LISR28 Is Involved in Pollen Germination by Affecting Filamentous Actin Dynamics

Alternative splicing plays important roles in gene regulation and contributes to protein complexity. Previous studies suggest that alternative splicing exists in members of the villin/gelsolin/fragmin superfamily. In this study, a ser- ine/argine-rich （SR） protein cDNA with 28kDa protein （LISR28） was isolated from a lily （Lilium Iongiflorum） expression library. Protein domain analysis showed that LISR28 had similar structures to Arabidopsis SR45 （AtSR45）, and LISR28 could complement the phenotype of loss of AtSR45 function. Therefore, overexpression of LISR28 and AtSR45 mutant （atsr45-1） were used in the following experiments. Overexpression of LISR28 in Arabidopsis completely inhibited pollen germina- tion. In contrast, the pollen germination of atsr45-1 was earlier than that of wild-type. In addition, pollen of atsr45-1 contained less F-actin at the corresponding hydration stage during pollen germination compared to that of wild-type. Alternative splicing analysis showed that Arabidopsis villinl （AtVLN1） transcript encoding the full-length protein was increased, and that encoding the truncated protein was decreased in atst45-1. Moreover, the mRNA expression level of other actin-binding proteins （ABPs） abundant in Arabidopsis pollen was also changed in atsr45-1. In conclusion, we hypothesize that LISR28 alters F-actin dynamics probably through its alternative splicing activities to affect directly or indirectly the alternative splicing of AtVLN1 and the expression of different ABPs, which then affects the pollen germination.