The multitude of forms observed in flowering plants is largely because of their ability to establish new axes of growth during postembryonic development. This process is initiated by the formation of secondary meristems that develop into vegetative or reproductive branches. In the blind and torosa mutants of tomato, initiation of lateral meristems is blocked during shoot and inflorescence development, leading to a strong reduction in the number of lateral axes. In this study, it is shown that blind and torosa are allelic. The Blind gene has been isolated by positional cloning, and it was found that the mutant phenotype is caused by a loss of function of an R2R3 class Myb gene. RNA interference-induced blind phenocopies confirmed the identity of the isolated gene. Double mutant analysis shows that Blind acts in a novel pathway different from the one to which the previously identified Lateral suppressor gene belongs. The findings reported add a new class of transcription factors to the group of genes controlling lateral meristem initiation and reveal a previously uncharacterized function of R2R3 Myb genes.I n flowering plants, postembryonic shoot development is controlled by the activity of the shoot apical meristem (SAM). The SAM established during embryogenesis produces in a regular fashion leaf, node, and internode primordia, which generate the primary shoot of a plant. Secondary meristems arise in the axils of leaves as well as on the flanks of the inflorescence meristems. Lateral meristems produced during the vegetative phase develop into shoots repeating, at least in part, the growth pattern of the primary shoot, whereas after floral transition lateral meristems develop into flowers or new inflorescence axes.In Arabidopsis thaliana, Zea mays, and several other plant species, genes have been isolated that are required for SAM initiation, maintenance, and function, and interactions between these genes are being studied (1). However, much less is known about the genetic control of lateral meristem initiation and function during shoot and inflorescence development. In tomato, lateral meristems are formed in all leaf axils and are first detectable in the axil of the fifth youngest primordium (2). They develop into fast-growing side shoots that give the plant a bushy appearance. Whereas in many higher plants the primary SAM remains active throughout the entire lifespan, in tomato, it is transformed into a terminal inflorescence, and the uppermost axillary meristem takes over its function to continue the main stem. After formation of three leaves, this sympodial shoot terminates itself in an inflorescence, and sympodial shoots of progressively higher order elongate the main axis (3, 4). The tomato inf lorescence has been described as a cyme, i.e., flowers arise as terminal structures, and the inflorescence axis grows because of a lateral meristem, which will again be transformed into a floral meristem and so on (3). Recent analysis has in part modified this view by demonstrating that the inflorescence meristem is s...

The DNA sequence of the terminal 4.2 kilobases (kb) of the 30-kb insertion in the endosperm sucrose synthase gene of maize mutant sh-m5933 shows that it comprises two identical 2,040-base pair (bp) segments, one inserted in the reverse direction into the other. We suggest that the 2,040-bp sequence is an example of the transposable element Dissociation described by Barbara McClintock.

IS-elements are devoid of easily recognizable transacting functions and exert their visible effects in the position cis only (recent reviews Calos and Miller 1980; Starlinger 1980). It has been a matter of debate, whether these elements encode functions for their own transposition. In the case of the E. coli IS-elements this could not easily be determined by genetic methods, because most of these elements are present in several copies (Saedler and Heiss 1973; Deonier et al. 1979). In the case of the IS-elements flanking transposons, evidence has recently been brought forward that these carry the transposition specificity (Rothstein et al. 1980; Kleckner 1980; Grindley 1981). IS4 is present in one copy only in several E. coli K12 strains and should, therefore, be suitable for genetic and physiological studies (Chadwell et al. 1979). It has been cloned from several sites on the E. coli chromosome in pBR322 (Klaer and Starlinger 1980). Here we report the DNA sequence of IS4 which contains an open reading frame for 442 amino acids, and of the junctions of this element with surrounding DNA at three different sites in the E. coli chromosome.

A cDNA clone for maize endosperm sucrose synthetase of 62o nucleotide pairs length was obtained by cloning double stranded DNA obtained from the total maize endosperm poly(A)RNA in pBR322, and identifying the appropriate clone by hybrid-promoted translation.In Southern blotting to genomic BamHI-digested DNA, a single band only of-v2o Kb lights up, indicating that the sucrose syn-