Abstract
Calcium plays an essential role in pollen tube tip growth. However, little is known concerning the molecular basis of the signaling pathways involved. Here, we identified Arabidopsis (Arabidopsis thaliana) CALCINEURIN B-LIKE PROTEIN-INTERACTING PROTEIN KINASE19 (CIPK19) as an important element to pollen tube growth through a functional survey for CIPK family members. The CIPK19 gene was specifically expressed in pollen grains and pollen tubes, and its overexpression induced severe loss of polarity in pollen tube growth. In the CIPK19 loss-of-function mutant, tube growth and polarity were significantly impaired, as demonstrated by both in vitro and in vivo pollen tube growth assays. Genetic analysis indicated that disruption of CIPK19 resulted in a male-specific transmission defect. Furthermore, loss of polarity induced by CIPK19 overexpression was associated with elevated cytosolic Ca2+ throughout the bulging tip, whereas LaCl3, a Ca2+ influx blocker, rescued CIPK19 overexpression-induced growth inhibition. Our results suggest that CIPK19 may be involved in maintaining Ca2+ homeostasis through its potential function in the modulation of Ca2+ influx.
Highlights
Calcium plays an essential role in pollen tube tip growth
We demonstrated that Arabidopsis CIPK19, a CALCINEURIN B-LIKE PROTEIN-INTERACTING PROTEIN KINASEs (CIPKs) expressed in pollen grains and pollen tubes, functions in pollen tube tip growth, providing a new insight into the function of the CBLCIPK network in the control of growth polarity during pollen tube extension in fertilization
We were interested in the potential function of CIPKs in pollen biology and focused on those CIPK genes preferentially expressed in mature pollen grains
Summary
Calcium plays an essential role in pollen tube tip growth. little is known concerning the molecular basis of the signaling pathways involved. Fertilization is mediated by pollen tubes that extend directionally toward the ovule for sperm delivery (Krichevsky et al, 2007; Johnson, 2012) The formation of these elongated tubular structures is dependent on extreme polar growth (termed tip growth), in which cell expansion occurs exclusively in the very apical area (Yang, 2008; Rounds and Bezanilla, 2013). As this type of tip growth is amenable to genetic manipulation and cell biological analysis, the pollen tube is an excellent model system for the functional analysis of essential genes involved in polarity control and fertilization (Yang, 2008; Qin and Yang, 2011; Bloch and Yalovsky, 2013).
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