Identification and expression of new Fragaria x ananassa aquaporins in different tissues and during strawberry development.

Aquaporins are water channels that facilitate passive water transport across inter- and intracellular membranes. They regulate water transport at cellular level. As they are responsible for intra- and intercellular water transport, they have the potential to profoundly impact on a wide variety of physiological processes. There are several types of aquaporins. Yet, the plasma membrane intrinsic proteins (PIPs) and tonoplast intrinsic proteins (TIPs) are thought to affect plant water relations the most due to their abundance and subcellular location. Only a few aquaporins have been identified in Fragaria up to now, hampering further research in many physiological processes involving aquaporins, such as fruit ripening and adaptation to drought stress. In order to pave the way for future research, we identified several Fragaria x ananassa PIPs and TIPs.
In order to determine their expression profile across vegetative tissues and during fruit development, we grouped them into three PIP subtype 1 groups (group FaPIP1;1, group FaPIP1;2 and group FaPIP1;3), three PIP subtype 2 groups (FaPIP2;1,(a), FaPIP2;1(b) and FaPIP2;2) and two TIP groups (TIP(a) and TIP(b)), based on sequence similarities. RT-qPCR analysis on each of these eight groups revealed that group FaPIP1;2 is ubiquitously expressed, suggesting a constitutive role in cell-to-cell water transport. Group FaPIP1;3 is almost leaf-specific. Group FaPIP2;1 is upregulated during fruit ripening, while genes belonging to groups FaPIP1;1 and FaPIP2;2 are downregulated during fruit ripening. The TIPs analysed here are hardly expressed in leaves. Group TIP(a) is downregulated during fruit ripening. These findings suggest functional specialization among aquaporins, even within the same (sub)class.
Now these sequences are available and it is known in which tissues they are mainly expressed, further research can investigate their function in regulating plant water relations. Of particular interest are their response to drought stress and their contribution to drought tolerance.