Comparative Proteomics of Recalcitrant Seed Death in Spartina alterniflora.

Spartina alterniflora is a dominant salt marsh species along the U.S. Atlantic and Gulf Coasts, and its establishment is important in reducing coastal erosion in Louisiana. However, long-term preservation of S. alterniflora is challenging because the seeds are recalcitrant, losing viability when dried below 45% water content.

Comparative proteomics between S. alterniflora and orthodox, desiccation tolerant S. pectinata seeds was performed to identify heat-stable (soluble after 40 min at 95⁰C) proteins that may be associated with desiccation tolerance. The heat-stable proteomes of S. alterniflora and S. pectinata contain 174 and 312 spots, respectively, as resolved by two dimensional gel electrophoresis and detected by in silico software analysis (Nonlinear Progenesis). Eighty-five unique spots were present in orthodox S. pectinata but were missing in recalcitrant S. alterniflora. Some have been sequenced so far, and several proteins share homologies to known sequences for group-3 late embryogenesis abundant proteins (LEAs), dehydrin (group-2 LEA), cystatin (cysteine protease inhibitor), superoxide dismutase, peroxiredoxin, stress-responsive protein, nascent peptide associated complex (NAC), abscisic stress ripening protein, glyceraldehyde-3-phosphate dehydrogenase and ubiquitin; these proteins are associated with the desiccation-tolerant state in other organisms.

Gels stained with PRO-Q Diamond revealed phosphorylated cystatins (ca. 27 kDa) that were highly expressed in S. pectinata but not in S. alterniflora. Differentially expressed glycosylated proteins (ca. 20 kDa and 60 kDa, detected with PRO-Q Emerald 300 stain) were uniquely expressed in S. pectinata. These data suggest that a modestly-sized suite of proteins and post-translational modifications confer desiccation tolerance to S. pectinata seeds, and demonstrate the utility of the comparing related species to understand physiological processes.