The tomato Blind gene encodes a MYB transcription factor that controls the formation of lateral meristems

Abstract

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...

Two-Step Regulation ofLAX PANICLE1Protein Accumulation in Axillary Meristem Formation in Rice

“…LS, LAS, and MOC1 are orthologous genes encoding transcriptional regulators of the GRAS family (Schumacher et al, 1999;Greb et al, 2003;Li et al, 2003). BL and RAX are also orthologous genes that encode R2R3-type Myb transcription factors (Schmitz et al, 2002;Keller et al, 2006;Mü ller et al, 2006). This shows that AM formation may be regulated by a conserved mechanism in different plant species, including monocots and eudicots.…”

“…Therefore, the defective genes in these mutants are probably involved in mechanisms that control general aspects of meristem initiation or function unless AM formation is affected as a secondary consequence of these mutations. The other class of mutants, comprising Arabidopsis thaliana lateral suppressor (las) and regulator of axillary meristem (rax) mutants, tomato (Solanum lycopersicum) lateral suppressor (ls) and blind (bl), maize (Zea mays) barren stalk1 (ba1), and rice (Oryza sativa) monoculm1 (moc1) and lax panicle1 (lax1) show AM-specific defects (Schumacher et al, 1999;Komatsu et al, 2001Komatsu et al, , 2003Ritter et al, 2002;Schmitz et al, 2002;Greb et al, 2003;Li et al, 2003;Keller et al, 2006;Mü ller et al, 2006). These AM-specific mutants can be further divided into two classes: either the mutant shows developmental specific defects or all AMs are affected regardless of the plant's developmental stage.…”

Hormonal Regulation of Branching in Grasses

“…The NAC domain transcription factors CUC1,2,3 play a role in axillary meristem initiation in Arabidopsis, but in rice, overexpression of OsTIL1 enhances axillary meristem outgrowth rather than initiation (Vroemen et al, 2003;Hibara et al, 2006;Mao et al, 2007;Raman et al, 2008). R2 R3 Myb transcription factors RAX1,2,3/BLIND (Schmitz et al, 2002;Keller et al, 2006;Muller et al, 2006) play a role in eudicots, but a homolog in monocots has not yet been identified. Therefore, the roles of these transcription factors still need to be clarified in monocots.…”

The Barley Uniculme4 Gene Encodes a BLADE-ON-PETIOLE-Like Protein That Controls Tillering and Leaf Patterning

“…However, the molecular mechanisms that control branching in eudicots are not completely conserved with tiller development in grasses (Kebrom et al, 2013;Hussien et al, 2014;Waldie et al, 2014). For example, the reduced-branching mutations in the REGULATOR OF AXILLARY MERISTEMS1, REGULATOR OF AX-ILLARY MERISTEMS2, REGULATOR OF AXILLARY MERISTEMS3, and BLIND genes of Arabidopsis and tomato (Schmitz et al, 2002;Keller et al, 2006;Müller et al, 2006) are conserved in eudicots but have not been identified in monocot genomes (Keller et al, 2006;Müller et al, 2006).…”