Identification and characterization of novel QTL conferring internal detoxification of aluminum in soybean.

Aluminum (Al) toxicity inhibits soybean root growth, leading to insufficient water and nutrient uptake. In this research, two soybean lines (Magellan and PI 567731) were identified differing in Al tolerance as determined by primary root length ratio (PRL_Ratio), total root length ratio (TRL_Ratio), and root tip number ratio (RTN_Ratio) under Al stress compared to unstressed controlled conditions. Serious root necrosis was observed in PI 567731, but not in Magellan under Al stress. An F8 recombinant inbred line population derived from a cross between Magellan and PI 567731 was used to map the quantitative trait loci (QTL) for Al-tolerance. Three QTL on chromosomes 3, 13, and 20, with tolerant-alleles from Magellan, were identified. qAl_Gm13 and qAl_Gm20, explained large phenotypic variations (13-27%) and played roles in maintaining root elongation. qAl_Gm03 was involved in maintaining root initiation under Al stress. These results suggested the importance of using the parameters of root elongation and root initiation in Al tolerance studies. In addition, qAl_Gm13 and qAl_Gm20 were confirmed in near-isogenic backgrounds and were identified to epistatically regulate Al tolerance in internal detoxification instead of Al 3+ exclusion. The candidate genes for qAl_Gm13 and qAl_Gm20 were suggested by analyzing a previous RNA-seq study. Phylogenetic and pedigree analysis identified the tolerant alleles of both loci derived from the US ancestor line, A.K.[FC30761], originally from China. Our results provide novel genetic resources for breeding Al-tolerant soybeans and suggest that the internal detoxification contributes to soybean tolerance to excessive soil Al.