The colonization of land by plants was a key event in the evolution of life. Here we report the draft genome sequence of the filamentous terrestrial alga Klebsormidium flaccidum (Division Charophyta, Order Klebsormidiales) to elucidate the early transition step from aquatic algae to land plants. Comparison of the genome sequence with that of other algae and land plants demonstrate that K. flaccidum acquired many genes specific to land plants. We demonstrate that K. flaccidum indeed produces several plant hormones and homologues of some of the signalling intermediates required for hormone actions in higher plants. The K. flaccidum genome also encodes a primitive system to protect against the harmful effects of high-intensity light. The presence of these plant-related systems in K. flaccidum suggests that, during evolution, this alga acquired the fundamental machinery required for adaptation to terrestrial environments.

In a wide variety of cells, various intracellular agents, such as Ca2+, ATP and cyclic nucleotides, regulate ionic conductances of the membrane. In cardiac cells, the intracellular Na+ concentration [( Na+]i) frequently increases when a disturbance occurs in the electrogenic Na-K pump activity or the Na-Ca exchange mechanism. We have investigated a possible role of [Na+]i in controlling ion channels by using a patch-clamp method, and have found a K+ channel that is gated by [Na+]i greater than 20 mM, but not by the intracellular Ca2+ concentration (approximately 10(-4) M). We report here that the channel has a unitary conductance of 207 +/- 19 pS (n = 16) with K+ concentrations of 150 mM outside and 49 mM inside, and shows no detectable voltage-dependent kinetics. The Na+-activated K+ channel represents a novel class of ionic channel.

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