New Insights into Desiccation-Associated Gene Regulation by Lilium longiflorum ASR during Pollen Maturation and in Transgenic Arabidopsis - International Review of Cell and Molecular Biology - page 73

4.4.1. Gene Identification and Cross Talk among LLA23-, Glucose-, and
Drought-Inducible Responses
The Venn diagram in Fig. 2.5 shows that 101, 293, and 166 genes were
identified as LLA23-, glucose-, and drought-inducible genes with at least
two and halffold induction of expression in LLA23-overexpressing plants
or at least sixfold induction of expression in the glucose and the drought
treatment. Although drought is considered to be the most severe stress that
affects plant growth, the number of glucose-inducible genes is more pro-
nounced than that of drought-inducible genes, which suggests that aside
from osmotic stress, glucose acts as a metabolic signal that regulates the
expression of many genes via diverse mechanisms in the cell. Of the three
treatments, the least effective one is the group of genes induced by LLA23,
which indicates that genes affected by ASR represent only a small fraction
of the stress-inducible genes. These genes include substantial amounts of
reported drought and osmotic stress-inducible genes, which indicates that
the microarray system for finding these genes is functioning properly.
The Venn diagram analysis reveals difference and cross talk in gene
expression among the drought-, glucose-, and ASR-induced responses
( Fig. 2.5 ). Up to 82 genes were identified as glucose- and LLA23-inducible
genes, whereas only 30 genes were induced by both drought and LLA23-
overexpressing treatments, and 72 genes were induced by both glucose
and drought. Li et al. (2006) have reported that genes induced by both
glucose and ABA are involved in stress responses, indicating overlapping
regulation by glucose and ABA. Moreover, 25 genes were induced under all
three stresses, as indicated by the cross in Table 2.2 . These genes encoding
functional proteins such as detoxification, LEA, transporter, cell wall- and
defense-related proteins that probably function in stress tolerance and others
are involved in carbohydrate metabolism, secondary metabolism, amino acid
and protein metabolism, transcript regulation, and signal transduction. These
results indicate a strong association in the expression of stress-responsive
genes among the three signaling transduction pathways. Despite the dense
overlaps among glucose-, drought-, and LLA23-inducible genes, we found
a substantial amount of stress-inducible genes that were highly induced by
each treatment. These highly inducible genes are discussed in the following
section.
4.4.2. Highly Stress-Inducible Genes
Among the stress-inducible genes identified, substantial amounts of genes
are highly induced by each stress. In this study, genes with expression ratios