Genome-wide identification and transcriptional analyses of MATE transporter genes in root tips of wild Cicer spp. under aluminium stress

Chickpea is an economically important legume crop with high nutritional value in human diets. Aluminium-toxicity poses a significant challenge for the yield improvement of this increasingly popular crop in acidic soils. The wild progenitors of chickpea may provide a more diverse gene pool for Al-tolerance in chickpea breeding. However, the genetic basis of Al-tolerance in chickpea and its wild relatives remains largely unknown. Here, we assessed the Al-tolerance of six selected wild Cicer accessions by measuring the root elongation in solution culture under control (0 uM Al3+) and Al-treatment (30 uM Al3+) conditions. Al-treatment significantly reduced the root elongation in all target lines compared to the control condition after 2-days9 growth. However, the relative reduction of root elongation in different lines varied greatly: 3 lines still retained significant root growth under Al-treatment, whilst another 2 lines displayed no root growth at all. We performed genome-wide identification of multidrug and toxic compound extrusion (MATE) encoding genes in the Cicer genome. A total of 56 annotated MATE genes were identified, which divided into 4 major phylogeny groups (G1-4). Four homologues to lupin LaMATE (> 50% aa identity; named CaMATE1-4) were clustered with previously characterised MATEs related to Al-tolerance in various other plants. qRT-PCR showed that CaMATE2 transcription in root tips was significantly up-regulated upon Al-treatment in all target lines, whilst CaMATE1 was up-regulated in all lines except Bari2_074 and Deste_064, which coincided with the lines displaying no root growth under Al-treatment. Transcriptional profiling in five Cicer tissues revealed that CaMATE1 is specifically transcribed in the root tissue, further supporting its role in Al-detoxification in roots. This first identification of MATE-encoding genes associated with Al-tolerance in Cicer paves the ways 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.