Study species
Chionochloa pallens (midribbed snow tussock) is an endemic
alpine New Zealand perennial, in the Danthonioideae sub-family of the
Poaceae (grasses) (Soreng et al., 2015). Plants grow as tussocks
(bunchgrasses) around 0.5-1.5 m tall and 15-50 cm in basal diameter.
These are very long-lived plants (> 100 years) with
discrete individuals. Each individual plant typically comprises hundreds
of tillers, each of which in the field is reported to grow for four to
five years prior to attaining reproductive maturity (Mark, 1965; Rees et
al., 2002). Tillers may then wait some years before switching from
vegetative to reproductive, producing a flower stalk (or culm) and
typically at least one daughter tiller, before that flowering tiller
(but not the rest of the plant) dies. Activation of the inflorescence
and floral development in C. pallens occurs a year before
flowering (Mark, 1965, and see Appendix S1 in the supplementary
information), so we sampled leaves for genetic analysis from marked
tillers and stored the samples at -80 °C until the fate of that tiller
could be determined up to a year later. Informative samples were then
selected for RNA analysis. The levels of flowering in C. pallensvary markedly between years (Kelly et al., 2013; Kelly et al., 2000).
Previous studies, including transplant experiments to different
altitudes, have shown that flowering in Chionochloa is heavier
after warm summer temperatures in the year preceding flowering (Mark,
1965; Kelly et al., 2013).