Complete sequences of the plastic1 gene mcrtK \+-eredetermined for 62 species of Poaceae from 6 0 genera. 2 6 tribes. and nine iul~fanliliesto infer phylogenetic relatiollsllips. Rrsfio tetr-upli~llus(Restionaceae) ant1 .loinl illea ascendens (Joi~l\illeacrae) were used as outgroups. Clatlistic. analysis using PAUP)ieltletl 3 9 most parsimo~lioustrees \+-it11several well-supl~orteclmajor lineages. Tlle strict conse~lsusLree she\+-s S~reptocl~cre~a and 4~iomochlocrforming the two most basal lineages in grasses. follo~+-ecl 11) I'licrl-us 11eing sister to the remaining species. The other grasses divide into three clades: (1) sul~fanlil) Banll~~~soitleae (exclucli~lgRrcrchje!,~r7c~ii) plus Pooideae: (2) Oryzoicleae: and (3) s~ll~fanlilies Panicoideae. Ar~lntli~loitleae. monopllyly Cento~hecoideae.ancl Chloridoideae (termed PACC). EacepL for A~~~~~~c l i n o i c l e a e. of each P.1CC subfamily is generally well supported; h o~\ e \ e n relationships among subfamilies are unresolved or weakly supportetl. Results ol~tai~lecl using 117crtK sequences are largely consistent wit11 other phylogenies l~asecl on molecular ancl s~ructural data. particularly in that relationsllips among subfamilies remain ~~n c l e a r. We h a n k Nigel Barker. Lynn Clark. Travis Columbus. Jerr! Davis. Tarciso Filgueiras. Gal? Fleming, Surrey Jac.ol)s. Davicl Kneppet A. Nishiwaki. John Randall, Thomas W'iebolclt, the Botallical Garden at Bo~ill.ant1 the hlissouri Botanical Garden for supplying DNA or plant samples. Seecl material for some accessions was kindl) provided 11) the

Although the matK gene has been used in addressing systematic questions in four families, its potential application to plant systematics above the family level has not been investigated. This paper examines the rates, patterns, and types of nucleotide substitutions in the gene and addresses its utility in constructing phylogenies above the family level. Eleven complete sequences from the GenBank representing seed plants and liverworts and nine partial sequences generated for genera representing the monocot families Poaceae, Joinvilleaceae, Cyperaceae, and Smilacaceae were analyzed. The study underscored the high rate of substitution in the gene and the presence of mutationally conserved sectors. The use of different sectors of the gene and the cumulative inclusion of informative sites showed that the 3' region was most useful in resolving phylogeny, and that the topology and robustness of the tree reached a plateau after the inclusion of 100 informative sites from that region for the taxa used. The impact of using partial sequencing on sample size is addressed. The presence of a relatively conserved 3' region and the less conserved 5' region provides two sets of characters that can be used at different taxonomic levels from the tribal to the division levels.

Mounting evidence suggests that terrestrialization of plants started in streptophyte green algae, favoured by their dual existence in freshwater and subaerial/terrestrial environments. Here, we present the genomes of Mesostigma viride and Chlorokybus atmophyticus, two sister taxa in the earliest-diverging clade of streptophyte algae dwelling in freshwater and subaerial/terrestrial environments, respectively. We provide evidence that the common ancestor of M. viride and C. atmophyticus (and thus of streptophytes) had already developed traits associated with a subaerial/terrestrial environment, such as embryophyte-type photorespiration, canonical plant phytochrome, several phytohormones and transcription factors involved in responses to environmental stresses, and evolution of cellulose synthase and cellulose synthase-like genes characteristic of embryophytes. Both genomes differed markedly in genome size and structure, and in gene family composition, revealing their dynamic nature, presumably in response to adaptations to their contrasting environments. The ancestor of M. viride possibly lost several genomic traits associated with a subaerial/terrestrial environment following transition to a freshwater habitat.

Genome analysis of the pico-eukaryotic marine green alga Prasinoderma coloniale CCMP 1413 unveils the existence of a novel phylum within green plants (Viridiplantae), the Prasinodermophyta, which diverged before the split of Chlorophyta and Streptophyta. Structural features of the genome and gene family comparisons revealed an intermediate position of the P. coloniale genome (25.3 Mb) between the extremely compact, small genomes of picoplanktonic Mamiellophyceae (Chlorophyta) and the larger, more complex genomes of early-diverging streptophyte algae. Reconstruction of the minimal core genome of Viridiplantae allowed identification of an ancestral toolkit of transcription factors and flagellar proteins. Adaptations of P. coloniale to its deep-water, oligotrophic environment involved expansion of light-harvesting proteins, reduction of early light-induced proteins, evolution of a distinct type of C 4 photosynthesis and carbon-concentrating mechanism, synthesis of the metal-complexing metabolite picolinic acid, and vitamin B 1 , B 7 and B 12 auxotrophy. The P. coloniale genome provides first insights into the dawn of green plant evolution.