State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources/Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (South China) of Ministry of Agriculture, College of Horticulture, South China Agricultural University, Guangzhou, China.
Guangdong Litchi Engineering Research Center, College of Horticulture, South China Agricultural University, Guangzhou, China.
Plant Cell Physiol. 2019 Feb 1;60(2):448-461. doi: 10.1093/pcp/pcy219.
During litchi (Litchi chinensis Sonn.) fruit ripening, two major physiological changes, degreening (Chl degradation) and pigmentation (anthocyanin biosynthesis), are visually apparent. However, the specific factor triggering this important transition is still unclear. In the present study, we found that endogenous ABA content increased sharply when Chl breakdown was initiated and the ABA level peaked just before the onset of anthocyanin accumulation, suggesting that ABA plays an important role during litchi fruit pigmentation. We characterized three ABSCISIC ACID RESPONSE ELEMENT-BINDING FACTORs (LcABF1/2/3) belonging to group A of the basic leucine zipper (bZIP) transcription factors previously shown to be involved in ABA signaling under abiotic stress. LcABF1 transcripts increased at the onset of Chl degradation, and the expression of LcABF3 accumulated in parallel with anthocyanin biosynthesis. In addition, dual luciferase and yeast one-hybrid assays indicated that LcABF1/2 recognized ABA-responsive elements in the promoter region of Chl degradation-related genes (PAO and SGR), while LcABF2/3 bound the promoter region of LcMYB1 and anthocyanin biosynthesis-related structural genes. Indeed, Nicotiana benthamiana leaves transiently expressing LcABF1/2 showed a senescence phenomenon with Chl degradation, and LcABF3 overexpression increased the accumulation of anthocyanin via activation of LcMYB1, which is the key determinant of anthocyanin biosynthesis. These data indicate that LcABF1/2/3 are important transcriptional regulators of ABA-dependent litchi fruit ripening involved in both Chl degradation and anthocyanin biosynthesis.
在荔枝（Litchi chinensis Sonn.）果实成熟过程中，有两个主要的生理变化，即褪绿（Chl 降解）和着色（花青素生物合成），这在视觉上是显而易见的。然而，触发这一重要转变的具体因素仍不清楚。在本研究中，我们发现，当 Chl 分解开始时，内源 ABA 含量急剧增加，而 ABA 水平在花青素积累开始前达到峰值，这表明 ABA 在荔枝果实着色过程中发挥着重要作用。我们鉴定了三个属于碱性亮氨酸拉链（bZIP）转录因子 A 组的 ABRE 结合因子（LcABF1/2/3），这些转录因子先前被证明在非生物胁迫下参与 ABA 信号转导。LcABF1 转录本在 Chl 降解开始时增加，而 LcABF3 的表达与花青素生物合成平行积累。此外，双荧光素酶和酵母单杂交实验表明，LcABF1/2 识别 Chl 降解相关基因（PAO 和 SGR）启动子区域中的 ABA 反应元件，而 LcABF2/3 结合 LcMYB1 和花青素生物合成相关结构基因启动子区域。事实上，在瞬时表达 LcABF1/2 的 Nicotiana benthamiana 叶片中，出现了 Chl 降解的衰老现象，而 LcABF3 的过表达通过激活 LcMYB1 增加了花青素的积累，LcMYB1 是花青素生物合成的关键决定因素。这些数据表明，LcABF1/2/3 是 ABA 依赖的荔枝果实成熟过程中 Chl 降解和花青素生物合成的重要转录调节因子。
