MCA1 and MCA2 That Mediate Ca2+ Uptake Have Distinct and Overlapping Roles in Arabidopsis

Abstract

Ca2+ is important for plant growth and development as a nutrient and a second messenger. However, the molecular nature and roles of Ca 2+ -permeable channels or transporters involved in Ca 2+ uptake in roots are largely unknown. We recently identified a candidate for the Ca 2+ -permeable mechanosensitive channel in Arabidopsis (Arabidopsis thaliana), named MCA1. Here, we investigated the only paralog of MCA1 in Arabidopsis, MCA2. cDNA of MCA2 complemented a Ca 2+ uptake deficiency in yeast cells lacking a Ca 2+ channel composed of Mid1 and Cch1. Reverse transcription polymerase chain reaction analysis indicated that MCA2 was expressed in leaves, flowers, roots, siliques, and stems, and histochemical observation showed that an MCA2 promoter::GUS fusion reporter gene was universally expressed in 10-d-old seedlings with some exceptions: it was relatively highly expressed in vascular tissues and undetectable in the cap and the elongation zone of the primary root. mca2-null plants were normal in growth and morphology. In addition, the primary root of mca2-null seedlings was able to normally sense the hardness of agar medium, unlike that of mca1-null or mca1-null mca2-null seedlings, as revealed by the two-phase agar method. Ca 2+ uptake activity was lower in the roots of mca2-null plants than those of wild-type plants. Finally, growth of mca1-null mca2-null plants was more retarded at a high concentration of Mg 2+ added to medium compared with that of mca1-null and mca2-null single mutants and wild-type plants. These results suggest that the MCA2 protein has a distinct role in Ca 2+ uptake in roots and an overlapping role with MCA1 in plant growth.Calcium ion (Ca 2+

Expression of Arabidopsis MCA1 enhanced mechanosensitive channel activity in theXenopus laevisoocyte plasma membrane

“…Similar results were obtained in oocytes expressing MCA2, a homolog of MCA1. 16 The alteration in the amplitude of the pressure dependent inward current was not obtained in control oocytes expressing an inward-rectifying K + channel KAT1 of A. thaliana (Fig. 2C).…”

“…Most recently, homologous genes in tobacco and rice, NtMCA1, NtMCA2 and OsMCA1, respectively, were identified; they are localized in the plasma membrane, channel Ca 2+ , and may have potential roles in cell proliferation. 16,17 However, direct evidence for mechanical stress-dependent activation of MCA proteins is still lacking.…”

“…As another group of genes encoding putative mechanosensitive channels in Arabidopsis, MCA1 (mid1-complementing activity 1) and its paralog, MCA2, were isolated via functional complementation of the conditional lethality of a yeast mid1 (mating pheromone-induced death 1) mutant lacking a Ca 2+ channel component that is activated by membrane stretch when expressed in mammalian cells. 15,16 The subcellular localization of GFP-labeled-MCA1 and -MCA2 in Arabidopsis root cells has shown that both proteins are localized in the plasma membrane. 15,16 A knockout mutant of MCA1 shows a unique phenotype, incapability of penetration from softer to harder agar medium, suggesting that MCA1 is required for sensing the hardness of soil.…”

“…15,16 The subcellular localization of GFP-labeled-MCA1 and -MCA2 in Arabidopsis root cells has shown that both proteins are localized in the plasma membrane. 15,16 A knockout mutant of MCA1 shows a unique phenotype, incapability of penetration from softer to harder agar medium, suggesting that MCA1 is required for sensing the hardness of soil. 15 An aequorin-based analysis of [Ca 2+ ] c in the seedlings of an MCA1 overexpressing Arabidopsis line has revealed that MCA1 participates in Ca 2+ -influx in response to rESEArCH PAPEr MCA1 was microinjected into defolliculated oocytes, and the electrophysiological characteristics of MCA1-expressing oocytes were examined.…”

Comparative transcriptomics reveals patterns of selection in domesticated and wild tomato

“…Many of these genes have not been characterized in tomato, but annotated genes included the tomato homolog of the Arabidopsis thaliana ARGONAUTE 2 and the known tomato-resistance gene immunity to fusarium wilt-2C4 (24,25), consistent with rapid evolution of protein sequences in response to pathogen pressure. Homologs of the aluminum transporter ALUMINUM SENSITIVE 1 and the calcium uptake transporter MID1-COMPLEMENTING ACTIVITY 1 also showed significantly elevated dN/dS pointing to positive selection in response to abiotic factors, such as soil chemistry (26,27). This second set of genes is particularly interesting considering the high salt tolerance observed in wild tomato relatives (28).…”