RESUMEN
Aluminum (Al) toxicity poses a significant challenge for the yield improvement of chickpea, which is an economically important legume crop with high nutritional value in human diets. The genetic basis of Al-tolerance in chickpea remains unclear. Here, we assessed the Al-tolerance of 8 wild Cicer and one cultivated chickpea (PBA Pistol) accessions by measuring the root elongation in solution culture under control (0 µM Al3+) and Al treatments (15, 30 µM Al3+). Compared to PBA Pistol, the wild Cicer accessions displayed both tolerant and sensitive phenotypes, supporting wild Cicer as a potential genetic pool for Al-tolerance improvement. To identify potential genes related to Al-tolerance in chickpea, genome-wide screening of multidrug and toxic compound extrusion (MATE) encoding genes was performed. Fifty-six MATE genes were identified in total, which can be divided into 4 major phylogenetic groups. Four chickpea MATE genes (CaMATE1-4) were clustered with the previously characterized citrate transporters MtMATE66 and MtMATE69 in Medicago truncatula. Transcriptome data showed that CaMATE1-4 have diverse expression profiles, with CaMATE2 being root-specific. qRT-PCR analyses confirmed that CaMATE2 and CaMATE4 were highly expressed in root tips and were up-regulated upon Al treatment in all chickpea lines. Further measurement of carboxylic acids showed that malonic acid, instead of malate or citrate, is the major extruded acid by Cicer spp. root. Protein structural modeling analyses revealed that CaMATE2 has a divergent substrate-binding cavity from Arabidopsis AtFRD3, which may explain the different acid-secretion profile for chickpea. Pangenome survey showed that CaMATE1-4 have much higher genetic diversity in wild Cicer than that in cultivated chickpea. This first identification of CaMATE2 and CaMATE4 responsive to Al3+ treatment in Cicer paves the way for future functional characterization of MATE genes in Cicer spp., and to facilitate future design of gene-specific markers for Al-tolerant line selection in chickpea breeding programs.
RESUMEN
In many acidic soils, high concentrations of toxic Al3+ hamper plant growth by restricting root growth which in turn restricts water and nutrient absorption. Previous research showed variation among chickpea (Cicer arietinum L.) and wild Cicer species in root elongation at 15 µM Al or more, but effects on nutrient absorption have not been examined. The variation in nutrient uptake of two chickpea varieties (PBA HatTrick and PBA Striker) and two wild Cicer species (C. echinospermum (C. echi) and C. reticulatum (C. reti)) was determined in low pH (4.2) nutrient solution with increasing Al concentrations (0, 7.5, 15, 30 µM Al). While C. echi, PBA HatTrick and PBA Striker had thicker roots and more lateral roots compared to C. reti, C. reti had greater aluminium tolerance index (AlTI) at 15 and 30 µM Al. The C. echi had higher uptake of root and shoot Al (7.5, 15 and 30 µM Al), P and S (15 and 30 µM Al) while its uptake was marginally lower for Mg, Ca (all Al treatments) and K (15 and 30 µM Al). By contrast, C. reti contained higher shoot Ca concentration at 15 and 30 µM Al and it had lower root Al uptake. Manganese uptake by C. reti roots and shoots were high enough to induce moderate Mn toxicity at 0 and 7.5 µM Al. Therefore, in response to Al toxicity, C. reti maintained greater AlTI and restricted Al uptake while increasing Ca uptake.