Incomplete transfer of accessory loci influencing SbMATE expression underlies genetic background effects for aluminum tolerance in sorghum

Abstract

SUMMARYImpaired root development caused by aluminum (Al) toxicity is a major cause of grain yield reduction in crops cultivated on acid soils, which are widespread worldwide. In sorghum, the major Al-tolerance locus, Alt SB , is due to the function of SbMATE, which is an Al-activated root citrate transporter. Here we performed a molecular and physiological characterization of various Alt SB donors and near-isogenic lines harboring various Alt SB alleles. We observed a partial transfer of Al tolerance from the parents to the nearisogenic lines that was consistent across donor alleles, emphasizing the occurrence of strong genetic background effects related to Alt SB . This reduction in tolerance was variable, with a 20% reduction being observed when highly Al-tolerant lines were the Alt SB donors, and a reduction as great as 70% when other Alt SB alleles were introgressed. This reduction in Al tolerance was closely correlated with a reduction in SbMATE expression in near-isogenic lines, suggesting incomplete transfer of loci acting in trans on SbMATE. Nevertheless, Alt SB alleles from the highly Al-tolerant sources SC283 and SC566 were found to retain high SbMATE expression, presumably via elements present within or near the Alt SB locus, resulting in significant transfer of the Al-tolerance phenotype to the derived near-isogenic lines. Allelic effects could not be explained by coding region polymorphisms, although occasional mutations may affect Al tolerance. Finally, we report on the extensive occurrence of alternative splicing for SbMATE, which may be an important component regulating SbMATE expression in sorghum by means of the nonsense-mediated RNA decay pathway.

Reconstitution of CO2 Regulation of SLAC1 Anion Channel and Function of CO2-Permeable PIP2;1 Aquaporin as CARBONIC ANHYDRASE4 Interactor

“…consistent with other plant MATE transporters that upon expression produce anion currents in X. laevis oocytes (Maron et al, 2010;Melo et al, 2013). Our experiments do not exclude a role for RHC1 in CO 2 signaling (Tian et al, 2015) but point to the need to investigate whether previous findings might result at least in part from additive currents mediated by SLAC1 and RHC1.…”

Plant Adaptation to Acid Soils: The Molecular Basis for Crop Aluminum Resistance

“…However, normal frequency distributions in sorghum crosses where the Al resistance locus Alt SB plays a role in Al PP66CH23-Kochian ARI 15 January 2015 11:1 resistance (70) and the presence of apparent transgressive segregation suggest that a more complex inheritance pattern takes place in sorghum (9). Further support for this assertion is based on the incomplete transfer of Al resistance from parents to near-isogenic lines that has been observed in both sorghum (77) and wheat (40, 123). Additionally, in wheat, Ryan et al (110) have reported a second Al resistance mechanism (in addition to TaALMT1-mediated malate release) that involves citrate exudation controlled by a MATE homolog, indicating that there is more diversity in wheat Al resistance than initially thought.…”

“…Most importantly, the detection of transgressive segregation suggests that different Al resistance genes may act additively to result in high levels of sorghum Al resistance. A strong correlation has been found between SbMATE expression and Al resistance in sorghum (71,77), and additional loci acting via transcriptional regulation of SbMATE seem likely to play a role in sorghum Al resistance. When Melo et al (77) used marker-assisted backcrossing to transfer only the Alt SB locus from tolerant donors into an Alsensitive recurrent parent, they observed incomplete transfer of the Al resistance phenotype as well as reduced SbMATE expression in the derived near-isogenic lines harboring the Al-tolerant Alt SB alleles.…”

“…This approach allows for rapid screening of a large number of lines to identify the few Al-tolerant accessions (10), resulting in a substantial enrichment of accessions showing high or intermediate Al resistance. The final step is the confirmatory Al resistance phenotyping of selected accessions, which is necessary owing to background effects that may reduce SbMATE expression (77). If a breeding program does not contain Al-resistant sorghum accessions, introduction of known Al resistance donors followed by marker-assisted selection is advised.…”

Molecular mechanisms of Al tolerance in gramineous plants

“…Although the mechanisms regulating the expression level of ALMT and MATE/AACT have been elucidated in some species as described above, the whole picture on how these genes are regulated in different species and cultivars, remains to be further investigated in detail. Recently, Melo et al (2013) found that introduction of SbMATE into different background resulted in different expression level and Al tolerance, suggesting that SbMATE expression is regulated at multiple levels. It seems that both cis-and trans-acting elements are involved in regulating SbMATE expression.…”