荔枝分枝调控基因LcSMXL7的鉴定及功能分析

Identification and Functional Analysis of Litchi Branching Regulator LcSMXL7

荔枝是华南地区最具特色的水果之一,目前我国荔枝栽培面积约53万hm^(2),产量230万t。荔枝花序呈聚伞花序圆锥状排列,分枝数量过多会消耗树体大量营养,影响荔枝坐果。SUPPRESSOR OF MAX21-LIKE 7(SMXL7)是独脚金内酯信号途径的重要组分,是具有抑制子和转录因子双重功能的新型抑制子,参与调控植物的分枝发育。为了鉴定荔枝花穗分枝发育的调控基因,本研究以‘妃子笑/怀枝’砧穗组合荔枝结果树花穗为试材,利用RNA-seq数据克隆荔枝SMXL7基因家族成员LcSMXL7,并对其基因序列、理化性质、保守结构域、进化关系、组织表达特异性,基因功能及亚细胞定位进行分析。分析结果显示,该基因ORF全长3408 bp,编码1135个氨基酸;编码蛋白含有2个Clp结构域和1个AAA_2结构域;在茎、种子和叶片中表达较高,在花穗、雄花和果皮中表达次之,而在雌花、果肉和根中的表达最低;LcSMXL7的分子式为C_(5429)H_(8632)N_(1530)O_(1715)S_(38),理论相对分子质量(Mw)为123.99 kDa,理论等电点(pI)约为5.96,蛋白脂溶指数为83.74,蛋白不稳定指数为46.38,亲水性平均系数为-0.305,与来自木本果树甜橙和杧果的SMXL7蛋白的关系较近,亚细胞定位在细胞核;在拟南芥中过表达LcSMXL7可显著提高拟南芥的分枝数量。推测LcSMXL7可作为转录因子参与基因表达调控,该研究为进一步探索LcSMXL7调控荔枝花穗发育的分子机制奠定了基础。

Litchi(Litchi chinensis Sonn.)is one of the most distinctive fruits in South China and is one of the pillar in-dustries of rural economy in South China.At present,the cultivated area of litchi in China is more than 533000 hm^(2)and the output is more than 2.3 million tons,accounting for more than 80%of the total cultivated area and more than 65%of the total output in the world.The panicle of litchi is paniculate,terminal,generally composed of cymes,with a length of 10‒40 cm and 200‒1500 florets.Excessive number of florets will consume tree nutrition and affect litchi fruit setting.Therefore,reducing the number of florets by regulating branches is an effective measure to improve fruit setting.SUP-PRESSOR OF MAX21-LIKE 7(SMXL7)is an important component of strigolactone signaling pathway and a new inhibitor with dual functions.SMXL7 is involved in leaf morphology regulating and branch development in Arabidopsis and rice.In order to identify the regulatory factors involved in the panicle branch development in litchi,LcSMXL7 the homologous of arabidopsis SMXL7 was cloned,the sequence of LcSMXL7 was obtained from RNA-seq data and the gene sequence,physicochemical properties,evolutionary relationships,conserved domain,tissue expression pattern,subcellular localization and gene function were analyzed.The open reading frame of LcSMXL7 was 3408 bp length,encoding 1135 amino acids.LcSMXL7 protein contained two CLP domains and one AAA_2 domain.The molecular formula,molecular weight and theoretical isoelectric point of LcSMXL7 was C_(5429)H_(8632)N_(1530)O_(1715)S_(38),123.99 kDa and 5.96.The Instability index,aliphatic index and grand average of hydropathicity of LcSMXL7 was 46.38,83.74 and‒0.305,respectively.LcSMXL7 was highly expressed in stems,seeds and leaves,followed by panicle,male flowers and pericarps,while the expression was low in female flowers,pulp and roots.Phylogenetic tree analysis showed that LcSMXL7 was closely related to SMXL7 protein from woody fruit trees sweet orange and mango.Subcellular localiza-tion analysis showed that LcSMXL7 was located in the nucleus,suggesting that it may participate in the regulation of gene expression as a transcription factor.Transgenic results showed that overexpression of LcSMXL7 in Arabidopsis could significantly increase the number of branches,indicating that LcSMXL7 could positively regulate the development of branches in Arabidopsis.We clarified the LcSMXL7 protein characteristics,tissue expression pattern,evolutionary relationships,conserved domain,subcellular localization and gene function,which would build a foundation for eluci-dating the molecular mechanism of LcSMXL7 in branch development.