Coat a 9 x 5-inch loaf pan with cooking spray. Line pan with parchment paper, and coat with cooking spray.
Weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours and next 6 ingredients (through salt). Combine buttermilk and egg; add to flour mixture. Stir just until combined.
Spoon mixture into prepared pan. Bake at 325 for 1 hour and 5 minutes or until wooden pick inserted in center comes out clean. Invert bread onto a wire rack; cool completely. Remove parchment; slice bread into 12 slices.