Pollen aquaporins NIP4;1 and NIP4;2 are required in Arabidopsis reproduction

PEREZ, J; SOTO, G; AMODEO, G; MUSCHIETTI, JP

Portland, Oregon

Congreso; Annual meeting of the American Society of Plant Biologists; 2014

American Society of Plant Biologists

In Angiosperms, reproduction involves processes where water and solutes transport is finely regulated temporally and spatially. In plants with dry stigmas, regulated pollen hydration provides an effective early barrier to incompatible pollinations. Water, nutrients, and other small molecules are transported rapidly into the grain from the stigma papillae to promote pollen germination. Then, additional entry of water and solutes into the pollen tubes allows cytosolic adjustment of ions and turgor pressure necessary for tip growth. Aquaporins may mediate water and solute transport during pollen germination and/or pollen tube growth. In Arabidopsis thaliana only 4 aquaporin genes (out of 35 loci) are specifically expressed in mature pollen: AtTIP5;1, AtTIP1;3, AtNIP4;1 and AtNIP4;2. Interestingly, AtNIP4;1 and AtNIP4;2 are genes with high nucleotide sequence identity, similar gene structure and disposed in tandem. At protein level, they have 85% amino acidic identity, and share the same two NPA motifs and the ar/R selectivity filter residues (W, V, A and R) involved in transport selectivity. However, based on quantitative PCR and promoter::GUS experiments, they displayed different expression patterns. While AtNIP4;1 is lowly expressed in mature pollen and pollen tubes, AtNIP4;2 increased their levels 30-fold upon pollen germination. Single and double mutant plants showed affected fertility parameters such as reduced number of seeds per silique and distorted segregation ratios. Furthermore, double mutant plants displayed reduced mature pollen grain diameter, increased number of pollen grains arrested at uni- and bi-cellular stages, reduced germination rate and pollen tube length, and increased percentage of non-pollinated flowers. We generated complementation lines expressing eGFP-tagged AtNIP4;1 and AtNIP4;2 to study their subcellular localization. Our results suggest that AtNIP4;1 and AtNIP4;2 could have a functional redundancy during reproduction, even though they may play different roles in pollen development, pollination and/or fertilization.