A 23-kDa, root exudate polypeptide co-segregates with aluminum resistance in Triticum aestivum

We previously reported that treatment with aluminum (Al) leads to the accumulation of several polypeptides (12-, 23-, and 43.5-kDa) in root exudates of an Al-resistant cultivar of Triticum aestivum. In this report, we examine the segregation of the 23-kDa, Al-induced polypeptide and the Al-resistant phenotype in single F-2 plants arising from a cross between Al-resistant and Al-sensitive doubled-haploid (DH) lines. Single plants and plant populations were screened for sensitivity/resistance to Al using synthesis of 1,3-beta-glucans (callose) as a sensitive marker for Al injury. Callose production in the Al-sensitive cv. Katepwa was approximately 3-fold higher than observed in the Al-resistant cv. Maringa, or a near-isogenic line derived from Katepwa and Maringa (Alikat), over a broad range of Al concentrations (0-100 mu M), Similar results were observed with DH lines developed from cv, Katepwa, which produced two-four times more callose than DH lines developed from cv, Alikat, When single plants from F-1 and F-2 populations derived from a cross between DH Katepwa and DH Alikat were scored for Al-induced callose production after 4 days exposure to 100 mu M Al, all F-1 plants were Al-resistant and F-2 plants segregated approximately 3:1 for Al-resistance/sensitivity. A backcross population derived from crossing Al-resistant F, with Al-sensitive Katepwa, segregated 1:1 for Al-resistance/sensitivity. Thus, the Al-resistant phenotype is inherited in a monogenic, dominant fashion in our DH lines, Enhanced accumulation of the Al-induced, 23-kDa polypeptide in root exudates was a trait which co-segregated with the Al-resistant phenotype in F, populations. This polypeptide was strongly labeled with S-35-methionine after 3 days of Al exposure and 6 h labeling. When root exudate polypeptides were separated by immobilized metal ion affinity chromatography, the 23-kDa polypeptide demonstrated significant Al-binding capacity. This polypeptide has been purified to near-homogeneity, providing an opportunity to isolate the gene(s) encoding this polypeptide.