Abstract
Heat Stress Factor A9 (A9), a seed-specific transcription factor contributing to seed longevity, also enhances phytochrome-dependent seedling greening. The RNA-seq analyses of imbibed-seed transcripts here reported indicated potential additional effects of A9 on cryptochrome-mediated blue-light responses. These analyses also suggested that in contrast to the A9 effects on longevity, which require coactivation by additional factors as A4a, A9 alone might suffice for the enhancement of photomorphogenesis at the seedling stage. We found that upon its seed-specific overexpression, A9 indeed enhanced the expected blue-light responses. Comparative loss-of-function analyses of longevity and greening, performed by similar expression of dominant-negative and inactive forms of A9, not only confirmed the additional greening effects of A9, but also were consistent with A9 not requiring A4a (or additional factors) for the greening effects. Our results strongly indicate that A9 would differentially regulate seed longevity and photomorphogenesis at the seedling stage, A9 alone sufficing for both the phytochrome- and cryptochrome-dependent greening enhancement effects.
Highlights
In plants, the heat-shock response and some crucial developmental processes are regulated by a gene family of transcription factors known as the heat-shock transcription factors (HSFs)
Our results strongly indicate that A9 would differentially regulate seed longevity and photomorphogenesis at the seedling stage, A9 alone sufficing for both the phytochrome- and cryptochrome-dependent greening enhancement effects
To investigate whether the regulation by A9 is similar or different in both cases, we first analyzed the effect of A4a on transient transcriptional activation of the Phytochrome A (PHYA) promoter, a photoreceptor that is directly activated by A9 [17]
Summary
The heat-shock response and some crucial developmental processes are regulated by a gene family of transcription factors known as the heat-shock transcription factors (HSFs). The functional specialization of the multiple plant HSFs is, for the most part, unexplored. HSFs from a few plant species have been functionally analyzed [1,2]. Our lab has characterized HSFs, which, in sunflower (Helianthus annuus L.), contribute to longevity, thermotolerance, and desiccation tolerance of seeds. HaHSFA9 (A9; Helianthus annuus Heat Stress Factor A9) is a peculiar Class A HSF that, in sunflower, is expressed only in seeds [3]. The gaining of function upon the overexpression of A9 in transgenic tobacco has indicated its involvement in thermotolerance, seed longevity, and tolerance to extreme desiccation [4,5]. The photosynthetic apparatus and green organs of 35S:A9 seedlings (constitutively overexpressing A9) showed an unusual resistance to extreme conditions of dehydration and oxidative stress [6]
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