Plant-associated methylobacteria as co-evolved phytosymbionts: a hypothesis

Area of Science:

• Plant-microbe interactions
• Microbial metabolism
• Bryophyte biology

Background:

• Growing plant cells release methanol via pectin metabolism.
• Epiphytic Methylobacterium bacteria can use methanol as their sole carbon and energy source.

Purpose of the Study:

• To investigate the interaction between Methylobacterium and various plant life stages.
• To determine if Methylobacterium influences plant growth and development.

Main Methods:

• Experiments were conducted using gnotobiotic (germ-free) angiosperm sporophytes (sunflower, maize) and bryophyte gametophytes (moss, liverworts).
• The effects of Methylobacterium colonization on plant organ development were observed.

Main Results:

• Methylobacterium did not stimulate growth in angiosperms.
• Significant enhancement of organ development was observed in moss protonemata and liverwort thalli.
• Methylobacteria secrete plant hormones like cytokinins and auxin.

Conclusions:

• A symbiotic relationship is proposed between methanol-consuming Methylobacterium and haploid gametophytes of bryophytes.
• This symbiosis enhances gametophyte growth, survival, and reproduction (fitness).
• The symbiosis is specific to haploid gametophytes and not observed in diploid sporophytes of higher plants.