Study species
Chionochloa pallens (midribbed snow tussock) is an endemic
alpine New Zealand perennial grass. 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 grows for four to five years in the field
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 dying. 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. pallens vary 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 (Kelly et al., 2013;
Samarth et al., 2020).