MYB308-mediated transcriptional activation of plasma membrane H+-ATPase 6 promotes iron uptake in citrus

Abstract

Iron-deficiency chlorosis is a common nutritional disorder in crops grown on alkaline or calcareous soils. Although the acclimation mechanism to iron deficiency has been investigated, the genetic regulation of iron acquisition is still unclear. Here, by comparing iron uptake process between an iron-poor-soil-tolerant citrus species Zhique (ZQ) and an iron-poor-soil sensitive citrus species trifoliate orange (TO), we discovered the enhanced root H+ efflux is crucial for the tolerance to iron deficiency in ZQ. The H+ efflux is mainly regulated by a plasma membrane localized H+-ATPase HA6, the expression of which is up-regulated in plants grown in soil with low iron content and significantly higher in the roots of ZQ than TO. Overexpression of the HA6 gene in Arabidopsis thaliana aha2 mutant defective in iron uptake recovered the wild type phenotype. In parallel, overexpression of the HA6 gene in TO significantly increased iron content of plants. Moreover, an iron deficiency-induced transcription factor MYB308 was revealed to bind the promoter and activate the expression of HA6 in ZQ by yeast one-hybrid, electrophoretic mobility shift and dual-luciferase assays. Overexpression of MYB308 in ZQ roots significantly increased the expression level of HA6 gene. However, MYB308 can not bind or activate the HA6 promoter in TO due to the sequence variation of corresponding MYB308 binding motif. Together, we propose that the MYB308 could activate HA6 to promote root H+ efflux and iron uptake, and the distinctive MYB308-HA6 transcriptional module may be, at least in part, responsible for the iron deficiency tolerance in citrus.

Effects of Citric Acid and Humic-like Substances on Yield, Enzyme Activities, and Expression of Genes Involved in Iron Uptake in Tomato Plants

“…In that sense, the repression of LeHA1 (at 27 and 84 DAT) in leaf tissue under CA treatment and its high expression in root tissue under HLS treatment (at 49 DAT) suggest spatiotemporal expression patterns [14]. Such alterations would imply a modification of H + extrusion from the root tissue into the rhizospheric medium or cellular compartments [17,52]. In addition, humic complexes can induce an acid reaction in the soil by way of their diversity of functional groups [56], affecting LeHA1 expression.…”

“…In pea plants (Pisum sativum L.), in addition to higher FRO activity, overexpression of FRO1, IRT1, and HA1 was observed in the roots [15]. Similarly, in cucumber (Cucumis sativus L.) an increase in CsHA1 transcripts was reported in a higher proportion in the roots than in the leaves [16], whereas overexpression of HA6, which allowed for the outflow of H + from the root, was reported in a citrus species [17]. A key regulator in the activation of these mechanisms is FIT, which facilitates Fe uptake [18].…”

MxMPK6‐2‐mediated phosphorylation enhances the response of apple rootstocks to Fe deficiency by activating PM H+‐ATPase MxHA2

“…The transcriptional regulation of PM H + ‐ATPase also affects H + secretion ability of apple roots. For example, MYB308 can activate HA6 expression in Zhique, thus promoting root H + efflux and Fe uptake (Fan et al., 2022). MdbHLH104 directly binds to the promoter of MdAHA8 ( MxHA2 ) gene, thus regulating PM H + ‐ATPase activity and H + secretion (Zhao et al., 2016).…”

Transcription factors dealing with Iron‐deficiency stress in plants: focus on the bHLH transcription factor family

“…Subsequently, Wang et al (2018) also showed in apple that MdMYB58 could modulate Fe homeostasis by directly binding to the MdMATE43 promoter. Fan et al (2022) confirmed that MYB308 could activate HA6 to promote root H + efflux and Fe uptake in Citrus wilsonii , thus dealing with Fe deficiency stress.…”