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 Arabidopsis 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 IDL genes in soybean. In the present study, the functions of two root-specific expressed IDL genes, GmIDL2a and GmIDL4a, are investigated. The expressions of GmIDL2a and GmIDL4a, induced by auxin, are located in the overlaying tissue, where LRs are initiated. Overexpression of GmIDL2a and GmIDL4a increases the LR densities of the primary roots, but not in the elder root. Abnormal cell layer separation has also been observed in GmIDL2a- and GmIDL4a-overexpressing roots. These results suggest that the overlaying tissues of GmIDL2a- and GmIDL4a-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 GmIDL2a and GmIDL4a are overexpressed in hairy roots. Here, we conclude that GmIDL2a and GmIDL4a function in LR emergence through regulating soybean CWR gene expression.
Highlights
Root system architecture represents a key adaptability, enabling plants to cope with abiotic stresses such as drought, nutrient deficiency, and salinity, and is very important for plant growth and development
It has been reported that IDA is associated with floral organ abscission, and controls the separation step of the overlaying tissues during lateral roots (LRs) emergence, suggesting the vital role of the IDA ligand in the IDA–HAE/HSL2 signaling pathway [18,32]
Besides IDA in Arabidopsis, the other five IDL genes have been identified through a tBLASTn search using the conserved EPIP motif of the IDA protein, which is sufficient to induce abscission through its receptor HAE/HAL2 [18,28]
Summary
Root system architecture represents a key adaptability, enabling plants to cope with abiotic stresses such as drought, nutrient deficiency, and salinity, and is very important for plant growth and development. Further anticlinal and periclinal divisions produce a dome-shaped LRP that divides progressively as the primary root meristem. This process is associated with auxin transport [7,8,9,10], auxin signaling [11,12], and oscillations of the auxin responses [9]. 12 GmIDL genes have been identified in the soybean genome, in which GmIDL2a and GmIDL4a were highly expressed in the root [27]. The overexpression of GmIDL2a and GmIDL4a can accelerate the emergence of LRPs in primary roots. Abnormal cell layer separation was observed in elder roots when GmIDL2a and GmIDL4a were overexpressed. Our results enhanced the understanding of soybean LR emergence and indicated a potential use of these genes in soybean root architecture improvement
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