NCEDs drive Rising but not Peaking abscisic acid profiles in diverging conifer species

Climate change poses one of the greatest threats to forest ecosystem integrity. An improved understanding of how trees respond to extreme climatic events is crucial to find new ways of managing forests in the face of global warming. In this work we look at the genetic mechanisms governing the production of the plant hormone abscisic acid (ABA), which safeguards plant’s water status by the means of two divergent modes across different conifer species. We find that conifers from evolutionary ancient families adopt a conservative water strategy during drought by accumulating high levels of ABA in their leaves, which we describe as Rising types, while more derived species accumulate the hormone in a transient manner and allow for greater water loss, accordingly to a Peaking type. Moreover, we provide evidence that these contrasting strategies may be controlled by divergent gene expression, including sequences involved in the biosynthetic and catabolic pathways of ABA, and especially nine- cis -epoxycarotenoid dioxygenases ( NCEDs ). Our results help to clarify the genetic and physiological bases of iso/anisohydric responses. We believe that studying these and other related genes that regulate plant water status, such as those involved in ABA storage and mobilisation, may help foresters develop and grow more resistant trees.