2. Materials and methods
2.1. Plant materials
Plants were grown from seed in Metro-Mix
360®, watered daily and fertilized with a controlled
release fertilizer, Osmocote® (14-14-14). The plants
were maintained in a greenhouse on the NMSU
main campus. The RNA for the cDNA library
construction was isolated from placental fruit tissue
of plants grown in the field at the Fabian
Garcia Research Center, NMSU, Las Cruces.
Typical capsaicinoid content of the chile
germplasm used in this report is listed in Table 1.
Capsaicinoid content of chile fruit was determined
using an HPLC method [25]. Essentially
fruit is dried, ground to a powder and extracted
with acetonitrile. An aliquot is then injected into a
Waters HPLC equipped with a fluorescence detector
and the samples are resolved on C-18 reverse
phase columns.
2.2. Nucleic acid isolation and blot analyses
Total RNA and genomic DNA were prepared
as described earlier [26]. Plant tissues to be extracted
for RNA were collected directly into liquid
N2. RNA blots were prepared after electrophoresis
of ethidium bromide stained RNA samples [27].
Genomic DNA was digested with restriction endonucleases
following the supplier’s buffer recommendations,
for at least 4 h at 37°C.
Pre-hybridization, hybridization and washing conditions
were as described earlier [26]. In one experiment,
transcript levels were quantified using a
Molecular Dynamics Storm 860 phosphorimager.
In this case, the blots were re-probed with a
fragment of the chile gene for 25S ribosomal RNA
to normalize transcript abundance. All northern
displays were replicated at least once with independently
isolated RNA preparations.
2.3. cDNA library construction
Fruit were collected from C. chinense c.v. haban
˜ero grown at the Fabian Garcia Research Center,
Las Cruces, NM. The fruit were sorted into
three different developmental stages based on size
and color development: (1) green fruit; (2) fruit
with developing orange color, and (3) fully orange
fruit. The placental tissue was dissected from the
fruit and RNA isolated from each of the three
stages. PolyA RNA was prepared from the placental
tissue of stage 1 using a batch oligo-dT
process and a cDNA library of these transcripts
was generated in Lambda ZapII (Stratagene). The
primary library was titered at 2.5105 recombinant
pfu:ml, and then amplified to a titer of
11010 recombinant pfu:ml. This library was differentially
screened using radiolabeled first strand
cDNA from placental transcripts from either immature
haban˜ero fruit or from immature non-pungent
C. chinense (PI 1721) fruit. Plaques which
hybridized strongly to the haban˜ero probe and not
to the non-pungent C. chinense were purified and
characterized.
2.4. DNA sequencing and alignments
DNA sequences were determined on recombinant
plasmids using dideoxy termination methods,
SequiTherm EXCEL kit (Epicentre Technol) and
a LI-COR automated DNA sequencer. DNASTAR
software was used to assemble and analyze
DNA sequences; DNA and predicted amino acid
sequences were searched against DNA and protein
databases using BLAST 2.0 [28] at the NCBI web
site (www.ncbi.nlm.nih.gov:BLAST:); in some
cases against the BLOCKS database ([29];
www.blocks.fhcrc.org:) or analyzed by PSORT to
predict sub-cellular sites of accumulation ([30];
psort.nibb.ac.jp:8800:). The nucleotide sequence
data are in the GenBank Nucleotide Sequence
Database under accession numbers: Pal AF081215
(phenylalanine ammonia lyase); Ca4h AF088847
(cinnamate 4-hydroxylase); Comt AF081214 (caffeic
acid 3-O-methyl transferase); Kas AF085148
(3-keto-acyl acyl carrier protein (ACP) synthase);
pAmt AF085149 (putative amino transferase);
rrn25 AF088849 (25S ribosomal RNA).