Involvement of HD-ZIP I transcription factors LcHB2 and LcHB3 in fruitlet abscission by promoting transcription of genes related to the biosynthesis of ethylene and ABA in litchi
Involvement of HD-ZIP I transcription factors LcHB2 and LcHB3 in fruitlet abscission by promoting transcription of genes related to the biosynthesis of ethylene and ABA in litchi
复制标题
HD-ZIP I转录因子LcHB2和LcHB3通过促进荔枝乙烯和ABA生物合成相关基因的转录参与果实脱落
DOI：
10.1093/treephys/tpz071
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发表时间：
2019-09-01
期刊：
影响因子：
4
通讯作者：
Li, Jianguo
中科院分区：
文献类型：
--
作者：
Ma, Xingshuai;Li, Caiqin;Li, Jianguo
荔枝是南亚重要的经济水果，其幼果脱落异常是荔枝生产的一个限制因素。乙烯和脱落酸（阿坝）都能诱导植物器官的脱落。虽然ACS/ACO和NCED基因分别编码乙烯和阿坝生物合成所需的关键酶，但这些基因在植物器官脱落过程中的转录调控尚不清楚。在此，我们鉴定了两个多聚半乳糖醛酸酶（PG）基因（LcPG 1和LcPG 2）和两个新的同源域亮氨酸拉链I转录因子基因（LcHB 2和LcHB 3），它们是与荔枝幼果萌发相关的关键基因。LcPG 1和LcPG 2的表达与荔枝幼果的成熟密切相关，与幼果成熟区PG活性增强和同型半乳糖醛酸含量降低一致。乙烯利和阿坝能增强LcPG 1/2的启动子活性。此外，幼果中乙烯和阿坝的产生也显著增加。结果表明，FAZ中与乙烯生物合成相关的5个基因（LcACO 2、LcACO 3、LcACS 1、LcACS 4和LcACS 7）和与ABA生物合成相关的1个基因（LcNCED 3）的表达被激活。电泳迁移率变动分析和瞬时表达实验表明，LcHB 2和LcHB 3均能直接与LcACO 2/3、LcACS 1/4/7和LcNCED 3基因的启动子结合并激活其表达。综上所述，我们推测LcHB 2/3可能通过对乙烯和阿坝的生物合成进行正调控而参与荔枝幼果的萌发。
Abnormal fruitlet abscission is a limiting factor in the production of litchi, an economically important fruit in Southern Asia. Both ethylene and abscisic acid (ABA) induce organ abscission in plants. Although ACS/ACO and NCED genes are known to encode key enzymes required for ethylene and ABA biosynthesis, respectively, the transcriptional regulation of these genes is unclear in the process of plant organ shedding. Here, two polygalacturonase (PG) genes (LcPG1 and LcPG2) and two novel homeodomain-leucine zipper I transcription factors genes (LcHB2 and LcHB3) were identified as key genes associated with the fruitlet abscission in litchi. The expression of LcPG1 and LcPG2 was strongly associated with litchi fruitlet abscission, consistent with enhanced PG activity and reduced homogalacturonan content in fruitlet abscission zones (FAZs). The promoter activities of LcPG1/2 were enhanced by ethephon and ABA. In addition, the production of ethylene and ABA in fruitlets was significantly increased during fruit abscission. Consistently, expression of five genes (LcACO2, LcACO3, LcACS1, LcACS4 and LcACS7) related to ethylene biosynthesis and one gene (LcNCED3) related to ABA biosynthesis in FAZs were activated. Further, electrophoretic mobility shift assays and transient expression experiments demonstrated that both LcHB2 and LcHB3 could directly bind to the promoter of LcACO2/3, LcACS1/4/7 and LcNCED3 genes and activate their expression. Collectively, we propose that LcHB2/3 are involved in the litchi fruitlet abscission through positive regulation of ethylene and ABA biosynthesis.