The wheat resistance gene Lr34 results in the constitutive induction of multiple defense pathways in transgenic barley
Chauhan H, Boni R, Bucher R, Kuhn B, Buchmann G, Sucher J, Selter LL, Hensel G, Kumlehn J, Bigler L, Glauser G, Wicker T, Krattinger SG and Keller B (2015) The wheat resistance gene Lr34 results in the constitutive induction of multiple defense pathways in transgenic barley. Plant Journal 84: 202-214.
The wheat gene Lr34 encodes an ABCG‐type transporter which provides durable resistance against multiple pathogens. Lr34
is functional as a transgene in barley, but its mode of action has
remained largely unknown both in wheat and barley. Here we studied gene
expression in uninfected barley lines transgenic for Lr34. Genes
from multiple defense pathways contributing to basal and inducible
disease resistance were constitutively active in seedlings and mature
leaves. In addition, the hormones jasmonic acid and salicylic acid were
induced to high levels, and increased levels of lignin as well as
hordatines were observed. These results demonstrate a strong,
constitutive re‐programming of metabolism by Lr34. The resistant Lr34 allele (Lr34res) encodes a protein that differs by two amino acid polymorphisms from the susceptible Lr34sus allele. The deletion of a single phenylalanine residue in Lr34sus was sufficient to induce the characteristic Lr34‐based responses. Combination of Lr34res and Lr34sus in the same plant resulted in a reduction of Lr34res expression by 8‐ to 20‐fold when the low‐expressing Lr34res line BG8 was used as a parent. Crosses with the high‐expressing Lr34res line BG9 resulted in an increase of Lr34sus expression by 13‐ to 16‐fold in progenies that inherited both alleles. These results indicate an interaction of the two Lr34 alleles on the transcriptional level. Reduction of Lr34res expression in BG8 crosses reduced the negative pleiotropic effects of Lr34res on barley growth and vigor without compromising disease resistance, suggesting that transgenic combination of Lr34res and Lr34sus can result in agronomically useful resistance.