Ethylene Biosynthesis - Fruit Ripening: Physiology, Signalling and Genomics - page 193

Ailsa Craig rin

Days M B 3 7 36 42 48 54 60

LeACS1A

LeACS2

LeACS4

LeACS6

rRNA

Fig. 10.6. Expression of different ACS genes during ripening of tomato. Note that LeACS6 is expressed
before ripening and then rapidly decreases in amount. LeACS1A , on the other hand, is expressed early in
ripening, together with LeACS2 and LeACS4 , but the latter two mRNAs persist for longer. In fruit of the
ripening inhibitor ( rin ) mutant, which fails to ripen even over a period of several weeks, LeACS2 and
LeACS4 are not upregulated and LeACS6 is not repressed, because there is no normal ethylene response in
the mutant. M, mature green fruit, prior to ripening onset; B, breaker fruit (fi rst sign of colour change). Days
indicate days after breaking. Hybridization signals to fruit RNA samples were detected by X-ray fi lm.
LeACS1A and LeACS6 expression was much lower than that of the other ACS genes detected. Exposure
times to the fi lm (a measure of signal strength) were as follows: LeACS1A , 7 days; LeACS2 , 20 h; LeACS4 ,
20 h; LeACS6 , 16 days. From Barry et al. (2000).

et al ., 2000). A modifi ed version of this
scheme, proposed by Yokotani et al .
(2009), is shown in Fig. 10.7.
Auxins, gibberellins and cytokinins all
affect ethylene production in particular
tissues and only a few examples will be
discussed here. ACO1 expression increased
when beech ( Fagus sylvatica L.) seeds were
treated with gibberellic acid 3 (GA 3 ) or
ethephon (which generates ethylene in
plants) (Calvo et al. , 2004). The stimulation
by ethephon was reversed by the GA
biosynthesis inhibitor paclobutrazol, sug-
gesting that ethephon affects GA pro-
duction. Auxin increases the rate of
ethylene production and RNA synthesis in
seedlings (Grierson et al. , 1982) and
induces a subset of ACS genes (Tsuchisaka
and Theologis, 2004; Salman-Minkov et al. ,
2008). The expression of auxin-induced

OsACO2 in rice ( Oriza sativa ) seedlings is
partially inhibited by ethylene, while
ethylene induction of OsACO3 tran-
scription is completely blocked by auxin
(Chae et al. , 2000).

10.4 Transcriptional Regulation of ACO
and ACS Genes

Given the existence of many ACO and ACS
gene family members, and considering the
range of developmental, environmental and
hormonal factors that infl uence their
expression, it is important to identify the
TFs that regulate the transcription of
individual genes in order to understand the
complexities of controlling ethylene bio-
synthesis. Progress has been slow in this
area, but four TFs have now been identifi ed