Arabidopsis thaliana calmodulin-like protein CML24 regulates pollen tube growth by modulating the actin cytoskeleton and controlling the cytosolic Ca2+ concentration

Abstract

Cytosolic free calcium ([Ca(2+)]cyt), which is essential during pollen germination and pollen tube growth, can be sensed by calmodulin-like proteins (CMLs). The Arabidopsis thaliana genome encodes over 50 CMLs, the physiological role(s) of most of which are unknown. Here we show that the gene AtCML24 acts as a regulator of pollen germination and pollen tube extension, since the pollen produced by loss-of-function mutants germinated less rapidly than that of wild-type (WT) plants, the rate of pollen tube extension was slower, and the final length of the pollen tube was shorter. The [Ca(2+)]cyt within germinated pollen and extending pollen tubes produced by the cml24 mutant were higher than their equivalents in WT plants, and pollen tube extension was less sensitive to changes in external [K(+)] and [Ca(2+)]. The pollen and pollen tubes produced by cml24 mutants were characterized by a disorganized actin cytoskeleton and lowered sensitivity to the action of latrunculin B. The observations support an interaction between CML24 and [Ca(2+)]cyt and an involvement of CML24 in actin organization, thereby affecting pollen germination and pollen tube elongation.

Genome-Wide Identification and Analyses of Calmodulins and Calmodulin-like Proteins in Lotus japonicas

“…In tobacco, NtCaM13 was shown to be exclusively expressed in the root; however, 13 related CaM genes were expressed in almost all of the examined organs (Yamakawa et al, 2001). Steady state expression levels of CaM s have been reported to be modulated in different special phase of plant growth (Delk et al, 2005; Yang et al, 2014) as well as in response to external stimuli (Heo et al, 1999; Phean-o-pas et al, 2005; Gifford et al, 2013; Abbas et al, 2014). Therefore, the modulation of gene expression of a CaM isoform in specific organs allows for the possibility of functioning in a timely fashion.…”

“…CML 9, CML 24 and CML 37 have been reported to be induced by infection with the phytopathogenic bacterium Pseudomonas syringae and the herbivore Spodoptera littoralis (Delk et al, 2005; Leba et al, 2012; Scholz et al, 2014). AtCML 24 has been found to play a role in seed germination and to act as a positive regulator of pollen germination and pollen tube development (Delk et al, 2005; Yang et al, 2014). …”

iTRAQ-facilitated proteomic profiling of anthers from a photosensitive male sterile mutant and wild-type cotton (Gossypium hirsutum L.)

“…In plants, calcium (Ca 2+ ) is not only an essential plant nutrient element but is an intracellular secondary messenger. Ca 2+ plays an important role in plant growth and development, including pollen germination, and pollen tube growth and guidance [69][70][71]. These processes are crucial for male fertility.…”

“…Calmodulin-like proteins (CMLs), a plant specific family of Ca 2+ sensors, were reported to acts as a positive regulator of pollen germination and pollen tube development in Arabidopsis. The cml24 mutant displayed delayed pollen germination and inhibited pollen tube elongation, resulting in decreased seed set [69]. Other Ca 2+ binding proteins, like calreticulin [71] and annexin [72,73], participated in pollen development as well.…”

Calmodulin-like protein CML37 is a positive regulator of ABA during drought stress in Arabidopsis

“…For instance, CML24 can cause changes in abscisic acid (ABA) level during ion stress as well as changes in flowering time; it also regulates pollen tube growth by modulating the actin cytoskeleton and controlling the cytosolic Ca 2C concentration. [5][6][7] CML39 functions during early seedling establishment and activates defense responses.…”