The Lateral suppressor (Ls) gene of tomato encodes a new member of the VHIID protein family

Abstract

The ability of the shoot apical meristem to multiply and distribute its meristematic potential through the formation of axillary meristems is essential for the diversity of forms and growth habits of higher plants. In the lateral suppressor mutant of tomato the initiation of axillary meristems is prevented, thus offering the unique opportunity to study the molecular mechanisms underlying this important function of the shoot apical meristem. We report here the isolation of the Lateral suppressor gene by positional cloning and show that the mutant phenotype is caused by a complete loss of function of a new member of the VHIID family of plant regulatory proteins.

Figure 1

Physical map of the Ls region. (A) Schematic representation of the cosmid contig around the Ls locus. The YAC and cosmid clones are shown as horizontal lines. The dashed vertical lines indicate the approximate positions of recombination breakpoints. Open boxes represent cDNAs, and flanking restriction fragment length polymorphism markers are displayed as shaded boxes. Cosmid end probes used for orientation of the cosmid contig are indicated as an open (C-for) or closed triangle (A-rev). (B) DNA fragments used for complementation experiments. The open bars represent the cosmid clones G and L. Shaded bars indicate different DNA fragments of cosmid G used for complementation. The position of the ET1 cDNA is displayed as a shaded box.

Figure 2

Functional complementation of ls¹. Comparison of phenotypes of Antimold B (A, D, and G), Antimold B-ls¹ (B, E, and H), and Antimold B-ls¹ transformed with cosmid G (C, F, and I). The pictures show the growth habit (A-C), a close up of leaf axils (D-F), and a close-up of a flower (G-I).

Figure 3

Sequence analysis of the Ls gene. Alignment of the amino acid sequences of the Ls protein with the Arabidopsis thaliana proteins SCR (19), RGA (21), and GAI (20). Identical residues are displayed in reverse type and similar residues are in gray boxes. The VHIID domain is underlined, the leucine residues defining the conserved leucine heptad repeat are identified by asterisks, and the LXXLL motif by triangles.

Figure 4

RT-PCR detection of Ls mRNA in different plant organs. (A) Total RNA from different plant organs was analyzed by RT-PCR, and the PCR products were hybridized to the Ls cDNA as probe. Amplification of actin cDNA was used to ensure that equal amounts of cDNA were added to each PCR reaction. (B) Total RNA was extracted from leaves of plants homozygous for Antimold B-Ls (Wt), Antimold B-ls¹, and Primabel-ls² and then analyzed by RT-PCR.