An underground tale: contribution of microbial activity to plant iron acquisition

Iron (Fe) is an essen­tial nutri­ent for plants, and it serves as a cofactor for a wide vari­ety of cel­lu­lar pro­cesses, such as oxy­gen trans­port, cel­lu­lar res­pir­a­tion, chloro­phyll bio­syn­thesis, thylakoid bio­gen­esis and chloro­plast devel­op­ment. However, the Fe bioavail­ab­il­ity in well-aerated soils is often severely lim­ited, par­tic­u­larly in cal­careous soils, which occupy 30 % of the Earth’s sur­face. Hence, Fe-deficiency-induced chlorosis is a ser­i­ous prob­lem lead­ing to yield loss and reduced qual­ity in agri­cul­tural pro­duc­tion. Fe defi­ciency in plants is also closely related to the pre­val­ence of Fe-deficiency-induced anaemia in humans.

Plants have evolved at least two mech­an­isms favour­ing effi­cient acquis­i­tion of Fe. Strategy I, which occurs in non-graminaceous plants, relies on acid­i­fic­a­tion of the rhizo­sphere to increase the sol­u­bil­ity of fer­ric Fe com­pounds through pro­ton extru­sion, trans-plasma mem­brane elec­tron trans­fer to reduce Fe to its more sol­uble fer­rous form via fer­ric che­late reductase (FRO2) and trans­port of Fe into root cells by iron-regulated trans­porter 1. Strategy II, which is util­ized by the Gramineae, relies on extru­sion of mugineic acid fam­ily phytos­iderophores (MAs) via efflux trans­porter of MAs (e.g. TOM1) to sol­u­bil­ize Fe in the rhizo­sphere, and sub­sequent trans­port of the Fe(III)–phytosiderophore com­plex across the plasma mem­brane of the root epi­dermal cell via yel­low stripe1 trans­porter 1.

These two strategies have been thought to ensure nor­mal growth for many so-called ‘Fe-efficient’ plants under Fe-limited con­di­tions. In the last dec­ade, how­ever, sev­eral lines of evid­ence have shown that these strategies alone are insuf­fi­cient to pre­vent plants from suf­fer­ing Fe defi­ciency in Fe-limited soils. How soil micro-organisms pro­mote plant Fe acquis­i­tion is still largely unknown. Nevertheless, research­ers have made great efforts to uncover this inter­est­ing and import­ant under­ground mech­an­ism in recent dec­ades and have obtained many valu­able clues. Based on these clues, this review dis­cusses the pos­sible mech­an­isms for soil micro-organism pro­mo­tion of plant Fe acquisition.

Contribution of microbial activity to plant iron acquisition


Jin, C.W., Ye, Y.Q., & Zheng, S.J. An under­ground tale: con­tri­bu­tion of micro­bial activ­ity to plant iron acquis­i­tion via eco­lo­gical pro­cesses. (2014) Annals of Botany, 113(1), 7–18.
Iron (Fe) defi­ciency in crops is a world­wide agri­cul­tural prob­lem. Plants have evolved sev­eral strategies to enhance Fe acquis­i­tion, but increas­ing evid­ence has shown that the intrinsic plant-based strategies alone are insuf­fi­cient to avoid Fe defi­ciency in Fe-limited soils. Soil micro-organisms also play a crit­ical role in plant Fe acquis­i­tion; how­ever, the mech­an­isms behind their pro­mo­tion of Fe acquis­i­tion remain largely unknown.
This review focuses on the pos­sible mech­an­isms under­ly­ing the pro­mo­tion of plant Fe acquis­i­tion by soil micro-organisms.


AJ Cann. ORCID 0000-0002-9014-3720

Alan Cann is a Senior Lecturer in the School of Biological Sciences at the University of Leicester and formerly Internet Consulting Editor for AoB.