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Abstract

Although photoreceptors are expressed throughout all plant organs, most studies
have focused on their function in aerial parts with laboratory‐grown plants. Photoreceptor
function in naturally dark‐grown roots of plants in their native habitats is lacking.
We characterized patterns of photoreceptor expression in field‐ and glasshousegrown
Nicotiana attenuata plants, silenced the expression of PhyB1/B2/A/Cry2 whose
root transcripts levels were greater/equal to those of shoots, and by micrografting
combined empty vector transformed shoots onto photoreceptor‐silenced roots, creating
chimeric plants with “blind” roots but “sighted” shoots. Micrografting procedure
was robust in both field and glasshouse, as demonstrated by transcript accumulation
patterns, and a spatially‐explicit lignin visual reporter chimeric line. Field‐ and glasshouse‐
grown plants with PhyB1B2, but not PhyA or Cry2, ‐blind roots, were delayed
in stalk elongation compared with control plants, robustly for two field seasons.
Wild‐type plants with roots directly exposed to FR phenocopied the growth of
irPhyB1B2‐blind root grafts. Additionally, root‐expressed PhyB1B2 was required to
activate the positive photomorphogenic regulator, HY5, in response to aboveground
light. We conclude that roots of plants growing deep into the soil in nature sense
aboveground light, and possibly soil temperature, via PhyB1B2 to control key traits, such as stalk elongation.