INDUCER OF CBF EXPRESSION 1 is a male fertility regulator impacting anther dehydration in Arabidopsis

Abstract

INDUCER OF CBF EXPRESSION 1 (ICE1) encodes a MYC-like basic helix-loop-helix (bHLH) transcription factor playing a critical role in plant responses to chilling and freezing stresses and leaf stomata development. However, no information connecting ICE1 and reproductive development has been reported. In this study, we show that ICE1 controls plant male fertility via impacting anther dehydration. The loss-of-function mutation in ICE1 gene in Arabidopsis caused anther indehiscence and decreased pollen viability as well as germination rate. Further analysis revealed that the anthers in the mutant of ICE1 ( ice1-2) had the structure of stomium, though the epidermis did not shrink to dehisce. The anther indehiscence and influenced pollen viability as well as germination in ice1-2 were due to abnormal anther dehydration, for most of anthers dehisced with drought treatment and pollen grains from those dehydrated anthers had similar viability and germination rates compared with wild type. Accordingly, the sterility of ice1-2 could be rescued by ambient dehydration treatments. Likewise, the stomatal differentiation of ice1-2 anther epidermis was disrupted in a different manner compared with that in leaves. ICE1 specifically bound to MYC-recognition elements in the promoter of FAMA, a key regulator of guard cell differentiation, to activate FAMA expression. Transcriptome profiling in the anther tissues further exhibited ICE1-modulated genes associated with water transport and ion exchange in the anther. Together, this work reveals the key role of ICE1 in male fertility control and establishes a regulatory network mediated by ICE1 for stomata development and water movement in the anther.

Author summary

INDUCER OF CBF EXPRESSION 1 (ICE1) is a basic helix-loop-helix transcription factor playing multiple roles in Arabidopsis. It was initially identified as the activator of C-Repeat Binding Factor 3 (CBF3), a core modulator triggering cold acclimation. ICE1 also activates Flowering Locus C (FLC), a major repressor of floral transition, to delay flowering under fluctuating environmental stimuli. In normal conditions, ICE1 participates in control of stomatal development in leaves and endosperm breakdown in seeds. Here we describe a role of ICE1 in male fertility development of Arabidopsis. We provide evidence that ICE1 controls stomatal differentiation in the anther epidermis and thereby anther dehiscence and pollen viability as well as germination. Consequently, fertility of ice1 mutant can be rescued by ambient dehydration. ICE1 regulates FAMA, one key regulator of guard cell differentiation, through direct binding to MYC-recognition elements in FAMA promoter. Moreover, we perform transcriptomic analysis using anther tissues and identify ICE1-regulated genes involved in water transport. These findings reveal a novel role of ICE1 in male fertility regulation through affecting water movement in the anther, which deepens our understanding of coordination between plant development and stress response, and potentially contributes to the pollination controls in crop breeding.