Repression of Floral Meristem Fate Is Crucial in Shaping Tomato Inflorescence

Tomato is an important crop and hence there is a great interest in understanding the genetic basis of its flowering. Several genes have been identified by mutations and we constructed a set of novel double mutants to understand how these genes interact to shape the inflorescence. It was previously suggested that the branching of the tomato inflorescence depends on the gradual transition from inflorescence meristem (IM) to flower meristem (FM): the extension of this time window allows IM to branch, as seen in the compound inflorescence (s) and falsiflora (fa) mutants that are impaired in FM maturation. We report here that JOINTLESS (J), which encodes a MADS-box protein of the same clade than SHORT VEGETATIVE PHASE (SVP) and AGAMOUS LIKE 24 (AGL24) in Arabidopsis, interferes with this timing and delays FM maturation, therefore promoting IM fate. This was inferred from the fact that j mutation suppresses the high branching inflorescence phenotype of s and fa mutants and was further supported by the expression pattern of J, which is expressed more strongly in IM than in FM. Most interestingly, FA - the orthologue of the Arabidopsis LEAFY (LFY) gene - shows the complementary expression pattern and is more active in FM than in IM. Loss of J function causes premature termination of flower formation in the inflorescence and its reversion to a vegetative program. This phenotype is enhanced in the absence of systemic florigenic protein, encoded by the SINGLE FLOWER TRUSS (SFT) gene, the tomato orthologue of FLOWERING LOCUS T (FT). These results suggest that the formation of an inflorescence in tomato requires the interaction of J and a target of SFT in the meristem, for repressing FA activity and FM fate in the IM

Revisiting the involvement of SELF-PRUNING in the sympodial growth of tomato.

peer reviewe

Revisiting the Involvement of SELF-PRUNING in the Sympodial Growth of Tomato1[W]

peer reviewe

Inflorescence phenotype of tomato mutants.

<p>(A–C) Ailsa Craig WT; (D) and (E) <i>s</i> mutant; (F) and (G) <i>j</i> mutant; (H) and (I) <i>j∶s</i> double mutant; (J–L) <i>fa</i> mutant; (M–O) <i>s∶fa</i> double mutant; (P) and (Q) <i>j∶fa</i> double mutant. In microscopic pictures, colour bars show the clefts that occurred sequentially when new meristems were initiated to build-up the inflorescence. Red: 1^st; yellow: 2^nd; green: 3^rd; blue: 4^th; purple: 5^th. Dots of same colours show the corresponding branching in macroscopic inflorescence pictures. Pictures K and N zoom in J and M, respectively, to show clumps of IMLs in the inflorescences (arrows). Genotype abbreviations: AC, Ailsa Craig WT; <i>fa</i>, <i>falsiflora</i>; <i>j</i>, <i>jointless</i>; <i>s</i>, <i>compound inflorescence</i>. Annotations: AX, axillary meristem; F, flower; FM, flower meristem; IM, inflorescence meristem; IML, IM-like; L, leaf; SAM, shoot apical meristem; SYM, sympodial meristem; VM, vegetative meristem. Bars = 100 µm except in K and N where bars = 1 mm.</p

Flowering time (expressed as number of leaves below the first inflorescence) of tomato double mutants.

<p>(A) <i>j∶sft</i>; (B) <i>s∶sft</i>; (C) <i>j∶fa</i>; (D) <i>s∶fa</i>; (E) <i>j∶s</i>; and (F) <i>fa∶sft</i>. Values followed by a same letter (a, b, or c) are not statistically different (P<0.05). Genotype abbreviations: AC, Ailsa Craig WT; <i>fa</i>, <i>falsiflora</i>; Hz, Heinz WT; <i>j, jointless</i>; Pl, Platense WT; RR, Rheinlands Rhum WT; <i>s</i>, <i>compound inflorescence</i>; <i>sft</i>, <i>single flower truss</i>. The <i>j</i> mutant is in AC background in A and C, in Hz background in E.</p

Tomato double mutants produced and analysed in this study.

<p>Tomato double mutants produced and analysed in this study.</p

Inflorescence phenotype of tomato mutants.

<p>(A) and (B) Inflorescence of <i>sft</i> mutant showing several flowers; (C) and (D) Inflorescence of <i>sft</i> mutant with solitary flower; (E–G) <i>s∶sft</i> double mutant; (H) and (I) <i>fa∶sft</i> double mutant; (J) and (K) <i>j∶sft</i> double mutant. In microscopic pictures, colour bars show the clefts that occurred sequentially when new meristems were initiated to build-up the inflorescence. Red: 1^st; yellow: 2^nd, green: 3^rd. Dots of same colours show the corresponding branching in macroscopic inflorescence picture. In C and J, arrows point at leaf-like sepals. Genotype abbreviations: <i>fa</i>, <i>falsiflora</i>; <i>j</i>, <i>jointless</i>; <i>s</i>, <i>compound inflorescence</i>; <i>sft</i>, <i>single flower truss.</i> Annotations: F, flower; FM, flower meristem; IM, inflorescence meristem; IML, IM-like; L, leaf; S, shoot; SYM, sympodial meristem; VM, vegetative meristem. Bars = 100 µm.</p