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).