Plants have evolved annual and perennial life forms as alternative strategies to adapt reproduction and survival to environmental constraints. In isolated situations, such as islands, woody perennials have evolved repeatedly from annual ancestors 1 . Although the molecular basis of the rapid evolution of insular woodiness is unknown, the molecular difference between perennials and annuals might be rather small, and a change between these life strategies might not require major genetic innovations 2,3 . Developmental regulators can strongly affect evolutionary variation 4 and genes involved in meristem transitions are good candidates for a switch in growth habit. We found that the MADS box proteins SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FRUITFULL (FUL) not only control flowering time, but also affect determinacy of all meristems. In addition, downregulation of both proteins established phenotypes common to the lifestyle of perennial plants, suggesting their involvement in the prevention of secondary growth and longevity in annual life forms.Plant growth originates from a small number of undifferentiated cells called meristems. Primary meristems are established during embryogenesis and form primary tissues from which all plant organs develop. Secondary meristems, such as axillary meristems and the cambium, originate within primary tissues. Meristems can be determinate-that is, consumed for the formation of an organ-or indeterminate, meaning that they are active throughout the life span of a plant. Upon floral induction in annual plants, vegetative shoot meristems undergo the transition to inflorescence meristems. These inflorescence meristems will remain indeterminate for some time to generate determinate floral meristems giving rise to flowers. Finally, all meristems are consumed and the plants die in the same growing season. In contrast, perennial plants have evolved more elaborate life strategies to survive harsh environmental conditions for many years by forming perennial structures such as overwintering buds, bulbs or tubers, which contain at least one indeterminate meristem for the outgrowth in the next season 2 . Often, perennial plants incorporate enormous amounts of long-lived and eventually dead biomass (wood) through cambial activity (secondary growth).Arabidopsis thaliana is a small annual herb in which floral induction is controlled by different flowering-time pathways. These pathways depend on environmental cues, such as day length (photoperiod) and vernalization (cold temperature), or on plant age. Arabidopsis is a facultative long-day plant that flowers much faster under long (16 h/day) than short (8 h/day) light periods. After perceiving flowering-inducing long days, the key regulator of the photoperiodic pathway, CONSTANS (CO), activates FT (FLOWERING LOCUS T) in the leaf vasculature. The FT protein is transported to apical meristems, where it triggers the floral transition 5 . SOC1 (AGL20) and FUL (AGL8) are MADS box genes acting downstream of FT in apical meristems, but they are ...

Summary• This study describes the quantitative trait locus (QTL) analysis of cadmium (Cd), zinc (Zn), iron (Fe), potassium (K), magnesium (Mg) and calcium (Ca) accumulation in the pseudometallophyte Arabidopsis halleri under conditions of Cd excess using an interspecific A. halleri · Arabidopsis lyrata F 2 population.• Our data provide evidence for the implication of one major QTL in Cd hyperaccumulation in A. halleri, and suggests that Cd tolerance and accumulation are not independent in A. halleri. Moreover, the major loci responsible for Zn hyperaccumulation in the absence of Cd appear to be the same when Cd is present at high concentrations.• More than twofold higher Fe concentrations were measured in A. halleri shoots than in A. lyrata, suggesting a different regulation of Fe accumulation in the hyperaccumulator.• With the exception of Ca, the accumulation of Cd was significantly correlated with the accumulation of all elements measured in the F 2 progeny, suggesting pleiotropic gene action. However, QTL analysis identified pleiotropic QTLs only for Cd, Zn and Fe. Mg accumulation was negatively correlated with Cd accumulation, as well as with dry shoot biomass, suggesting that it might indicate cellular damage.

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The genus Nicotiana contains species and varieties that respond differently to photoperiod for flowering time control as day-neutral, short-day and long-day plants. In classical photoperiodism studies, these varieties have been widely used to analyse the physiological nature for floral induction by day length. Since key regulators for flowering time control by day length have been identified in Arabidopsis thaliana by molecular genetic studies, it was intriguing to analyse how closely related plants in the Nicotiana genus with opposite photoperiodic requirements respond to certain flowering time regulators. SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FRUITFULL (FUL) are two MADS box genes that are involved in the regulation of flowering time in Arabidopsis. SOC1 is a central flowering time pathway integrator, whereas the exact role of FUL for floral induction has not been established yet. The putative Nicotiana orthologs of SOC1 and FUL, NtSOC1 and NtFUL, were studied in day-neutral tobacco Nicotiana tabacum cv Hicks, in short-day tobacco N. tabacum cv Hicks Maryland Mammoth (MM) and long-day N. sylvestris plants. Both genes were similarly expressed under short- and long-day conditions in day-neutral and short-day tobaccos, but showed a different expression pattern in N. sylvestris. Overexpression of NtSOC1 and NtFUL caused flowering either in strict short-day (NtSOC1) or long-day (NtFUL) Nicotiana varieties under non-inductive photoperiods, indicating that these genes might be limiting for floral induction under non-inductive conditions in different Nicotiana varieties.