Mg2+ uptake QTLs

Hannah Itell and Eric Sawyer

Biological roles for Mg2+

● chlorophyll

● common cofactor (RNA pol, kinases, ATPases, …)

● most Mg2+ is not free in cytoplasm (ATP/nucleotide-chelated or in organelles) < 2 mM

chlorophyll a

Biological roles for Mg2+

● vacuole: 3-13 mM Mg2+

● highest [Mg2+]: thylakoid lumen (30-50 mM), but importers unknown!

● Mg2+ uptake hindered by acidic soils

● Mg2+ deficiency can lead to Al3+ toxicity; transporter competition

chlorophyll a

Signs of Mg2+ deficiency● chlorophyll breakdown

● impaired sugar mobilization

● reduced growth, particularly roots

Mg2+ biochemistryA. Cation channelsB. MGTC. MHXD. Slow activating vacuolar

channels (SVs)E. MGT5F. MGT10 and FACCs (G)

Bose et al. (2011)

1. Mg2+ channels (plasma membrane)● Hyperpolarization-activated● Depolarization-activated● Voltage-independent● Cyclic nucleotide-activated● Non-selective ion channels

● AtCNGC10 (A. thaliana): mediates Mg2+ mobilization through the plant

2. Mg2+ Carrier Proteins (MGTs)

● Magnesium (Mg2+) Transport Family

● AtMGT1, 5, 7a, 9, 10

● Vary in affinity and sensitivity to Al3+

Plasma Membrane Mitochondria Chloroplast

AtCNGC10 AtMGT family

Candidate gene BLAST results

C639,822,476 bp

QTL: 7,628,656 +/- 1 Mbp

IGB

No hits :(

C841,758,685 bp

QTL: 40,141,039 +/- 1 Mbp

IGBCation/Calcium Exchanger @ 39,717,422

Cation/H+ Exchanger @ 39,945,936

Cation/H+ Exchanger @ 39,950,514

Cation/H+ Antiporter @ 40,277,578

C546,902,585 bp

QTL: 44,023,210 +/- 1 Mbp

IGB

Heavy metal transport/detoxification domain-containing protein @ 43,792,027

Calmodulin-like protein @ 43,857,726

Metallothionein-like protein @ 43,295,039 Golgi-assoc. cation binding protein

Calcium transporting ATPase @ 43,882,735 Similar to AT1G07810 cation transporter

Heavy metal transport/detoxification superfamily protein @ 44,678,689

C748,366,697 bp

QTL: 35,691,416 +/- 1 Mbp

QTL: 39,973,848 +/- 1 Mbp

IGBV-type proton ATPase subunit d2 @ 35,255,037

Caleosin-related family protein @ 35,570,359

Heavy metal transport/detoxification superfamily protein @ 36,474,786

Cation transport regulator-like protein @ 36,606,567

Major facilitator superfamily protein @ 35,825,037 small solute transporter

V-type proton ATPase 16 kDa proteolipid subunit c1/c3/c5 @ 39,793,003

Heavy metal transport/detoxification superfamily protein @ 40,122,906

Cation proton exchanger @ 39,509,003

Vacuolar cation/proton exchanger @ 39,433,988 & 39,437,869

C453,719,093 bp

QTL: 40,219,218 +/- 1 Mbp

IGB

Magnesium Transporter (Predicted) @ 39,807,316

Mitochondrial Carrier Protein @ 40,692,677

Conclusions● No candidate gene BLAST hits within 1 Mbp of QTL

● CNGC10 and MGT family hit every QTL +/- 10 Mbp

● IGB search within 1 Mbp of QTLs foundo vacuolar pumps/transporters

o heavy metal transporters (Al3+-Mg2+ antagonism?)

o Ca2+, Mg2+, and general cation transporters and binding proteins

ReferencesBose, J. et al. 2010. Role of magnesium in alleviation of aluminium toxicity in

plants. Journal of Experimental Botany 62: 2251-2264.

Hermans, C. et al. 2010. Systems analysis of the responses to long-term magnesium deficiency and restoration in Arabidopsis thaliana. New Phytologist 187: 132-144.

Perez, V. et al. 2008. Homeostatic control of slow vacuolar channels by luminal cations and evaluation of the channel-mediated tonoplast Ca2+ fluxes in situ. Journal of Experimental Botany 59: 3845-3855.