Vacuolar Phosphate Transporter1 (VvVPT1) positively regulates grape
berry soluble sugar accumulation and ripening
Abstract
Vacuolar Phosphate Transporter1 (VPT1)-mediated phosphate uptake in the
vacuoles is essential to plant development and fruit ripening.
Interestingly, in this study, we find that the VvVPT1 protein positively
regulates grape berry soluble sugar accumulation, potentially associated
to its sugar transport activity. The VvVPT1 is isolated from
grape ( Vitis vinifera) berries, which mainly accumulated glucose
and fructose. This tonoplast-localized VvVPT1 contains SPX
(Syg1/Pho81/XPR1) and MFS (major facilitator superfamily) domains and
its mRNA expression could be induced by sucrose. Using transient
transgenic systems in grape berry, we found that the downregulation and
upregulation of VvVPT1 expression inhibited and promoted ripening
and affected hexose contents, fruit firmness, and ripening-related gene
expression. The VvVPT1 protein has low affinity for Pi, while possesses
high affinity for hexose absorption in yeast system, dependent on its
SPX domain. In conparision to the VPT1 available (only strawberry FaVPT1
and Arabidopsis AtVPT1), as expected, the three proteins all have
low-affinity Pi transport activity, strickingly, they appear different
sugar transport capacity, in consistent with their soluble sugar status.
Together, these data first demonstrate that VvVPT1 can promote grape
berry hexose accumulation and ripening, associated to its SPX and MFS
domains in direct transport of hexose into the vacuole. Finally,
vacuolar phosphate transporter1 (VPT1)-mediated alternative accumulation
of soluble sugar varies with fruit types is discussed.