Loss of function of the HSFA9 seed longevity program

Abstract

Gain of function approaches that have been published by our laboratory determined that HSFA9 (Heat Shock Factor A9) activates a genetic program contributing to seed longevity and to desiccation tolerance in plant embryos. We now evaluate the role(s) of HSFA9 by loss of function using different modified forms of HaHSFA9 (sunflower HSFA9), which were specifically overexpressed in seeds of transgenic tobacco. We used two inactive forms (M1, M2) with deletion or mutation of the transcription activation domain of HaHSFA9, and a third form (M3) with HaHSFA9 converted to a potent active repressor by fusion of the SRDX motif. The three forms showed similar protein accumulation in transgenic seeds; however, only HaHSFA9-SRDX showed a highly significant reduction of seed longevity, as determined by controlled deterioration tests, a rapid seed ageing procedure. HaHSFA9-SRDX impaired the genetic program controlled by the tobacco HSFA9, with a drastic reduction in the accumulation of seed heat shock proteins (HSPs) including seed-specific small HSP (sHSP) belonging to cytosolic (CI, CII) classes. Despite such effects, the HaHSFA9-SRDX seeds could survive developmental desiccation during embryogenesis and their subsequent germination was not reduced. We infer that the HSFA9 genetic program contributes only partially to seed-desiccation tolerance and longevity.

ARABIDOPSIS THALIANA HOMEOBOX25 Uncovers a Role for Gibberellins in Seed Longevity

“…days instead of years, as in natural aging; Woodstock and Taylorson, 1981;Tesnier et al, 2002;Prieto-Dapena et al, 2006;Tejedor-Cano et al, 2010). Accelerated aging mimics natural aging (Tesnier et al, 2002;, and similar results are obtained with controlled hydration or with seeds imbibed in water (Tejedor-Cano et al, 2010). Our aging procedure with imbibed seeds incubated at 42°C for 1 to 2 d has been validated by the observed correlation between tolerance to natural aging and to accelerated aging in four different mutants obtained in our screening (Fig.…”

“…Seeds are partially or completely rehydrated and exposed to high temperatures, leading to rapid loss of seed viability (e.g. days instead of years, as in natural aging; Woodstock and Taylorson, 1981;Tesnier et al, 2002;Prieto-Dapena et al, 2006;Tejedor-Cano et al, 2010). Accelerated aging mimics natural aging (Tesnier et al, 2002;, and similar results are obtained with controlled hydration or with seeds imbibed in water (Tejedor-Cano et al, 2010).…”

“…This procedure was a modification of the "basal thermotolerance assay" of Tejedor-Cano et al (2010). Seeds were imbibed in water, stratified for 2 d at 4°C, and incubated at 42°C for 1 to 2 d (relative humidity of 100%).…”

“…Also, all mutants previously described were obtained from known genes of stress defenses or involved in seed development. We have screened an "activation-tagging" mutant collection of Arabidopsis (Weigel et al, 2000), selecting for tolerance of seeds to natural and accelerated aging (Tesnier et al, 2002;Tejedor-Cano et al, 2010). As a first result, we report that the transcription factor ARABIDOPSIS THALIANA HOMEOBOX25/ZINC FINGER HOMEODOMAIN2/ ZINC FINGER HOMEODOMAIN1 (ATHB25/ZFHD2/ ZHD1; At5g65410) is an important determinant of seed longevity by positively regulating the GIBBERELLIC ACID3-OXIDASE2 (GA3OX2) gene and, therefore, GA biosynthesis.…”

Repression by an auxin/indole acetic acid protein connects auxin signaling with heat shock factor-mediated seed longevity

“…In Arabidopsis, transcription of the HSFA9 gene is activated by ABA-insensitive 3 (ABI3), a key regulator controlling late-seed development (2). Target genes of HSFA9 encode different heat shock proteins (HSP) (1)(2)(3)(4)(5). Gain of function (3,4) and loss of function (5) approaches determined that in sunflower (Helianthus annuus L.) and tobacco (Nicotiana tabacum L.), HSFA9 activate transcription of specific small heat-shock protein (shsp) genes.…”