Abstract
SummaryStomata are pores found on the surfaces of leaves, and they regulate gas exchange between the plant and the environment [1]. Stomatal development is highly plastic and is influenced by environmental signals [2]. Light stimulates stomatal development, and this response is mediated by plant photoreceptors [3–5], with the red-light photoreceptor phytochrome B (phyB) having a dominant role in white light [3]. Light also regulates stomatal development systemically, with the irradiance perceived by mature leaves modulating stomatal development in young leaves [6, 7]. Here, we show that phyB is required for this systemic response. Using a combination of tissue-specific expression and an inducible expression system in the loss-of-function phyB-9 mutant [8], we show that phyB expression in the stomatal lineage, mesophyll, and phloem is sufficient to restore wild-type stomatal development. Induction of PHYB in mature leaves also rescues stomatal development in young untreated leaves, whereas phyB mutants are defective in the systemic regulation of stomatal development. Our data show that phyB acts systemically to regulate cell fate decisions in the leaf epidermis.
Highlights
This involves changes in epidermal cell fate that result in alterations to the stomatal index (SI; the ratio of the number of stomata in a given area divided by the total number of stomata and other epidermal cells in that area) and changes in stomatal density (SD)
White light, with phytochrome B (phyB) mutants having reduced SI at higher photon irradiances [3, 4]. phyB is expressed widely throughout the life cycle of Arabidopsis and throughout the leaf, including in early stomatal lineage cells, guard cells, and pavement cells [5, 14]. This would suggest that phyB can act cell autonomously to regulate phyB-dependent responses, mesophyll-specific expression was found to be sufficient to suppress flowering, indicating that some phyB responses are regulated non-cell autonomously [15]
Constructs were stably introduced into the phyB-9 mutant (Col-0 background) by Agrobacterium tumefaciens-mediated transformation, and two independent transformed lines were analyzed per promoter construct and gave similar expression patterns
Summary
Stomata are pores found on the surfaces of leaves, and they regulate gas exchange between the plant and the environment [1]. This response is mediated by plant photoreceptors [3,4,5], with the red-light photoreceptor phytochrome B (phyB) having a dominant role in white light [3]. Light regulates stomatal development systemically, with the irradiance perceived by mature leaves modulating stomatal development in young leaves [6, 7]. Using a combination of tissue-specific expression and an inducible expression system in the loss-of-function phyB-9 mutant [8], we show that phyB expression in the stomatal lineage, mesophyll, and phloem is sufficient to restore wild-type stomatal development. Induction of PHYB in mature leaves rescues stomatal development in young untreated leaves, whereas phyB mutants are defective in the systemic regulation of stomatal development. Our data show that phyB acts systemically to regulate cell fate decisions in the leaf epidermis
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