4-(Indol-3-ylmethyl)-4-hydroxy-2-oxoglutarate, which is useful as an intermediate in the synthesis of monatin, may be synthesized from indole pyruvic acid and pyruvic acid (and/or oxaloacetic acid) by using a novel aldolase derived from the genus Pseudomonas, Erwinia, Flavobacterium, or Xanthomonas.