Figure 6.

The LAS Gene Mediates YAB1-Derived Signals.

(A) to (F) Effect of the las-11 mutant on flowers with altered levels of YAB1 activity.

(A) PAP1:YAB3 flower with one sepal removed revealing additional petals, additional stamens, and disrupted gynoecium development.

(B) las-11 PAP1:YAB3 flower with a nearly normal number of petals and stamens (one sepal removed).

(C) PAP3:YAB3 flower with additional stamens and disrupted gynoecium development (one sepal removed).

(D) las-11 PAP3:YAB3 flower with a near wild-type appearance (one sepal removed).

(E) fil-8 inflorescence.

(F) las-11 fil-8 inflorescence, comprising primarily filamentous flowers.

(G) to (R) Distribution of PLAS≫LAS-GFP fluorescence. Transverse ([G] and [I]) and longitudinal ([H] and [J]) sections through LAS≫LAS-GFP inflorescences ([G] and [H]) and flowers ([I] and [J]). Transverse section of a fil-8 PLAS≫LAS-GFP inflorescence (K) and longitudinal section of a flower (L) with expression between the floral organs and the FM (b, bract). Transverse section of a fil-8 yab3-2 PLAS≫LAS-GFP inflorescence (M) and longitudinal section of a flower (N) with almost no expression between the sepal and the FM. Transverse section of a PAP1:YAB3 PLAS≫LAS-GFP inflorescence (O) and longitudinal section of a flower (P) with significant expansion of the LAS≫LAS-GFP expression domain marked by arrows. Longitudinal section through stage 4 wild-type (Q) and PAP3:YAB3 (R) flowers, where expansion of PLAS≫LAS-GFP expression is marked with arrows.

(S) A model of IM expression territories. A representation of the expression domains of genes examined in this study and the direction of influence (arrows) established or speculated based on the results. PLAS≫LAS-GFP signal is present, while the others have been painted in as representative domains. Primordial YAB1 activity (pink) nonautonomously communicates with the floral (FM) and inflorescence (IM) meristems and regulates the expression of CLV3 (purple) and WUS (yellow). LAS, acting at the organ-meristem boundary (bou), mediates this signaling process. cb, cryptic bract.

Asterisks indicate the sepal. Numbers represent the order of flower initiation. Bars = 1 mm in (A) to (F) and 50 μm in (G) to (R).