Maize drought protection by Azospirillum argentinense Az19 requires bacterial trehalose accumulation

Area of Science:

• Microbiology
• Plant Science
• Biochemistry

Background:

• Azospirillum argentinense Az19 is a plant growth-promoting bacterium known for drought protection in maize.
• Trehalose is a key osmoprotectant in bacteria, but its specific role in Az19's performance is not fully understood.

Purpose of the Study:

• To investigate the role of trehalose metabolism in Azospirillum argentinense Az19's stress tolerance and plant growth-promoting capabilities.
• To determine if trehalose is essential for Az19's protective effects on maize under drought conditions.

Main Methods:

• A trehalase-deficient mutant (Az19F) was created by constitutively expressing the treF gene.
• The mutant's physiological responses to various stresses (salt, osmotic, UV) and normal conditions were assessed.
• The ability of both wild-type and mutant strains to colonize maize roots and promote plant growth under normal and drought conditions was evaluated.

Main Results:

• The trehalose-deficient Az19F mutant exhibited reduced tolerance to salt, osmotic, and UV stress, with increased reactive oxygen species.
• Az19F showed altered physiology, including enhanced biofilm formation and motility, but decreased auxin secretion.
• While root colonization was unaffected, Az19F failed to promote maize growth under drought, unlike the wild-type Az19, and induced a stronger oxidative response in plants.

Conclusions:

• Trehalose metabolism in Azospirillum argentinense Az19 is crucial not only for stress tolerance but also for normal bacterial physiology.
• Trehalose plays a significant role in the bacterium's ability to promote maize growth and protect it from drought stress.
• The findings highlight trehalose as a key factor in the symbiotic relationship between Azospirillum and maize, particularly under adverse environmental conditions.