Ectopic expression of a thaumatin-like protein impairs the timely deposition and dissolution of callose during microsporogenesis, leading to microspore death and male sterility in Arabidopsis.

Key message: Two pollen-preferential thaumatin-like proteins show both common and distinctive expression profiles. Precocious expression of one of them drastically disturbs timely deposition and dissolution of callose during microsporogenesis, leading to microspore death. Thaumatin-like proteins (TLPs), members of the pathogenesis-related protein family 5 (PR-5), are involved in plant defenses against biotic and abiotic stresses through antifungal activity and enhanced tolerance. Accordingly, studies on TLPs have focused on their responses to various pathogens and stresses and on engineering agronomically valuable crops that can be cultivated in suboptimal environments. On the other hand, the role of TLP members in plant development and their genetic regulation remains largely unexplored. Recently, we reported that the generative cell internalization after pollen mitosis I, an essential pollen patterning step for the nonmotile sperm cell delivery through a pollen tube, depends on STICKY GENERATIVE CELL which suppresses callose deposition in the nascent generative cell and interacts with a germline cell preferential GCTLP1 in Arabidopsis. Here, we additionally identified GCTLP2 which is similarly expressed in the germline cells. We generated various transgenic lines and examined their expressions and phenotypes to elucidate GCTLP functions during pollen development. Expression profiles suggest two GCTLP proteins may have common but also distinctive roles during pollen development. Importantly, ectopic expression analyses show that precocious expression of GCTLP2 severely disturbs the timely deposition and degradation of callose during microsporogenesis which is essential to produce viable microspores. Therefore, our study broadens the knowledge of TLP function and callose regulation for successful pollen development in Arabidopsis.