Sizani Bulelani L, Krinsky Keelan, Mokoka Oboikanyo A, Rey Marie E C
School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg, South Africa.
PLoS One. 2025 Jun 4;20(6):e0318442. doi: 10.1371/journal.pone.0318442. eCollection 2025.
South African cassava mosaic virus (SACMV) is one of several bipartite begomoviruses that cause cassava mosaic disease (CMD) which reduces the production yield of the cassava (Manihot esculenta Crantz) crop in many tropical and subtropical regions. SACMV DNA-A and DNA-B encoded-proteins act as virulence factors that aid in inducing different disease severity depending on the host response. Recent evidence suggests a mutual potentiation of cell membrane receptor-associated pattern-triggered immunity (PTI) and nucleotide leucine-rich repeat (NLR) effector-associated immunity (ETI) in plant immune responses. This study aimed to compare expression of SACMV virulence factors, and PTI/ETI, in SACMV-infected susceptible T200 and tolerant TME3 cultivars. Expression of SACMV virulence factors differed between SACMV-infected T200 and TME3 plants at 12, 32 and 67 days post infection (dpi). Notably, at the early stage of infection (12 dpi), expression in TME3 of AV1 and AC2 virulence factors were 10-fold and 30-fold down-regulated, respectively, compared to susceptible T200. At systemic infection (32 dpi) AV1 expression was also significantly lower (4-fold) in TME3 compared to T200. Expression of AC2 (that targets host innate immunity), while significantly lower in both T200 and TME3 at 32 dpi compared to 12 dpi, was also significantly down-regulated (16-fold) in TME3 compared to T200. TME3 recovers around 67 dpi and virus load decreases by 33%, while in T200, symptoms and high SACMV replication persist. Identification and comparison of induced PTI and ETI associated genes upon SACMV-infection in susceptible T200 and tolerant/recovery TME3 cassava genotypes was achieved by whole transcriptome sequencing (RNA-seq) and by reverse transcriptase quantitative PCR (RT-qPCR). Analyses revealed reduced expression of PTI-associated signalling and response genes during SACMV systemic/symptomatic infection (32 dpi) in cassava genotypes. In addition, hydrogen peroxide (H2O2) production, a PTI indicator, was significantly reduced in the symptomatic viral infection stage at 32 dpi. Concurrently at 32 dpi, transcription of ETI signalling and response genes as well as SA biosynthesis and response genes, were upregulated during SACMV systemic infection in TME3. These results indicate that SACMV targets PTI-associated genes during systemic infection at 32 dpi to subvert PTI-mediated antiviral immunity in cassava, which results in reduced induction of ROS production. Differential expression of specific NLR-associated genes also differed between susceptible and tolerant cultivars at 12, 32 and 67 dpi. SACMV virulence factors were shown to play a role in symptom severity in T200 and TME3.
南非木薯花叶病毒（SACMV）是几种双分体菜豆金色花叶病毒之一，可引发木薯花叶病（CMD），这种病害会降低许多热带和亚热带地区木薯（Manihot esculenta Crantz）作物的产量。SACMV的DNA - A和DNA - B编码蛋白作为毒力因子，根据宿主反应诱导不同的病害严重程度。最近的证据表明，在植物免疫反应中，细胞膜受体相关的模式触发免疫（PTI）和核苷酸富含亮氨酸重复序列（NLR）效应子相关免疫（ETI）存在相互增强作用。本研究旨在比较SACMV感染的易感品种T200和耐病品种TME3中SACMV毒力因子以及PTI/ETI的表达情况。在感染后12天、32天和67天，SACMV感染的T200和TME3植株中SACMV毒力因子的表达存在差异。值得注意的是，在感染早期（12 dpi），与易感的T200相比，TME3中AV1和AC2毒力因子的表达分别下调了10倍和30倍。在系统感染阶段（32 dpi），TME3中AV1的表达也显著低于T200（4倍）。AC2（靶向宿主固有免疫）的表达，虽然在32 dpi时与12 dpi相比在T200和TME3中均显著降低，但与T200相比，TME3中也显著下调（16倍）。TME3在大约67 dpi时恢复，病毒载量降低33%，而在T200中，症状和高SACMV复制持续存在。通过全转录组测序（RNA - seq）和逆转录定量PCR（RT - qPCR），对易感的T200和耐病/恢复的TME3木薯基因型在SACMV感染后诱导的PTI和ETI相关基因进行了鉴定和比较。分析表明，在木薯基因型的SACMV系统/症状性感染（32 dpi）期间，PTI相关信号传导和反应基因的表达降低。此外，作为PTI指标的过氧化氢（H2O2）产量在32 dpi的症状性病毒感染阶段显著降低。同时在32 dpi时，TME3在SACMV系统感染期间，ETI信号传导和反应基因以及SA生物合成和反应基因的转录上调。这些结果表明，SACMV在32 dpi的系统感染期间靶向PTI相关基因，以破坏木薯中PTI介导的抗病毒免疫，从而导致ROS产生的诱导减少。在12天、32天和67 dpi时，易感品种和耐病品种中特定NLR相关基因的差异表达也有所不同。SACMV毒力因子在T200和TME3的症状严重程度中发挥作用。
