LEA polypeptide profiling of recalcitrant and orthodox legume seeds reveals ABI3-regulated LEA protein abundance linked to desiccation tolerance

Abstract

In contrast to orthodox seeds that acquire desiccation tolerance during maturation, recalcitrant seeds are unable to survive drying. These desiccation-sensitive seeds constitute an interesting model for comparative analysis with phylogenetically close species that are desiccation tolerant. Considering the importance of LEA (late embryogenesis abundant) proteins as protective molecules both in drought and in desiccation tolerance, the heat-stable proteome was characterized in cotyledons of the legume Castanospermum australe and it was compared with that of the orthodox model legume Medicago truncatula. RNA sequencing identified transcripts of 16 homologues out of 17 LEA genes for which polypeptides are detected in M. truncatula seeds. It is shown that for 12 LEA genes, polypeptides were either absent or strongly reduced in C. australe cotyledons compared with M. truncatula seeds. Instead, osmotically responsive, non-seed-specific dehydrins accumulated to high levels in the recalcitrant cotyledons compared with orthodox seeds. Next, M. truncatula mutants of the ABSCISIC ACID INSENSITIVE3 (ABI3) gene were characterized. Mature Mtabi3 seeds were found to be desiccation sensitive when dried below a critical water content of 0.4g H2O g DW–1. Characterization of the LEA proteome of the Mtabi3 seeds revealed a subset of LEA proteins with severely reduced abundance that were also found to be reduced or absent in C. australe cotyledons. Transcripts of these genes were indeed shown to be ABI3 responsive. The results highlight those LEA proteins that are critical to desiccation tolerance and suggest that comparable regulatory pathways responsible for their accumulation are missing in both desiccation-sensitive genotypes, revealing new insights into the mechanistic basis of the recalcitrant trait in seeds.

Inference of Longevity-Related Genes from a Robust Coexpression Network of Seed Maturation Identifies Regulators Linking Seed Storability to Biotic Defense-Related Pathways

“…This uncoupling suggests that the acquisition of these traits is controlled in part by independent regulatory pathways. To test this hypothesis and further elucidate the extent to which genes in the DT and longevity modules are under regulation of ABI3, we analyzed the transcriptomes of the desiccation-sensitive seeds of M. truncatula abi3 mutants at 32 and 40 DAP (Delahaie et al, 2013;Verdier et al, 2013) (Supplemental Data Set 5). These time points coincide with an increase in the transcript levels of the longevity-correlated genes in wild-type seeds.…”

“…Longevity was determined for each of the 49 developmental stages of each environmental growth condition as the storage time that was needed to decrease the germination of the seed population to 50% (P50), derived from survival curves of percentage of final germination over storage time (75% RH, 35°C). The M. truncatula abi3 mutant (NF6003) was isolated and backcrossed twice with wild-type plants as described by Delahaie et al (2013). Seeds of abi3 mutants and the wild type (R108) were collected at 40 DAP and frozen for transcriptome analysis.…”

Regulatory network analysis reveals novel regulators of seed desiccation tolerance in Arabidopsis thaliana

“…In angiosperms, DT is acquired at the seed maturation stage, which involves a complex regulatory network (3,4) that activates a large subset of genes involved in a number of mechanisms that influence seed survival in the dry state. The set of genes required for seed DT includes genes encoding protective proteins such as late embryogenesis abundant (LEA) (5,6) and heat shock proteins (HSPs) (7), enzymes involved in scavenging reactive oxygen species (8) and the biosynthesis of protective compounds such as oligosaccharides (3,9), and antioxidants such as tocopherols and flavonoids (10,11).…”

Orthodox Seeds and Resurrection Plants: Two of a Kind?

“…ABI3 was originally discovered as a seed-specific transcription factor but has since been shown to function in abiotic stress responses in the vegetative tissues of desiccation-tolerant and -sensitive angiosperm plants (Khandelwal et al, 2010;Mönke et al, 2012;Delahaie et al, 2013;Bedi et al, 2016). In Arabidopsis, ABI3 controls the middle to late stages of embryo maturation, the acquisition of seed DT, and the expression of several genes, including LEA genes, especially during stress recovery (Delmas et al, 2013;Bedi et al, 2016).…”

“…In Arabidopsis, ABI3 controls the middle to late stages of embryo maturation, the acquisition of seed DT, and the expression of several genes, including LEA genes, especially during stress recovery (Delmas et al, 2013;Bedi et al, 2016). Mature seeds of M. truncatula abi3 mutants are desiccation sensitive (Delahaie et al, 2013). Structural homologs of ABI3 have been identified in angiosperm resurrection species (Bartels and Salamini, 2001;Costa et al, 2017).…”