Single-stranded DNA-binding protein that functions in both chloroplasts and nucleus. In chloroplasts, maintains plastid genome stability by preventing break-induced and short homology-dependent illegitimate recombinations. In nucleus, modulates telomere length homeostasis by inhibiting the action of the telomerase at the extreme termini of chromosomes. Is recruited to a distal element upstream of the kinesin KP1 to mediate the transcriptional repression of KP1. Is required for full salicylic acid-dependent plant disease resistance responses. Can bind double-stranded DNA in vivo. Homotetramer. Can localize to both chloroplast and nucleus (PubMed:15967440). By salicylic acid (SA) and infection by H.parasitica. No visible phenotype under normal growth conditions, but mutant plants present a progressive lengthening of telomeric repeats. Belongs to the Whirly family. It is uncertain whether Met-1 or Met-10 is the initiator.