Sodium (Na+) and potassium (K+) homeostasis is essential for plant survival in saline soils. A member of the High-Affinity K+ Transporter (HKT) family in rice (Oryza sativa), OsHKT1;1, is a vital regulator of Na+ exclusion from shoots and is bound by a MYB transcription factor (OsMYBc). Here, we generated transgenic rice lines in the oshkt1;1 mutant background for genetic complementation using genomic OsHKT1;1 containing a native (Com) or mutated (mCom) promoter that cannot be bound by OsMYBc. In contrast to wild-type (WT) or Com lines, the mCom lines were not able to recover the salt-sensitive phenotype of oshkt1;1. The OsMYBc-overexpressing plants were more tolerant to salt stress than WT plants. A yeast two-hybrid screen using the OsMYBc N-terminus as bait identified a rice MYBc stress-related RING finger protein (OsMSRFP). OsMSRFP is an active E3 ligase that ubiquitinated OsMYBc in vitro and mediated 26S proteasome-mediated degradation of OsMYBc under semi-in vitro and in vivo conditions. OsMSRFP attenuated OsMYBc-mediated OsHKT1;1 expression, and knockout of OsMSRFP led to rice salt tolerance. These findings uncover a regulatory mechanism of salt response that fine-tunes OsHKT1;1 transcription by ubiquitination of OsMYBc.
鈉離子和鉀離子平衡對(duì)于植物在鹽逆境條件下的生存至關(guān)重要。OsHKT1;1屬于水稻高親和性K+轉(zhuǎn)運(yùn)蛋白(HKT)家族基因，對(duì)于水稻地上部鈉離子的排出至關(guān)重要，并受到一個(gè)MYB轉(zhuǎn)錄因子OsMYBc的調(diào)控。本研究首先獲得了該基因的突變體oshkt1;1，然后用自身啟動(dòng)子（Com）和一個(gè)不能被OsMYBc結(jié)合的突變啟動(dòng)子（mCom）驅(qū)動(dòng)OsHKT1;1基因轉(zhuǎn)化oshkt1;1oshkt1;1的耐鹽表型，這進(jìn)一步證實(shí)了該基因啟動(dòng)子對(duì)于它的表達(dá)的重要性。而且OsMYBc的過(guò)表達(dá)株系較之野生型水稻對(duì)鹽脅迫的耐受性顯著提高。酵母雙雜交實(shí)驗(yàn)顯示OsMYBc可以與一個(gè)E3連接酶——OsMSRFP發(fā)生互作，從而導(dǎo)致OsMYBc被26S蛋白酶體降解，導(dǎo)致OsHKT1;1的表達(dá)被抑制。OsMSRFP的敲除株系對(duì)鹽脅迫的耐受性也顯著提高。