Napins
2DE of the napin-enriched fraction resulted in 18 protein spots in the pH range of 9-12 (Figures 4C, D), similar the pI of ~11 reported for B. napus napin (Crouch et al., 1983). Eight genes encoding napin have been identified in camelina (Supplementary Table S1; Nguyen et al., 2013), of which four (CsNap-1-G1, CsNap-1-G3, CsNap-3-G3 and CsNap-4-G1) contributed between 12.1% and 100% of the combined total napin per spot (Table 3, Supplementary Table S3). CsNap-3-G3 and CsNap-4-G1 were present in all 18 2DE spots, whereas CsNap-1-G1 and CsNap-1-G3 were present in 17 and 12 spots, respectively. The number of amino acid residues in these eight napin isoforms ranged from 161 (CsNap-3-G1) to 166 (CsNAP-3-G3; Supplementary Figure S3). Late embryogenesis abundant (LEA) proteins also were present in the napin-enriched fraction (Table 3). Brassica seed LEA proteins are basic with a pI > 7 and have disordered secondary structures (Amara et al., 2014). They are small proteins of ~10 kDa to 30 kDa and accumulate in the embryo during the late stages of seed development (Hong-Bo, et al., 2005). The non-napin polypeptide bands observed at ~15 kDa in the 1DE separation of the napin-enriched fraction (Figure 3C) may be LEA proteins. The LEA proteins contribute to seed longevity and germination by associating with other proteins (e.g., enzymes) and stabilizing their structure during episodes of environmental stress, such as dehydration during seed maturation (Hand et al., 2011). The considerable amount of LEA proteins in camelina seed may be related to its strong drought tolerance making it a suitable crop in arid, low soil moisture areas (Eynck and Falk, 2013).