Fig. 4.

Nicotiana attenuata polyketide synthase 2 (NaPKS2) is the enzyme that participates in benzylacetone (BA) biosynthesis in N. attenuata flowers. (a) NaPKS2 and NaPKS3 are co‐silenced in NaPKS2/3‐silenced corollas. Green fluorescent protein (GFP), plant infected TRV2‐GFP (a truncated form), which was used as a negative control; VIGS‐PKS, a NaPKSs co‐silenced plant, which was generated by virus‐induced gene silencing (VIGS) (mean ± SD; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001; two‐tailed Student’s t‐test). Mean (±SD) levels of headspace BA show that NaPKS2/3‐silenced flowers emit less BA. (b) NaPKS2/3‐silenced flowers harbor less endogenous BA in corolla tissue. (mean ± SD; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001; two‐tailed Student’s t‐test). (c) In vitro enzyme assay reveals that NaPKS2, not NaPKS3, can synthesize benzalacetone, a putative intermediate of BA biosynthesis. A novel peak detected in NaPKS2‐contained reaction mixtures represents benzalacetone, based on its fragmentation pattern and standard compound injections.