3.7 Effect of drought on phytohormones metabolism and signaling
The expression profiles of IAA, ABA and JA metabolic and signaling genes
based on RNA-Seq data and their corresponding endogenous contents were
analyzed. A total of 38 DEGs encoding enzymes involved in auxin
metabolism (17) and signaling (21) were at least regulated at one stage
(Table S10). The IAA biosynthesis gene, SlTAR2, was significantly
down-regulated at PMC-MEI stage, whereas SlTAR1-like ,SlTAR 2, ToFZY1 and ToFZY2 were significantly
up-regulated at TED-VUM stage (Figure 7C). Consistently, the content of
endogenous IAA was significantly reduced at PMC-MEI stage whereas it was
moderately increased at TED-VUM under DS condition (Figure 7B).
A total of 19 DEGs associated with ABA metabolism and signaling were
identified (Table S10). At PMC-MEI stage, two dehydrogenase/reductase
genes, 3-oxoacyl-CoA reductase 1 and SlSDR12-like involved
in ABA biosynthesis were significantly up-regulated, whileSlcyp707a1, encoding ABA 8สน-hydroxylase involved in ABA
catabolism, was markedly induced. Correspondingly, the core components
of ABA signaling genes including one ABA receptor, SlPYL9 , twoprotein phosphatase 2C (PP2C ) genes (SlPP2C37 andSlDIG3), and two SNF1-RELATED PROTEIN KINASE2 (SnRK2 )
genes (SlSRK2C and AY222455 ) were significantly
up-regulated (Figure 7). Additionally, two known direct downstream
transcription factor targets of SnRK2, SlAREB , homologue ofAtAREB2 and SlABF , homologue of AtABF3 (Figure S2B)
which are regulators of ABA-responsive genes, were exclusively
significantly up-regulated at PMC-MEI stage, suggesting that ABA
signaling is induced early in anther development under drought stress.
At TED-VUM stage, only SlSDR12-like and SlDIG3 were
significantly up-regulated and only a few genes were moderately induced
at BIN-MP stage such as Slcyp707a1 , SlPP2C37 andSlSRK2C (Figure 7), suggesting that ABA signaling is impaired
under drought condition at TED-VUM and BIN-MP stages. Consistently,
endogenous ABA content was significantly increased at PMC-MEI and
TED-VUM stages with an increase of 205% and 395%, respectively (Figure
7B). Together, these results suggest that ABA, in conjunction with its
catabolic gene might play a significant role in drought tolerance
mechanism in the early stages of anther development.
A total of 21 DEGs associated with JA metabolism and signaling were
recognized in at least one stage (Table S10). RNA-Seq analysis of four
genes involved in JA biosynthesis revealed that at PMC-MEI stage,SlLOX5 exhibited significant increase. At TED-VUM and BIN-MP
stages, all four genes: SlLOX5 , SlOPR3 ,Phospholipase A2 and SlAOC were down-regulated under
drought stress although none was significant at BIN-MP stage (Figure
7C). Invariably, under DS, endogenous JA contents were significantly
decreased at TED-VUM and BIN-MP stages (Figure 7B).