Transactions of the Illinois State Academy of Science received 8/18/97 (1998), Volume 91, 1 and 2, pp.1-11 accepted 10/30/97 The Intron in Chloroplast Gene rpl 16 is Missing From the Flowering Plant Families Geraniaceae, Goodeniaceae, and Plumbaginaceae. Mary L. Campagna and Stephen R. Downie Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801 ABSTRACT Previous studies have shown that in the vast majority of land plants examined to date, the chloroplast gene rpl16 is interrupted by an intron (of about 1 kilobase in size in most angiosperms), but that in Limonium gmelinii (Plumbaginaceae) and Geraniaceae sensu stricto the intron has been lost. In order to uncover other instances of intron loss, the complete rpl16 intron and flanking DNA regions from over 210 species, representing 86 families of angiosperms, were amplified using the polymerase chain reaction (PCR) technique. We report the widespread distribution of the rpl16 intron in angiosperm chloroplast DNAs, and confirm that the intron is missing from the chloroplast genomes of Erodium chamaedryoides and Pelargonium * hortorum (the only two species of Geraniaceae included in our investigation), and from three of the four examined genera of Plumbaginaceae (Armeria, Goniolimon, and Limonium, but not Plumbago). Furthermore, we report that the intron is missing from Goodenia ovata and Scaevola sericea, the only representatives examined from the family Goodeniaceae. DNA sequencing of the rpl16 intron region in representatives of the seven genera lacking the intron confirms its absence and shows that the intron has been precisely removed from the gene along established exon/intron splice sites. Based upon available phylogenetic information and distribution of intron loss, we conclude that this rare genomic structural mutation has occurred independently at least three times during the evolution of flowering plants. INTRODUCTION The chloroplast gene rpl16, encoding the ribosomal protein L16, is interrupted by an intron in many, but not all, land plants. DNA sequencing has revealed that this intron is present in plants spanning diverse evolutionary lineages, such as in the liverwort Marchantia polymorpha (Ohyama et al., 1986), the gymnosperm black pine (Pinus thunbergii; Wakasugi et al., 1994), the dicot tobacco (Nicotiana tabacum; Shinozaki et al., 1986), and the monocots duckweed (Spirodela oligorhiza; Posno et al., 1986; Jordan et al., 1996) and corn (Zea mays; McLaughlin and Larrinua, 1987). Among these species, the intron varies considerably in length, from 536 base pairs (bp) in Marchantia to 1,411 bp in duckweed. In most angiosperms, the intron is about 1 kb (kilobase) in