Unraveling the complex roles of genes in the PIRL family on Arabidopsis pollen development

The PIRL family is a group of nine recently identified Arabidopsis genes encoding a novel class of plant leucine-rich repeat (LRR) proteins. Two of these genes, PIRL1 and PIRL9, have redundant roles critical in pollen development. PIRL2 and PIRL3 are the closest relatives of PIRL1 and PIRL9, comprising the PIRL Subfamily I. Because PIRL2 and PIRL3 are closely related to PIRL1 and PIRL9, it was hypothesized that these genes would share functions in pollen development similar to those of PIRL1 and PIRL9. Furthermore, it was hypothesized that PIRL2 and PIRL3 would also show redundancy with one another and with PIRL1 and PIRL9. In order to test these hypotheses, pollen from T-DNA knockout plant lines with single, double, and triple loss-of-function mutations in pirl2, pirl3, and pirl1 and/or pirl9 was assessed for viability and morphology using Alexander’s stain and scanning electron microscopy. Additionally, a pilot experiment to assess differential vulnerability to heat stress in these mutants was undertaken. The results suggest that these four related genes have overlapping and unequally redundant roles in pollen development. This may reflect the evolutionary history of these genes, which are derived from ancient duplication events.