Coconut - Genomics of Cultivated Palms - page 19

and analyzed by X-ray diffraction. Crystals of cocosin are rhombohedral with space
group R3 with 92.829, 92.829, and 215.290Å dimension [45] . The composition of a
high proportion of medium-chain fatty acids is an important feature of coconut oil.
LPAAT (1-acyl-Sn-glycerol-31 acyl transferase) lysophosphatidyl acyl transferase
is an important enzyme that catalyzes conversion of lysophosphatidic acid (LPA)
to phosphatidic acid (PA). Activity of the LPAAT enzyme shows a preference for
medium-chain length fatty acyl-coenzyme A substrates. The gene controlling the
LPAAT enzyme is cloned [7] and sequenced, and is 1.325 kb in size (U29657) with
an anticipated protein of 308 amino acids ( Table 2.3 ). Promoter of the LPAAT gene
of 1.2 kb size has recently been sequenced, and contains TATA box, CAAT box,
Skn-1 motif, W box, AGGAA, and TCCC motifs [46] .
MicroRNAs are small regulatory RNA molecules 20-22 nucleotides long. They
negatively regulate the expression of target by post-transcriptional gene silencing.
About 179 microRNAs (miR) were investigated at China by authors of [47] using
microRNA chip, of which 95 are expressed in the immature and 176 are expressed
in the mature stage of endosperm. Twenty-three miRs were upregulated and 9 were
down-regulated in mature endosperm. Computational analysis identified the 32 target
genes for these coconut miRs. Three miRs (Ath-miR398a, b, and bna-miR397a miRs)
displayed unique expression only in immature endosperm. Laccase was identified as a
target gene for the unique miR [47] . Free nucleotides present in the coconut endosperm
were analyzed and were found to be natural miRNA:mRNA hybrid molecules [48] .
Makapuno, also spelled as macapnuo and called variously in different loca-
tions ghee coconut, sap, Coco Gra, kopyor, and Dikripol (review: 4), is a delicacy
in coconut. It is due to a mutation [49] at a single mendelian gene (mm), where the
endosperm becomes buttery and jelly-like rather than like a common solid endosperm
(MM). Makapuno embryos cannot germinate in nature due to this deleterious allele
causing the endosperm-hindering embryo germination. But the plants having het-
erozygous locus for the makapuno mutation (Mm) produce normal (MM/Mm) and
makapuno (mm) fruits based on the gamete received from normal (M) and Makapuno
(m) pollen cells, respectively. Biochemical analysis revealed the macapuno fruits to
have 8300-fold-reduced activity of the enzyme alpha galactosidase compared to nor-
mal fruits [50] . Free nuclei of the coconut endosperm have the potential to be a biore-
actor for expressing recombinant proteins [51] .
2.5 Coconut Tissue Culture-Related Genes
Tissue culture of oil and date palms is successful and commercially practiced. But
the technique is still being standardized in coconut, with nonrepeatable results.
A review of coconut biotechnologies, especially in in vitro propagation [52] , gives
some background of the past work. Sequencing of a few genes controlling the
somatic embryogenesis, such as cyclic dependant kinase (CDKA-) [53] , knotted-like
homeobox (KNOX-) [54] , and somatic embryogenesis receptor kinase (SERK-) [55] ,
has resulted in important information ( Table 2.3 ). The details of the genes, their role,