Phylogenetic and Expression Analysis of Pear Yellow Stripe-Like Transporters and Functional Verification of PbrYSL4 in Pear Pollen

Yellow stripe-like (YSL) family transporters, belonging to the oligopeptide transporter family, are significant iron transport proteins. In this study, we provided a genome-wide identification and analysis of the YSL gene family in Pyrus bretschneideri. We found eight YSL gene members in pear, clustered into four main groups in the phylogenetic tree. Segmental duplication has played a key role in the expansion of the pear YSL family. The pollen activity analysis indicated that the low concentration of iron ion was beneficial to both pear pollen germination and pollen tube growth. Among the eight YSL genes, PbrYSL4 had particularly high expression in all pear tissues; it was significantly responsive to change in the external iron ion supply in the pollen cultivation in vitro. Moreover, expression of PbrYSL4 in yeast mutant Delta ccc1 (Ca2+-sensitive cross-complementer 1 mutant) made Delta ccc1 restore growth in high iron medium. These data together suggest that PbrYSL4 was involved in the movement of iron in the pear pollen tube growth.