DEVELOPMENTAL REGULATION OF RIBOSOMAL-PROTEIN L16 GENES IN ARABIDOPSIS-THALIANA

Lateral roots can be synchronously induced in Arabidopsis by a brief a uxin treatment. An early event in the development of a lateral root pr imordium is the accumulation of mRNAs encoding ribosomal proteins. In site hybridizations show that mRNA encoding one ribosomal protein, L16 , accumulates in all rapidly proliferating tissues including the shoot and root apical meristems and lateral root primordia. To understand f urther the mechanisms by which ribosomal proteins are coordinately syn thesized, two genes encoding the ribosomal protein L16 were isolated f rom Arabidopsis thaliana. Promoter sequences from each RPL16A and RPL1 6B were fused to the beta-glucuronidase reporter gene GUS. The promote r of RPL16B (from -848 to -19) conferred X-Gluc staining in proliferat ing tissues including the shoot and root apical meristems. When GUS wa s expressed from the RPL16A promoter (from -875 to -22), X-Gluc staini ng was observed in cells in the root stele and in anthers. When seedli ngs transformed with either promoter construct were treated with auxin to induce lateral roots, X-Gluc staining accumulated in the lateral r oot primordia by 16 h after induction. Transcription of the RPL 16B pr omoter appears to be correlated with cell division, while transcriptio n of the RPL16A promoter is very cell specific. Expression of two gene s encoding L16 during the early phase of lateral root initiation and i n developing pollen may serve to increase levels of ribosomal proteins during the rapid growth of these tissues.