Abstract
Aluminum (Al) toxicity on acid soils adversely affects maize yields, which can be overcome by combining soil amendments with genetic tolerance. In maize, ZmMATE1 confers Al tolerance via Al-activated citrate release, whereby citrate forms non-toxic complexes with Al3+ in the rhizosphere. Here, we investigated Al tolerance mechanisms in maize germplasm originated from Kenya based on quantitative trait loci (QTL) mapping. Five QTLs and four epistatic interactions explained ~51% of the phenotypic variation for Al tolerance. The lack of Al tolerance QTL on chromosome 6 and the much lower expression of ZmMATE1 in both Kenyan lines than in Cateto Al237, which donates the superior allele of ZmMATE1, strongly indicate that this gene does not play a significant role in Al tolerance in neither parent. In turn, maize homologs to genes previously implicated in Al tolerance in other species, ZmNrat1, ZmMATE3, ZmWRKY and ZmART1, co-localized with Al tolerance QTL and were more highly expressed in the parent that donate favorable QTL alleles. However, these candidate genes will require further studies for functional validation on maize Al tolerance. The existence of Al tolerance mechanisms independent from ZmMATE1 suggests it is possible to develop highly Al tolerant cultivars by pyramiding complementary Al tolerance genes in maize.
Highlights
Aluminum (Al) toxicity on acid soils adversely affects maize yields, which can be overcome by combining soil amendments with genetic tolerance
Significant genotypic variation was detected for Al tolerance in F2:3 progeny derived from 203B-14 (Al tolerant) crossed with SCH3 (Al sensitive) based on relative net root growth (RNRG) (Supplementary Table S1)
Several landraces collected at maize growing areas in Kenya showed high levels of Al tolerance in nutrient solution, including 203B, which was originated from an acid soil region in Muranga County[19]
Summary
Aluminum (Al) toxicity on acid soils adversely affects maize yields, which can be overcome by combining soil amendments with genetic tolerance. The lack of Al tolerance QTL on chromosome 6 and the much lower expression of ZmMATE1 in both Kenyan lines than in Cateto Al237, which donates the superior allele of ZmMATE1, strongly indicate that this gene does not play a significant role in Al tolerance in neither parent. Maize homologs to genes previously implicated in Al tolerance in other species, ZmNrat[1], ZmMATE3, ZmWRKY and ZmART1, co-localized with Al tolerance QTL and were more highly expressed in the parent that donate favorable QTL alleles. The present study aimed at identifying QTL and candidate genes associated with these mechanisms in an F2:3 population derived from the highly Al-tolerant Kenyan line, 203B-14, crossed with SCH3 (Al-sensitive)
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