A computational study on the structure-function relationships of plant caleosins

Abstract

Plant cells store energy in oil bodies constructed by structural proteins such as oleosins and caleosins. Although oil bodies usually accumulate in the seed and pollen of plants, caleosins are present in various organs and organelles. This issue, coupled with the diverse activities of caleosins, complicates the description of these oleo-proteins. Therefore, the current article proposes a new classification based on the bioinformatics analysis of the transmembrane topology of caleosins. Accordingly, the non-membrane class are the most abundant and diverse caleosins, especially in lower plants. Comparing the results with other reports suggests a stress response capacity for these caleosins. However, other classes play a more specific role in germination and pollination. A phylogenetic study also revealed two main clades that were significantly different in terms of caleosin type, expression profile, molecular weight, and isoelectric point (P < 0.01). In addition to the biochemical significance of the findings, predicting the structure of caleosins is necessary for constructing oil bodies used in the food and pharmaceutical industries.

Figure 1

Caleosin classification according to the transmembrane topology by Phobius. The signal peptide, cytoplasmic and non-cytoplasmic regions are indicated with red, green and blue lines, respectively. The purple line shows the hydrophobic analysis by ProtScale. The zero score is drawn with a black dashed line.

Figure 2

(a) The frequency of subcellular locations for each caleosin class. (b) The percentage of each caleosin class in the major clades of plants. The caleosin classes have been named based on the order of non-cytoplasmic (N) and cytoplasmic (C) domains.

Figure 3

The average expression of the caleosin classes in each tissue. The caleosin classes have been named based on the order of non-cytoplasmic (N) and cytoplasmic (C) domains.

Figure 4

Expression profile of wheat caleosins through different developmental stages. The caleosin classes have been named based on the order of non-cytoplasmic (N) and cytoplasmic (C) domains. Moreover, the phylogenetic clade (I or II) is mentioned next to the name of each caleosin class. DPA: days post-anthesis; DAP: days after pollination.

Figure 5

The differential expression of caleosins in response to 20 Mm abscisic acid. The data was extracted from the Expression Atlas database. The caleosin classes have been named based on the order of non-cytoplasmic (N) and cytoplasmic (C) domains. Moreover, the phylogenetic clade (I or II) is mentioned next to the name of each caleosin class.

Figure 6

(a) Transmembrane topology of caleosins detected by Philius, Phobius, PolyPhobius, OCTOPUS, SCAMPI, SPOCTOPUS, and TOPCONS. (b) The frequency of the same results between Phobius and other algorithms and the diversities resulting from the number of TM, domain order or both.