Authors:
Hirotsuna Yamada | Graduate School of Integrated Sciences for Life/ Hiroshima University | Japan
Lydia Ratna Bunthara | Graduate School of Integrated Sciences for Life/ Hiroshima University | Japan
Akira Tanaka | Faculty of Agriculture/ Saga University | Japan
Takuro Kohama | School of Integrated Arts and Sciences/ | Japan
Dr. Hayato Maruyama | School of Agriculture/ Hokkaido University | Japan
Dr. Wakana Tanaka | Graduate School of Integrated Sciences for Life/ Hiroshima University | Japan
Dr. Sho Nishida | Faculty of Agriculture/ Saga University, The United Graduate School of Agricultural Sciences | Japan
Dr. Takayuki Sasaki | Institute of Plant Science and Resources/ Okayama University | Japan
Prof. Dr. Jun Wasaki | Graduate School of Integrated Sciences for Life/ Hiroshima University, School of Integrated Arts and Sciences/ Hiroshima University, Seto Inland Sea Carbon Neutral Research Center, Higashi-Hiroshima | Japan
In Western Australia, many Proteaceae species exhibit a distinctive root morphology known as “cluster roots” (CRs) in response to Phosphorus (P) deficiency. Multiple studies have highlighted the efficient P absorption capabilities of CR-forming species, underscoring their remarkable capacity for carboxylates release. However, the molecular mechanisms underlying this phenomenon remain poorly understood. Therefore, our research focused on investigating malate release activities and identified a novel gene related to malate transport in Hakea laurina.
By determining malate exudation rates across various developmental stages of CRs in H. laurina as a physiological trait, malate release was higher in mature CRs than the other stages. Through RNA-Seq analysis, we identified a transcript encoding an aluminum-activated malate transporter (ALMT) family protein that was significantly abundant in mature CRs. This transcript was subsequently named HalALMT1. Both electrophysiological assays of HalALMT1 expressed in Xenopus oocytes using the two-electrode voltage clamp method and measurements of malate exudation rates in Arabidopsis overexpressing HalALMT1 confirmed its capacity to release malate, which was further activated by exposure to Al3+. Additionally, HalALMT1-overexpressing atalmt1 mutants showed longer roots than atalmt1 mutant under AlCl3 treatments, suggesting HalALMT1 contributes to alleviating Al3+ toxicity.
In situ hybridization of HalALMT1 revealed its expression primarily in the cortex, approximately 500 µm away from the tips, rather than the rootlet tips. This suggests that HalALMT1 plays a role in facilitating P absorption apoplastically from the soil adhering to CRs.