Kalilo plasmids are a family of four distinct members with individual global distributions across species

Kalilo is a linear 9-kb plasmid, isolated originally from Hawaiian strains of the heterothallic fungus Neurospora intermedia. Its properties include t erminal inverted repeats, two ORFs coding for a presumptive DNA and an RNA polymerase, and the ability to cause senescence in its original host and in the closely related species Neurospora crassa. We have examined natural is olates alleged to contain plasmids homologous to kalilo. Most of these isol ates do in fact contain plasmids with so close an identity to kalilo as to be certain relatives. We found a new case of kalilo in Neurospora tetrasper ma from Moorea-Tahiti, and a new case of LA-kalilo (previously found only i n N. tetrasperma) in N. crassa from Haiti. A previously unreported, substan tially shorter, kalilo variant has been found in three geographically separ ate isolates of the heterothallic species Neurospora discreta. Therefore, i f the previously reported kalilo variant from the genus Gelasinospora is in cluded, in all there are four members of the kalilo plasmid family. The mai n differences between these plasmids are in the terminal inverted repeats ( TIRs). The phylogeny of the TIR sequences is largely congruent with that of nuclear DNA in the species in which they are found, suggesting that the pl asmids are related by vertical descent throughout the evolution of these sp ecies. However, there are two cases of a plasmid found in a heterothallic a nd a pseudohomothallic species in the same global area; these cases might h ave arisen from more recent horizontal transmission or introgression.