MIKC*-type MADS transcription factors control JINGUBANG expression and the degree of pollen dormancy in Arabidopsis

Abstract

While pollen dormancy has been proposed to play a necessary role in sexual reproduction, it remains poorly understood. Here, we used traditional pollen germination assays to characterize dormancy. Our results underscore variation in the degree of dormancy between individual pollen grains. In addition, we provide evidence that JINGUBANG (JGB), previously defined as a negative regulator of pollen germination in Arabidopsis (Arabidopsis thaliana), is responsible for the uneven degrees of pollen dormancy, as asynchronous pollen germination in vitro reflected varied expression levels of JGB. We identified five cis-acting elements, including four CArG-boxes and the previously uncharacterized element ERE7, as essential for the initiation and enhancement of JGB expression. A 10-bp sequence between CArG-box 3 and ERE7, likely the result of an inverse DNA loop formed between CArG-box 3 and CArG-box 4, was required for robust gene expression. In addition, the pollen-specific AtMIKC*-type MADS transcription factors AGAMOUS-LIKE 30 (AGL30), AGL65, AGL66, AGL94, and AGL104 activated JGB transcription. Notably, the transactivation levels differed among the obligate AtMIKC* heterodimers tested. Our results indicate that distinct AtMIKC* complexes formed in individual pollen grains direct pollen dormancy to uneven degrees, which is likely an adaptive trait that ensures broader pollen dispersal under adverse environmental conditions.