Premium
The velamen protects photosynthetic orchid roots against UV ‐ B damage, and a large dated phylogeny implies multiple gains and losses of this function during the C enozoic
Author(s) -
Chomicki Guillaume,
Bidel Luc P. R.,
Ming Feng,
Coiro Mario,
Zhang Xuan,
Wang Yaofeng,
Baissac Yves,
JayAllemand Christian,
Renner Susanne S.
Publication year - 2015
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.13106
Subject(s) - epiphyte , biology , botany , photosynthesis , phylogenetics , phylogenetic tree , chalcone synthase , gene , genetics , gene expression
SummaryUV ‐ B radiation damage in leaves is prevented by epidermal UV ‐screening compounds that can be modulated throughout ontogeny. In epiphytic orchids, roots need to be protected against UV ‐ B because they photosynthesize, sometimes even replacing the leaves. How orchid roots, which are covered by a dead tissue called velamen, avoid UV ‐ B radiation is currently unknown. We tested for a UV ‐ B protective function of the velamen using gene expression analyses, mass spectrometry, histochemistry, and chlorophyll fluorescence in P halaenopsis × hybrida roots. We also investigated its evolution using comparative phylogenetic methods. Our data show that two paralogues of the chalcone synthase ( CHS ) gene family are UV ‐ B ‐induced in orchid root tips, triggering the accumulation of two UV ‐ B ‐absorbing flavonoids and resulting in effective protection of the photosynthetic root cortex. Phylogenetic and dating analyses imply that the two CHS lineages duplicated c . 100 million yr before the rise of epiphytic orchids. These findings indicate an additional role for the epiphytic orchid velamen previously thought to function solely in absorbing water and nutrients. This new function, which fundamentally differs from the mechanism of UV ‐ B avoidance in leaves, arose following an ancient duplication of CHS , and has probably contributed to the family's expansion into the canopy during the Cenozoic.