Leaves are determinate organs that arise from the flanks of the shoot apical meristem as polar structures with distinct adaxial (dorsal) and abaxial (ventral) sides. Opposing regulatory interactions between genes specifying adaxial or abaxial fates function to maintain dorsoventral polarity. One component of this regulatory network is the Myb-domain transcription factor gene ASYMMETRIC LEAVES1 (AS1). The contribution of AS1 to leaf polarity varies across different plant species; however, in Arabidopsis, as1 mutants have only mild defects in leaf polarity, suggesting that alternate pathways exist for leaf patterning. Here, we describe three genes, PIGGYBACK1 (PGY1), PGY2 and PGY3, which alter leaf patterning in the absence of AS1. All three pgy mutants develop dramatic ectopic lamina outgrowths on the adaxial side of the leaf in an as1 mutant background. This leaf-patterning defect is enhanced by mutations in the adaxial HD-ZIPIII gene REVOLUTA (REV), and is suppressed by mutations in abaxial KANADI genes. Thus, PGY genes influence leaf development via genetic interactions with the HD-ZIPIII-KANADI pathway. PGY1, PGY2 and PGY3 encode cytoplasmic large subunit ribosomal proteins, L10a, L9 and L5, respectively. Our results suggest a role for translation in leaf dorsoventral patterning and indicate that ribosomes are regulators of key patterning events in plant development. Development 135, 1315Development 135, -1324Development 135, (2008 DEVELOPMENT 1316 from the Arabidopsis Biological Resource Centre (ABRC). kan1-2 and kan2-1 were obtained from John Bowman. All genetic interactions were in a Ler background. Plants were grown either in soil or on Murashige and Skoog media at 22°C with a day length of 16 hours.
KEY WORDS: Ribosomal protein, Leaf polarity, ASYMMETRIC LEAVES1, PIGGYBACK, Arabidopsis
Geneticspgy genes were cloned using Ler ϫ Columbia F2 mapping populations. For complementation a 2.1 kb genomic fragment encompassing At2g27530, a 5 kb genomic fragment encompassing At1g33140 and a 3.5 kb genomic fragment encompassing At3g25520 were cloned into the binary vector pMDC123 (Curtis and Grossniklaus, 2003) and transformed into pgy1-1/pgy1-1 as1/+, pgy2-1/pgy2-1 as1/+ and pgy3-1/pgy3-1 as1/+ plants, respectively, using standard agrobacterium-mediated transformation (Clough and Bent, 1998). For each complementation construct, basta resistant plants with an as1 phenotype were confirmed as as1 pgy homozygotes.as1-1 rev-6 was analysed in the F3 generation of the cross as1-1 ϫ rev-6. In the F2 generation of this cross as1-1 rev-6 segregated at 1:15. pgy1-1 rev-6 were obtained from the F3 generation of the cross pgy1-1 ϫ rev-6. Progeny from pgy1-1 rev-6/+ individuals segregated 1:3 pgy1-1 rev-6 mutants. as1-1 pgy1-1 rev-6 triple mutants were analysed in the F4 generation of the cross as1-1 pgy1-1 ϫ as1-1 rev-6, after selfing as1-1 pgy1-1 rev-6/+ F3 plants. Segregation of as1-1 pgy1-1 rev-6 in this F4 generation was 1:3. as1-1 kan1-2 and pgy1-1 kan1-2 were obtained from the F3 generation of the respective crosses...