Based on complementary vascular and leaf phenotypes of class III HD-ZIP and KANADI mutants, we propose that a common genetic program dependent upon miRNAs governs adaxial-abaxial patterning of leaves and radial patterning of stems in the angiosperm shoot. This finding implies that a common patterning mechanism is shared between apical and vascular meristems.

The upper side of the angiosperm leaf is specialized for efficient capture of sunlight whereas the lower side is specialized for gas exchange. In Arabidopsis, the establishment of polarity in the leaf probably requires the generation and perception of positional information along the radial (adaxial versus abaxial or central versus peripheral) dimension of the plant. This is because the future upper (adaxial) side of the leaf develops from cells closer to the centre of the shoot, whereas the future under (abaxial) side develops from cells located more peripherally. Here we implicate the Arabidopsis PHABULOSA and PHAVOLUTA genes in the perception of radial positional information in the leaf primordium. Dominant phabulosa (phb) and phavoluta (phv) mutations cause a dramatic transformation of abaxial leaf fates into adaxial leaf fates. They do so by altering the predicted sterol/lipid-binding domains of ATHB14 and ATHB9, proteins of previously unknown function that also contain DNA-binding motifs. This change probably renders the protein constitutively active, implicating this domain as a central regulator of protein function and the PHB and PHV proteins as receptors for an adaxializing signal.

The fruit, which mediates the maturation and dispersal of seeds, is a complex structure unique to flowering plants. Seed dispersal in plants such as Arabidopsis occurs by a process called fruit dehiscence, or pod shatter. Few studies have focused on identifying genes that regulate this process, in spite of the agronomic value of controlling seed dispersal in crop plants such as canola. Here we show that the closely related SHATTERPROOF (SHP1) and SHATTERPROOF2 (SHP2) MADS-box genes are required for fruit dehiscence in Arabidopsis. Moreover, SHP1 and SHP2 are functionally redundant, as neither single mutant displays a novel phenotype. Our studies of shp1 shp2 fruit, and of plants constitutively expressing SHP1 and SHP2, show that these two genes control dehiscence zone differentiation and promote the lignification of adjacent cells. Our results indicate that further analysis of the molecular events underlying fruit dehiscence may allow genetic manipulation of pod shatter in crop plants.

Highlights d Long-read sequencing of 100 tomato genomes uncovered 238,490 structural variants d Transposons underlie many SVs, and SV hotspots revealed large introgressions d SVs associated with genes are predictive of population-scale changes in expression d New genome assemblies resolved complex breeding QTLs caused by SVs

Several indications implied that the Arabidopsis FT ( FLOW-ERING LOCUS T) gene provides a possible functional link between the systemic pathways and the cell-autonomous pathways to flowering. FT is a major integrator of the genetic pathways to flowering in short and long days (4, 5); it encodes a signaling factor (6, 7) and is not expressed in the SAM proper (8) but can be detected, upon induction, in shoot apices (SAPs) containing young leaves (9). Flowering is delayed in mutant ft plants (10, 11), and when FT is overexpressed, flowering occurs earlier with a determinate inflorescence (12, 13). FT is regulated by the flowering-time gene CONSTANS in both long-and short-day plants (14,15), and grafting experiments in Arabidopsis have shown that systemic induction of flowering by CONSTANS is most likely mediated by FT (16,17). It was recently shown that a small fraction of heat-shock-induced FT RNA, originating in a single leaf, is found in the SAPs, suggesting that the FT mRNA itself may represent a major component of florigen (18).We chose tomato, a photoperiod-insensitive plant, to test the premise that orthologs of the Arabidopsis FT gene can initiate a conserved, long-distance, flower-promoting pathway in diverse flowering systems. The generality of the florigen hypothesis was supported by interspecies grafting experiments (2). Grafting results are independent of the validity of promoters, the resolution of in situ hybridization patterns, inferences derived from the activation of upstream genes, or interpretations of clonal analysis. The perennial habit; the compound shoots, which permit the analysis of multiple vegetative͞floral transition events in one plant (19); and the ease of grafting render tomato as a useful experimental platform for investigating the nature of florigen. We expanded the analysis in tomato with parallel experiments in long-day Arabidopsis and short-day tobacco.The primary shoot of tomato is terminated by an inflorescence, after which the apparent main axis consists of an upright array of reiterated axillary branches called sympodial units (SUs). Each SU arises from the most proximal axillary bud of the preceding unit and consists of three vegetative nodes and a terminal inflorescence (Fig. 1A). The distinction between the primary and compound sections of sympodial plants provides two basic criteria for flowering time: the number of leaves to the first inflorescence in the primary shoot and the number of leaves between inflorescences in the compound part. Here, we identify the tomato FT ortholog as SINGLE FLOWER TRUSS (SFT), a gene regulating primary shoot flowering time, sympodial habit, and flower morphology. All aspects of the sft phenotype were complemented by graft-transmissible SFT signals, suggesting that all are the consequence of a common flowering-time defect. Significantly, graft-transmissible SFT signals substituted for light dose and two inductive photoperiodic stimuli in different species as well. ResultsThe Tomato Ortholog of FT Is Disrupted in Late-Flowering sft Mutants....