CWR) genes, such as xyloglucan endotransglucosylase/hydrolases, expansins, and polygalacturonases, are increased when <i>GmIDL2a</i> and <i>GmIDL4a</i> are overexpressed in hairy roots. Here, we conclude that <i>GmIDL2a</i> and <i>GmIDL4a</i> function in LR emergence through regulating soybean <i>CWR</i> gene expression.