In flowering plants, diverse attractants from female gametophytes guide pollen tube growth to ovules for double fertilization. It has been well established that a Ca²⁺ gradient in pollen tube tips is essential for pollen tube guidance, and plasma membrane Ca²⁺ channels in the pollen tube tips have been proposed as core components for pollen tube guidance by mediating and regulating external Ca²⁺ influx, and by consequently regulating the Ca²⁺ gradient in the pollen tube tips. However, there is still no genetic evidence for the identification of the putative Ca²⁺ channels essential for pollen tube guidance for decades.

A team led by Dr. Yong-Fei Wang, at the Institute of Plant Physiology and Ecology (SIPPE), Shanghai Institutes for Biological Sciences (SIBS), CAS found that a cyclic nucleotide-gated channel 18 (CNGC18) is the long-sought Ca²⁺ channel essential for pollen tube guidance in Arabidopsis. In this research, it was revealed that CNGC18, out of eight Ca²⁺ channels present in pollen tubes, played a vital role in pollen tube guidance in Arabidopsis. Either the point mutation R491Q or R578K in CNGC18 resulted in abnormal Ca²⁺ gradients and further led to strong pollen tube guidance defects and severe male sterility by impairing its activation by upstream activators. The pollen tube guidance defects of cngc18-17 (R491Q) and pollen tube transmission defects of cngc18-1 (+/-) were completely rescued by the expression of wild type CNGC18, but were not or only slightly rescued by the other five CNGCs. Further analysis found that the transmembrane domains of CNGC18 are essential for pollen tube guidance to ovules. These findings thus pave the way for unravelling the signaling pathway of pollen tube guidance in the future.

This work entitled “Cyclic nucleotide-gated channel 18 is an essential Ca²⁺ channel in pollen tube tips for pollen tube guidance to ovules in Arabidopsis” was published in Proc Natl Acad Sci USA on February 29, 2016.

CONTACT:
Wang Yong-Fei
Institute of Plant Physiology and Ecology,
Shanghai Institutes for Biological Sciences,
Chinese Academy of Sciences,
300 Fenglin Road, Shanghai 200032, China
Tel: +86-21-54924308
Email: wangyongfei@sibs.ac.cn

The R491Q and R578K point mutations in CNGC18 resulted in severe pollen tube growth defects whereas the T-DNA insertion mutations in the other seven Ca²⁺ channels had no pollen tube growth defects (Image provided by WANG Yong-Fei’s group).