Cell wall O-acetylation is modified by drought
In this study, we found statistically significant enrichments inO -acetyl ester content of bulk leaf cell walls (AIR) in response
to drought stress (Fig. 10b ). In contrast, cell wall monomer
composition, which was dominated by galacturonic acid from pectin,
changed little over seven days following the cessation of watering
(Fig. 10a ). That leaf AIR monosaccharide content was largely
insensitive to drought suggests a slower turnover in monosaccharide cell
wall polysaccharides than the fast time scales of days observed for
changes in volatile emission signatures and cell wall O -acetyl
ester content changes (1-7 days). O -acetyl-substituents are
present on nearly all cell wall polymers with the exception of
cellulose, whereas methyl esters are thought to be primarily associated
with pectin
(Derbyshireet al., 2007). O -acetyl esterification of plant cell
walls is known to play important physicochemical, mechanical, and
structural roles that serve to minimize degradation while enhancing
intermolecular interactions with other wall polymers
(Biely,
2012). Studies have shown that cell wall O -acetylation of
hemicellulose and pectin is critical for proper plant growth and
functioning. For example, simultaneous mutations of the acetyl
transferase genes TBL32 , TBL33 andTBL29 /ESK1 in Arabidopsis resulted in a severe
reduction in xylan O -acetyl level down to 15% that of the wild
type, and concomitantly, severely collapsed vessels and stunted plant
growth
(Yuanet al., 2016). Additional studies demonstrated thatArabidopsis plants with defective ESK1 enzymes have a
constitutive drought syndrome and collapsed xylem vessels, low hydraulic
conductivity along with low O -acetylation levels in xylan and
mannan, low transpiration rates, high water use efficiency, and
dwarfism
(Lefebvreet al., 2011; Ramírez et al., 2018). Together with these
studies, the observation of enhanced leaf cell wall O -acetylation
during drought (Figure 10b ) suggests that polysaccharideO -acetylation is important for the proper functioning of vascular
tissues under hydraulic stress.