RESUMO
In flowering plants, pollen tubes are guided into ovules by multiple attractants from female gametophytes to release paired sperm cells for double fertilization. It has been well-established that Ca(2+) gradients in the pollen tube tips are essential for pollen tube guidance and that plasma membrane Ca(2+) channels in pollen tube tips are core components that regulate Ca(2+) gradients by mediating and regulating external Ca(2+) influx. Therefore, Ca(2+) channels are the core components for pollen tube guidance. However, there is still no genetic evidence for the identification of the putative Ca(2+) channels essential for pollen tube guidance. Here, we report that the point mutations R491Q or R578K in cyclic nucleotide-gated channel 18 (CNGC18) resulted in abnormal Ca(2+) gradients and strong pollen tube guidance defects by impairing the activation of CNGC18 in Arabidopsis. The pollen tube guidance defects of cngc18-17 (R491Q) and of the transfer DNA (T-DNA) insertion mutant cngc18-1 (+/-) were completely rescued by CNGC18. Furthermore, domain-swapping experiments showed that CNGC18's transmembrane domains are indispensable for pollen tube guidance. Additionally, we found that, among eight Ca(2+) channels (including six CNGCs and two glutamate receptor-like channels), CNGC18 was the only one essential for pollen tube guidance. Thus, CNGC18 is the long-sought essential Ca(2+) channel for pollen tube guidance in Arabidopsis.
Assuntos
Proteínas de Arabidopsis/fisiologia , Arabidopsis/fisiologia , Cálcio/metabolismo , Canais de Cátion Regulados por Nucleotídeos Cíclicos/fisiologia , Tubo Polínico/crescimento & desenvolvimento , Arabidopsis/genética , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Canais de Cálcio/fisiologia , GMP Cíclico/análogos & derivados , GMP Cíclico/farmacologia , Canais de Cátion Regulados por Nucleotídeos Cíclicos/química , Canais de Cátion Regulados por Nucleotídeos Cíclicos/deficiência , Canais de Cátion Regulados por Nucleotídeos Cíclicos/genética , Genes Reporter , Teste de Complementação Genética , Células HEK293 , Humanos , Potenciais da Membrana , Mutação de Sentido Incorreto , Óvulo Vegetal , Técnicas de Patch-Clamp , Infertilidade das Plantas/genética , Plantas Geneticamente Modificadas , Mutação Puntual , Estrutura Terciária de Proteína , Proteínas Recombinantes de Fusão/metabolismo , Sistemas do Segundo MensageiroRESUMO
The genetic identities of Ca2+ channels in root hair (RH) tips essential for constitutive RH growth have remained elusive for decades. Here, we report the identification and characterization of three cyclic nucleotide-gated channel (CNGC) family members, CNGC5, CNGC6, and CNGC9, as Ca2+ channels essential for constitutive RH growth in Arabidopsis. We found that the cngc5-1cngc6-2cngc9-1 triple mutant (designated shrh1) showed significantly shorter and branching RH phenotypes as compared with the wild type. The defective RH growth phenotype of shrh1 could be rescued by either the expression of CNGC5, CNGC6, or CNGC9 single gene or by the supply of high external Ca2+, but could not be rescued by external K+ supply. Cytosolic Ca2+ imaging and patch-clamp data in HEK293T cells showed that these three CNGCs all function as Ca2+-permeable channels. Cytosolic Ca2+ imaging in growing RHs further showed that the Ca2+ gradients and their oscillation in RH tips were dramatically attenuated in shrh1 compared with those in the wild type. Phenotypic analysis revealed that these three CNGCs are Ca2+ channels essential for constitutive RH growth, with different roles in RHs from the conditional player CNGC14. Moreover, we found that these three CNGCs are involved in auxin signaling in RHs. Taken together, our study identified CNGC5, CNGC6, and CNGC9 as three key Ca2+ channels essential for constitutive RH growth and auxin signaling in Arabidopsis.