Physiological Changes in Barley <i>mlo-11</i> Powdery Mildew Resistance Conditioned by Tandem Repeat Copy Number
Wild barley accessions have evolved broad-spectrum defence against barley powdery mildew through recessive <i>mlo</i> mutations. However, the <i>mlo</i> defence response is associated with deleterious phenotypes with a cost to yield and fertility, with implications for natura...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2020-11-01
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| Series: | International Journal of Molecular Sciences |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1422-0067/21/22/8769 |
| Summary: | Wild barley accessions have evolved broad-spectrum defence against barley powdery mildew through recessive <i>mlo</i> mutations. However, the <i>mlo</i> defence response is associated with deleterious phenotypes with a cost to yield and fertility, with implications for natural fitness and agricultural productivity. This research elucidates the mechanism behind a novel <i>mlo</i> allele, designated <i>mlo-11</i>(<i>cnv2</i>), which has a milder phenotype compared to standard <i>mlo-11</i>. Bisulphite sequencing and histone ChIP-seq analyses using near-isogenic lines showed pronounced repression of the <i>Mlo</i> promoter in standard <i>mlo-11</i> compared to <i>mlo-11</i>(<i>cnv2</i>), with repression governed by 24 nt heterochromatic small interfering RNAs. The <i>mlo-11</i>(<i>cnv2</i>) allele appears to largely reduce the physiological effects of <i>mlo</i> while still endorsing a high level of powdery mildew resistance. RNA sequencing showed that this is achieved through only partly restricted expression of <i>Mlo</i>, allowing adequate temporal induction of defence genes during infection and expression close to wild-type <i>Mlo</i> levels in the absence of infection. The two <i>mlo-11</i> alleles showed copy number proportionate oxidase and peroxidase expression levels during infection, but lower amino acid and aromatic compound biosynthesis compared to the null allele <i>mlo-5</i>. Examination of highly expressed genes revealed a common WRKY W-box binding motif (consensus ACCCGGGACTAAAGG) and a transcription factor more highly expressed in <i>mlo-11</i> resistance. In conclusion, <i>mlo-11</i>(<i>cnv2</i>) appears to significantly mitigate the trade-off between <i>mlo</i> defence and normal gene expression. |
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| ISSN: | 1661-6596 1422-0067 |