The Molecular Basis of ABA-Mediated Plant Response to Drought - Abiotic Stress: Plant Responses and Applications in Agriculture - page 112

In many cases, not only structural proteins, such as ion channels are conserved between
Arabidopsis and other plant species, but also regulatory proteins, such as transcription
factors. In addition, it is worth adding that entire transcriptional regulons can also be
conserved, as in case of the ABA signalosome PYR/PYL/RCAR-PP2Cs-SNRKs. 'Only after
we understand how plants respond to stress — in many cases first in Arabidopsis and
then applying the Arabidopsis model to crop plants — will we be able to begin engi‐
neering stress tolerance' [100].
During the last decade, microarrays have become a routine tool for the analysis of tran‐
scripts, not only in model Arabidopsis but also in crops, such as barley and rice. Interesting‐
ly, interspecies comparisons between distantly related species, Arabidopsis and rice or
barley revealed conserved patterns of expression in the case of many orthologs genes
[101-103]. Comparative analyses showed that orthologous of specific genes in rice or barley
are also responsive to stress similar to Arabidoposis [103; 102]. Mochida et al. [104] used
publicly available transcriptome data to investigate regulatory networks of the genes in‐
volved in various developmental aspects including drought in barley. On the basis of a com‐
parative analysis between barley and model species, such as Arabidopsis or Brachypodium,
modules of genes putatively involved in drought response have been identified. In addition
to these computational approaches, Moumeni et al. [105] have undertaken a comparative
analysis of the rice root transcriptome under drought stress. They used two pairs each of
drought-tolerant and susceptible rice NILs (Near Isogenic Lines). Global gene expression
analysis revealed that about 55% of the genes differentially expressed were in rice roots un‐
der drought stress. The drought-tolerant lines showed an up-regulation of the genes in‐
volved in secondary metabolism, amino acid metabolism, response to stimulus, defense
response, transcription and signal transduction. Proteomic analysis of drought-sensitive and
drought-tolerant barley lines performed by Kausar et al. [106] revealed an increased level of
metabolism, photosynthesis and amino acid synthesis-related proteins in tolerant geno‐
types, whereas a decreased level was observed in sensitive forms. The data confirmed the
results described previously in other species and should that similar processes play a signifi‐
cant role in barley's adaptation to stress conditions.
5. The huge role of tiny molecules (microRNA) in drought response
Small non-coding RNAs - miRNAs, which were first reported in the nematode Ceanorhabdi‐
tis elegans in 1993 [107] and which are responsible for the phenomenon of RNA interference,
have become recognized as very important regulatory components of the cell signaling.
miRNAs have been shown to be highly conserved gene expression regulators across species
[108-109]. The first plant miRNA was isolated from Arabidopsis [110]. To date, approximate‐
ly 5000 plant miRNAs have been identified and deposited in miRbase (19.0 release) includ‐
ing 299 miRNA from Arabidopsis, 135 from Brachypodium, 206 from sorghum, 42 from
wheat, 591 from rice, 172 from maize and 67 from barley [111]. miRNAs are small regulatory
RNAs of a 20-22 nucleotide length that are encoded by endogenous MIR genes. Their pri‐
mary transcripts are partially double-stranded stem-loop structures. Pri-miRNAs in plants