A quiescent-like strategy underlies extreme stress tolerance and clonal offset maintenance during drought in Sempervivum tectorum

Aerobic organisms are prone to oxidative stress when meeting their metabolic and developmental demands, particularly under stressful environments. Here, we aimed to elucidate survival strategies to withstand an extreme drought stress in a clonal plant species at various organizational levels, including parental and offset rosettes. We explored physiological and morphological mechanisms underlying stress tolerance and offset maintenance in the tolerant plant species houseleek (Sempervivum tectorum) under controlled conditions—where potted plants were exposed to complete water withdrawal for up to seven months—and natural habitat conditions. We found an unexpected quiescent-like strategy through the maintenance of low oxidative levels in the leaves under severe stress. Moreover, S. tectorum plants employed a morphological strategy driven by the spatiotemporal senescence pattern along the rosette, thus protecting the apical inner bud under stress. Even with very low resource availability, the parent plant and the associated offspring adjusted their physiology, keeping the stolon-connected offsets alive for as long as required until rooting into the soil (sometimes for several months), without compromising the parental rosette. The quiescent response in the parental rosette is maintained despite an increasing number of unrooted offsets due to photoprotective and morphological adjustments in leaves, with higher endogenous ABA levels. These results revealed the mechanisms through which this species extended its survival during prolonged periods of drought stress without irreversible physiological costs of clonal reproduction for the whole genet.