CIK Receptor Kinases Determine Cell Fate Specification During Early Anther Development In Arabidopsis

Anthers,the male part of flowering plants,can produce and release pollen grains that containing sperm cells,playing important roles in the process of plant sexual reproduction.Appropriate cell division and differentiation are necessary for normal anther development.BARELY ANY MERISTEM 1/2(BAM1/2)and RECEPTOR-LIKE PROTEIN KINASE 2(RPK2),two groups of leucine-rich repeat receptor-like protein kinases(LRR-RLKs),are required for early anther cell specification.However,little is known about the molecular mechanisms underlying these two RLK-mediated signaling pathways.Here,we show that CLAVATA3 INSENSITIVE RECEPTOR KINASES(CIKs),a group of novel co-receptor protein kinase controlling stem cell homeostasis,play essential roles in BAM1/2-and RPK2-regulated early anther development in Arabidopsis thaliana.The archesporial cells of cik1/2/3 triple and cik1/2/3/4 quadruple mutant anthers perform anticlinal division instead of periclinal division.Defective cell division and specification of the primary and inner secondary parietal cells occur in these mutant anthers.The disordered divisions and specifications of anther wall cells finally result in excess microsporocytes and a lack of one to three parietal cell layers in mutant anthers,resembling rpk2 or bam1/2 mutant anthers.Genetic analysis proved that CIKs function in the same genetic pathway with BAM1/2 and RPK2.Biochemical assays showed that CIKs can interact with and be phosphorylated by BAM1/2 and RPK2.In conclusion,CIKs may function as co-receptors of BAM1/2 and RPK2 to regulate archesporial cell division and determine the specification of anther parietal cells.