On a global scale, drought, salinity, extreme temperature, and other abiotic stressors severely limit the quality and yield of crops. Therefore, it is crucial to clarify the adaptation strategies of plants to harsh environments. Chloroplasts are important environmental sensors in plant cells. For plants to thrive in different habitats, chloroplast homeostasis must be strictly regulated, which is necessary to maintain efficient plant photosynthesis and other metabolic reactions under stressful environments. To maintain normal chloroplast physiology, two important biological processes are needed: the import and degradation of chloroplast proteins. The orderly import of chloroplast proteins and the timely degradation of damaged chloroplast components play a key role in adapting plants to their environment. In this review, we briefly describe the mechanism of chloroplast TOC-TIC protein transport. The importance and recent progress of chloroplast protein turnover, retrograde signaling, and chloroplast protein degradation under stress are summarized. Furthermore, the potential of targeted regulation of chloroplast homeostasis is emphasized to improve plant adaptation to environmental stresses.

MYB转录因子在植物生长发育和抵御胁迫中起着重要的作用.为开展烟草(Nicotiana tabacum)NtMYB4a的功能研究和新种质的创制,本研究以NtMYB4a为靶基因,根据其CDS序列在第1和第3外显子上选定两个靶标Y1和B1,分别合成Oligo二聚体后和CRISPR载体连接,转化大肠杆菌(Escherichia coil)感受态DH5α后提取质粒并测序,将测序正确的质粒Y1-1和B1-1经LguⅠ酶切后用T4连接酶进行重组连接,成功构建了CRISPR/Cas9编辑系统的双靶标敲除载体,利用农杆菌(Agrobacterium tumefaciens)介导的叶盘法来转化烟草,经PCR和测序鉴定获得29株阳性植株,阳性率为24.37％,其中15株在靶点和非靶点处发生了不同程度的突变,共有4种突变类型,突变率为51.72％.初步观察发现NtMYB4a编辑T0代植株出现不同程度的矮化和花色变异,甚至死亡.qRT-PCR分析发现T0代植株花、茎、叶中NtMYB4a表达量不同程度下调.本研究为后续开展NtMYB4a的功能和以NtMYB4a为节点的分子调控机制研究提供了基础资料.

MYB转录因子是植物体内最大的一类转录因子,在植物应对非生物胁迫中发挥重要作用.为探讨烟草NtMYB4a基因在响应干旱、低温和茉莉酸甲酯胁迫下的功能,以NtMYB4a基因的过表达和敲除突变体及野生型烟株为材料,采用RT-qPCR技术分析了干旱、低温和茉莉酸甲酯处理0、1、3、6、12、24和48 h后烟草叶片中Nt-MYB4a的表达变化以及脯氨酸和丙二醛含量差异.结果显示:过表达突变体中NtMYB4a的表达量极显著高于野生型烟株,且不易受干旱、低温和茉莉酸甲酯胁迫的影响,烟叶中的脯氨酸含量增高,丙二醛含量降低;而基因敲除突变体中NtMYB4a的表达量显著低于野生型烟株,且易受干旱、低温和茉莉酸甲酯胁迫的影响,烟叶中的脯氨酸含量降低,丙二醛含量增加.此外,利用Plant CARE软件分析了NtMYB4a启动子区域,结果显示该区域含有赤霉素、生长素、脱落酸、茉莉酸甲酯、光、干旱、低温等激素和非生物胁迫相关的顺式作用元件.这些结果表明,Nt-MYB4a基因的表达受干旱、低温胁迫和茉莉酸甲酯的诱导,可能与烟株的抗逆性相关.

The MYB transcription factors are involved in the regulation of plant secondary metabolism, cell development and morphogenesis, and stress response. Here, a full-length, 816-bp NtMYB4a cDNA, which encodes a protein comprising 271 amino acids, was isolated from tobacco leaves. Phylogenetic analysis revealed that NtMYB4a is most similar to Nicotiana. attenuata MYB4, followed by Eriobotrya japonica MYB4, and NtMYB4a clustered with transcriptional activators rather than repressors. Subcellular localization assays showed that NtMYB4 localized in the nucleus, membrane, and cytoplasm. Expression analyses revealed differential expression of NtMYB4a among different tissues and organs and between different developmental stages, with most expression occurring in the stems and leaves during the full-bloom stage. Moreover, NtMYB4a expression was induced by cold, NaCl, PEG, abscisic acid, methyl jasmonate, and dark stressors, and the expression patterns and maximum expression levels varied with the type of stress. Overexpression of NtMYB4a upregulated NtPAL, Nt4CL, NtCHS, NtCHI, NtF3H, NtDFR, NtANS, and NtUFGT, which resulted in increased anthocyanin content in the tobacco corolla and darker colors. However, CRISPR/Cas9-mediated knockout of NtMYB4a downregulated NtPAL, NtC4H, Nt4CL, NtCHS, NtCHI, NtF3H, NtANS, and NtUFGT, which resulted in reduced anthocyanin content, and lighter corolla colors. These results indicated that NtMYB4a positively regulates anthocyanin biosynthesis and is involved in abiotic stress responses in tobacco plants.

MYB转录因子在植物的生长发育、生理代谢、细胞的形态和模式建成等生理过程中发挥重要作用.为了研究一个在优质烟草杂交种及其亲本中差异表达的R2R3-MYB转录因子NtMYB4a的功能.本研究采用PCR技术从烟草中分离出MYB4a的cDNA全长,构建NtMYB4a基因的过表达载体pART-CAM-NtMYB4a.通过根癌农杆菌介导法转化烟草自育品系GDH88获得转化植株,经卡那霉素抗性筛选得到162株抗性苗,PCR检测发现有67株阳性苗,转化率为41.4％.qRT-PCR检测表明NtMYB4a基因在转基因植株的花、茎和叶中的表达量显著提高.为后续研究NtMYB4a的功能提供了试验材料与研究基础.