Early Seedling Screening Reveals Unidentified Al Resistance Mechanisms in Lithuanian Barley Cultivars

TL;DR

This study identifies new resistance mechanisms to aluminum toxicity in Lithuanian barley cultivars using early seedling screening and gene expression analysis.

Contribution

The study reveals previously unknown regulatory mechanisms of Al resistance in barley, including HvAACT1 and aquaporin TIP4;1 gene expression.

Findings

Morphometric parameters were more effective than biochemical assays for early screening of Al resistance in barley.

The modern barley cultivar 'Ema DS' showed the highest Al resistance with a root tolerance index of 0.86.

HvAACT1 and aquaporin TIP4;1 were significantly upregulated in 'Ema DS', indicating new detoxification mechanisms.

Abstract

Aluminum toxicity in acidic soils represents a significant environmental stressor that affects yields worldwide and is only expected to worsen. Breeding resistant varieties remains the most viable solution; however, fast and robust procedures to determine cultivar viability must be developed and applied to promising genotypes. This study explored historical and modern Lithuanian-bred barley cultivars using morphometrical and biochemical markers for Al resistance and sequence and expression analyses of potential candidate genes. Morphometric seedling measurements (relative root length reduction −13.65 ± 0.33% (p < 0.001) and root tolerance index 0.86 ± 0.44 after 72 h at 8 mM Al stress) revealed the modern cv. ‘Ema DS’ to be the most Al resistant, while biochemical assays offered a poor distinction between the Al-resistant and sensitive cultivars. Thus, we determined that morphometric parameters were more effective in the early screening for barley Al resistance. The genetic screening of well-established Al resistance markers in the barley citrate transporter HvAACT1 revealed a mismatch between the observed barley phenotypes and genotypes. Further testing was conducted through expression analyses of HvAACT1 and seven aquaporin family genes, which revealed a correlation between the best empirical performance in cv. ‘Ema DS’ and a high HvAACT1 (2.02 fold change, p < 0.05) expression, despite the lack of established genetic markers, as well as a stress-induced significant upregulation of aquaporin TIP4;1 (2.45 fold change, p < 0.05), suggesting previously undiscovered regulatory mechanisms of external and internal detoxification influencing Al resistance in Lithuanian barley cultivars, as well as potential future candidates for Al-resistant barley breeding programs.

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