ARABIDOPSIS THALIANA HOMEOBOX25 Uncovers a Role for Gibberellins in Seed Longevity

Abstract

Seed longevity is crucial for agriculture and plant genetic diversity, but it is limited by cellular damage during storage. Seeds are protected against aging by cellular defenses and by structures such as the seed coat. We have screened an activation-tagging mutant collection of Arabidopsis (Arabidopsis thaliana) and selected four dominant mutants with improved seed longevity (isl1-1D to isl4-1D) under both natural and accelerated aging conditions. In the isl1-1D mutant, characterized in this work, overexpression of the transcription factor ARABIDOPSIS THALIANA HOMEOBOX25 (ATHB25; At5g65410) increases the expression of GIBBERELLIC ACID3-OXIDASE2, encoding a gibberellin (GA) biosynthetic enzyme, and the levels of GA 1 and GA 4 are higher (3.2-and 1.4-fold, respectively) in the mutant than in the wild type. The morphological and seed longevity phenotypes of the athb25-1D mutant were recapitulated in transgenic plants with moderate (4-to 6-fold) overexpression of ATHB25. Simultaneous knockdown of ATHB25, ATHB22, and ATHB31 expression decreases seed longevity, as does loss of ATHB25 and ATHB22 function in a double mutant line. Seeds from wild-type plants treated with GA and from a quintuple DELLA mutant (with constitutive GA signaling) are more tolerant to aging, providing additional evidence for a role of GA in seed longevity. A correlation was observed in several genotypes between seed longevity and mucilage formation at the seed surface, suggesting that GA may act by reinforcing the seed coat. This mechanism was supported by the observation of a maternal effect in reciprocal crosses between the wild type and the athb25-1D mutant.

PRX2 and PRX25, peroxidases regulated by COG1, are involved in seed longevity in Arabidopsis

“…During the last years, we have been trying to define the molecular mechanism underpinning COG1 and ATHB25‐mediated resistance to seed aging. Overexpression of these TFs produces seeds with an increase in the accumulation of suberin in the PL layer of the seed coat, likely reducing the embryo oxidation and extending seed viability (Bueso et al, ; Bueso et al, ). The specific target genes and processes involved in mediating this reinforcement of the seed coat is the next issue to clarify.…”

A role for auxin signaling in the acquisition of longevity during seed maturation

“…These regulators form an elaborate network that is necessary for the expression of LEA proteins and HSPs, the accumulation of raffinose family oligosaccharides (RFOs),Chl breakdown and chloroplast dismantling during late maturation (Sugliani et al, 2009;Dekkers et al, 2016;Zinsmeister et al, 2016;Leprince et al, 2017). A second hormone involved in longevity is GA (Bueso et al, 2014). Mutants of the transcription factor HOMEOBOX25 (ATHB25) are more sensitive to accelerated deterioration.…”

RNA Sequencing of Contaminated Seeds Reveals the State of the Seed Permissive for Pre-Harvest Aflatoxin Contamination and Points to a Potential Susceptibility Factor

“…In aflatoxin contaminated seeds, the GA pathway has been down-regulated (Figure 7). Gibberellic acid has been shown to promote seed coat development [42]. In these data, the mucilage metabolic process involved in seed coat development is also down-regulated in aflatoxin contaminated seeds, suggesting a possible seed coat deficiency in contaminated seeds compared to seeds that have escaped contamination.…”