TaBln1, a member of the Blufensin family, negatively regulates wheat resistance to stripe rust by reducing Ca(2+) influx

Blufensin1 (Bln1) has been identified as a susceptibility factor of basal defense mechanisms which is unique to the cereal grain crops barley (Hordeum vulgare), wheat (Triticum aestivum), rice (Oryza sativa), and rye (Secale cereale). However, the molecular mechanisms through which Bln1 regulates the wheat immune response are poorly understood. In this study, we found that TaBln1 was significantly induced by Puccinia striiformis f. sp. tritici (Pst) virulent race CYR31 infection. Knockdown of TaBln1 expression by virus-induced gene silencing reduced Pst growth and development, and enhanced the host defense response. In addition, TaBln1 was found to physically interact with a calmodulin, TaCaM3, on the plasma membrane. Silencing TaCaM3 with virus-induced gene silencing increased fungal infection areas and sporulation and reduced wheat resistance to the Pst avirulent race CYR23 (incompatible interaction) and virulent race CYR31 (compatible interaction). Moreover, we found that the accumulation of TaCaM3 transcripts could be induced by treatment with chitin but not flg22. Silencing TaCaM3 decreased the calcium (Ca(2+)) influx induced by chitin, but silencing TaBln1 increased the Ca(2+) influx in vivo using a noninvasive micro-test technique. Taken together, we identified the wheat susceptibility factor TaBln1, which interacts with TaCaM3 to impair Ca(2+) influx and inhibit plant defenses.