AtWRKY70, encoding a WRKY transcription factor, is co-expressed with a set of Arabidopsis genes that share a pattern of RPP4- and RPP7-dependent late upregulation in response to Hyaloperonospora parasitica infection (LURP) genes. We show that AtWRKY70 is required for both full RPP4-mediated resistance and basal defense against H. parasitica. These two defense pathways are related to each other, because they require PAD4 and salicylic acid (SA). RPP7 function, which is independent from PAD4 and SA, is not affected by insertions in AtWRKY70. Although AtWRKY70 is required for RPP4-resistance, it appears not to contribute significantly to RPP4-triggered cell death. Furthermore, our data indicate that AtWRKY70 functions downstream of defense-associated reactive oxygen intermediates and SA. Constitutive and RPP4-induced transcript levels of two other LURP genes are reduced in AtWRKY70 T-DNA mutants, indicating a direct or indirect role for AtWRKY70 in their regulation. We propose that AtWRKY70 is a component of a basal defense mechanism that is boosted by engagement of either RPP4 or RPP7 and is required for RPP4-mediated resistance.