Redundant mechanisms in division plane positioning

Kinesin-12 POK2 polarization is a prerequisite for a fully functional division site and aids cell plate positioning

Division plane positioning in plants relies on the remarkably accurate selection of the cortical division zone (CDZ), earmarked by the preprophase band of microtubules. The PHRAGMOPLAST ORIENTING KINESIN 1 and 2 (POK1/2) play pivotal roles in CDZ maintenance in mitosis and guide the approaching phragmoplast during cytokinesis. Our knowledge regarding the mechanism of POK recruitment and subsequent maintenance is hitherto limited. Here, we report that POK2 arrives at the preprophase band utilizing a secondary microtubule-binding site within its carboxy-terminus. Effective tethering to the plasma membrane is achieved through non-specific electrostatic interactions with phospholipids. Reaching the cortex via premitotic cortical microtubules emerges as a prerequisite for POK2 polarization, as the order and the density of prophase microtubules become particularly relevant in the preprophase band-compromised mutant trm678. POK2 binding to cortical microtubules templates its future position at the cortex and appears critical for adequate division site setup and consequently tissue architecture.

The virulence contribution of the CFEM family genes of Beauveria bassiana is closely influenced by the external iron environment

The common in fungal extracellular membrane (CFEM) domain proteins represent characteristic fungal extracellular membrane proteins. The entomopathogenic fungus Beauveria bassiana contains 12 CFEM domain proteins involved in the generation of iron hunger response. However, many BbCFEM genes that infect insects do not promote fungal virulence. In this study, we systematically assessed the role of the BbCFEM family in fungal virulence under moderate iron concentrations and severe iron starvation (0.4 mM BPS) induced by body wall infection and injection infection. The results showed that the BbCFEM family members have different functions based on virulence, which is directly affected by external iron levels. Quantitative real-time reverse-transcription polymerase chain reaction preliminarily demonstrated that deletion of BbCFEM family genes significantly increased the expression levels of other family members. The increased expression levels compensated for the gene damage induced by the deletion of BbMFEM genes. In addition, the results showed that the BbCFEM gene participates in the initiation of fungal responses to cell wall stress and oxidative stress. These findings reveal the evolutionary strategies employed by pathogenic fungi to adapt to the environment and population reproduction. This study expands our understanding of the mechanism of this gene family of entomopathogenic fungi in infecting pests.

IMPORTANCE

The common in fungal extracellular membrane (CFEM) domain is a fungal extracellular membrane protein that can trap heme, which assists in fungal infection and colonization. Beauveria bassiana is an entomopathogenic fungus that is widely used to control pests. We systematically assessed the contribution of the BbCFEM family to B. bassiana's virulence under severe iron starvation and B. bassiana's growth and stress resistance under moderate iron levels. We found that the BbCFEM family members have different functions based on virulence with severe iron starvation, which also plays an important role in fungal responses to cell wall stress and oxidative stress. This study provides new insights into the genetic families of entomopathogenic fungi and the mechanisms by which they infect pests.

Spatiotemporal regulation of plant cell division

Plant morphogenesis largely depends on the orientation and rate of cell division and elongation, and their coordination at all levels of organization. Despite recent progresses in the comprehension of pathways controlling division plane determination in plant cells, many pieces are missing to the puzzle. For example, we have a partial comprehension of formation, function and evolutionary significance of the preprophase band, a plant-specific cytoskeletal array involved in premitotic setup of the division plane, as well as the role of the nucleus and its connection to the preprophase band of microtubules. Likewise, several modeling studies point to a strong relationship between cell shape and division geometry, but the emergence of such geometric rules from the molecular and cellular pathways at play are still obscure. Yet, recent imaging technologies and genetic tools hold a lot of promise to tackle these challenges and to revisit old questions with unprecedented resolution in space and time.