Biology Reference
In-Depth Information
GA Suppresses DELLA to Upregulate the JA-Biosynthesis
Gene LOX1 and DAD1
Considering the fact that JA application was able to induce the expression of
MYBs in the ga1-3 gai-t6 rga-t2 rgl1-1 mutant it is reasonable to argue that JA
biosynthesis, instead of JA signaling pathway, is likely affected in the ga1-3 gai-
t6 rga-t2 rgl1-1 mutant. To test this hypothesis, we examined the expression of
known or putative JA biosynthesis genes including DAD1 (Defective in anther
dehiscence 1), LOX1 (Lipoxygenase 1), LOX2 (Lipoxygenase 2), AOS (Allene ox-
ide synthase), AOC1 (Allene oxide cyclase 1, At3g25760), AOC 2 (At3g25770),
AOC 3 (At3g25780), AOC 4 (At1g13280) and OPR3 (OPDA reductase 3) in
La-er WT, Ws WT, ga1-3 single, ga1-3 gai-t6 rga-t2 rgl1-1 quadruple, ga1-3 gai-
t6 rga-t2 rgl1-1 rgl2-1 penta, and opr3 mutants. We found that only MYB21,
LOX2 and AOC1 showed reduced expression in the opr3 mutant whereas all the
other genes, including GA-biosynthesis genes, expressed similarly in the opr3 mu-
tant and Ws WT control (Figure 6A and 6B), suggesting that JA-deficiency does
not affect GA biosynthesis. Expression of these genes in GA-related mutants was
more complicated. We found that the expression levels of AOS, AOC1, AOC3,
AOC4, LOX2 and OPR3 did not show significant differences in all GA-related
mutants when compared to the La-er WT control (Figure 6A and 6B), suggesting
these genes are probably regulated in a GA-independent fashion. The expression
of AOC2 was obviously induced in ga1-3 and then reduced to the WT level in
the quadruple and penta mutants (Figure 6A), suggesting AOC2 is a GA-down
gene. In contrast, the expression of LOX1 was significantly reduced in ga1-3 but
was restored both in the ga1-3 gai-t6 rga-t2 rgl1-1 quadruple and penta mutants
(Figure 6B), suggesting that although LOX1 is a GA-up gene and its expression is
not repressed by RGL2. Interestingly, DAD1 expression was found to be down-
regulated to approximately 20% of the WT level in both ga1-3 and the ga1-3 gai-
t6 rga-t2 rgl1-1 quadruple mutant whereas was restored to approximately 60%
of the WT level in the penta mutant (approximately three folds increase in penta
versus Q3) (Figure 6A and 6C), indicating that GA may regulate DAD1 expres-
sion via suppression of RGL2.
JA Levels Are Greatly Reduced in the Young Flower Buds of
the ga1-3 gai-t6 rga-t2 rgl1-1 Quadruple Mutant
One expected consequence of downregulation of DAD1 expression by RGL2
is the reduction of JA levels in the ga1-3 gai-t6 rga-t2 rgl1-1 quadruple mu-
tant (Q3). To text this hypothesis, we measured the JA contents in the young
flower buds in WT, opr3, the Q3 quadruple mutant and the ga1-3 gai-t6 rga-t2
rgl1-1 rgl2-1 penta mutant (penta). The data obtained clearly showed that the JA
