Delayed callose degradation restores the fertility of multiple P/TGMS lines in Arabidopsis.

Photoperiod/temperature-sensitive genic male sterility (P/TGMS) is widely applied for improving crop production. Previous investigations using the reversible male sterile (rvms) mutant showed that slow development is a general mechanism for restoring fertility to P/TGMS lines in Arabidopsis. In this work, we isolated a restorer of rvms-2 (res3), as the male sterility of rvms-2 was rescued by res3. Phenotype analysis and molecular cloning show that a point mutation in UPEX1 l in res3 leads to delayed secretion of callase A6 from the tapetum to the locule and tetrad callose wall degradation. Electrophoretic mobility shift assay and chromatin immunoprecipitation analysis demonstrated that the tapetal transcription factor ABORTED MICROSPORES directly regulates UPEX1 expression, revealing a pathway for tapetum secretory function. Early degradation of the callose wall in the transgenic line eliminated the fertility restoration effect of res3. The fertility of multiple known P/TGMS lines with pollen wall defects was also restored by res3. We propose that the remnant callose wall may broadly compensate for the pollen wall defects of P/TGMS lines by providing protection for pollen formation. A cellular mechanism is proposed to explain how slow development restores the fertility of P/TGMS lines in Arabidopsis.