Gao Qiguo, Shi Songmei, Liu Yudong, Pu Quanming, Liu Xiaohuan, Zhang Ying, Zhu Liquan
Key Laboratory of Horticulture Science for Southern Mountainous Regions, Ministry of Education/College of Horticulture and Landscape Architecture, Southwest University, Chongqing, 400715, China.
College of Agronomy and Biotechnology, Southwest University, Chongqing, 400715, China.
Plant Reprod. 2016 Sep;29(3):239-50. doi: 10.1007/s00497-016-0287-5. Epub 2016 Jun 24.
M locus protein kinase, one of the SRK-interacting proteins, is a necessary positive regulator for the self-incompatibility response in Brassica. In B. rapa, MLPK is expressed as two different transcripts, MLPKf1 and MLPKf2, and either isoform can complement the mlpk/mlpk mutation. The AtAPK1B gene has been considered to be the ortholog of BrMLPK, and AtAPK1B has no role in self-incompatibility (SI) response in A. thaliana SRK-SCR plants. Until now, what causes the MLPK and APK1B function difference during SI response in Brassica and A. thaliana SRKb-SCRb plants has remained unknown. Here, in addition to the reported MLPKf1/2, we identified the new MLPKf1 homologous gene MLPKn1 from B. oleracea. BoMLPKn1 and BoMLPKf1 shared nucleotide sequence identity as high as 84.3 %, and the most striking difference consisted in two fragment insertions in BoMLPKn1. BoMLPKn1 and BoMLPKf1 had a similar gene structure; both their deduced amino acid sequences contained a typical plant myristoylation consensus sequence and a Ser/Thr protein kinase domain. BoMLPKn1 was widely expressed in petal, sepal, anther, stigma and leaf. Genome-wide survey revealed that the B. oleracea genome contained three MLPK homologous genes: BoMLPKf1/2, BoMLPKn1 and Bol008343n. The B. rapa genome also contained three MLPK homologous genes, BrMLPKf1/2, BraMLPKn1 and Bra040929. Phylogenetic analysis revealed that BoMLPKf1/2 and BrMLPKf1/2 were phylogenetically more distant from AtAPK1A than Bol008343n, Bra040929, BraMLPKn1 and BoMLPKn1, Synteny analysis revealed that the B. oleracea chromosomal region containing BoMLPKn1 displayed high synteny with the A. thaliana chromosomal region containing APK1B, whereas the B. rapa chromosomal region containing BraMLPKn1 showed high synteny with the A. thaliana chromosomal region containing APK1B. Together, these results revealed that BoMLPKn1/BraMLPKn1, and not the formerly reported BoMLPKf1/2 (BrMLPKf1/2), was the orthologous genes of AtAPK1B, and no ortholog of BoMLPKf1/2 (BrMLPKf1/2) was found in the A. thaliana genome. We speculated that Brassica MLPKf1/2 might have emerged after speciation of Brassica and A. thailiana, and that it was recruited to the SRK-triggered SI signaling cascade in Brassica.
M位点蛋白激酶是与SRK相互作用的蛋白之一，是芸苔属植物中自交不亲和反应所必需的正向调节因子。在白菜型油菜中，MLPK以两种不同的转录本MLPKf1和MLPKf2形式表达，任何一种同工型都可以弥补mlpk/mlpk突变。AtAPK1B基因被认为是BrMLPK的直系同源基因，而AtAPK1B在拟南芥SRK-SCR植物的自交不亲和（SI）反应中不起作用。到目前为止，在芸苔属植物和拟南芥SRKb-SCRb植物的SI反应过程中，导致MLPK和APK1B功能差异的原因仍不清楚。在此，除了已报道的MLPKf1/2外，我们从甘蓝中鉴定出了新的MLPKf1同源基因MLPKn1。BoMLPKn1和BoMLPKf1的核苷酸序列同一性高达84.3%，最显著的差异在于BoMLPKn1中有两个片段插入。BoMLPKn1和BoMLPKf1具有相似的基因结构；它们推导的氨基酸序列都包含一个典型的植物肉豆蔻酰化共有序列和一个Ser/Thr蛋白激酶结构域。BoMLPKn1在花瓣、萼片、花药、柱头和叶片中广泛表达。全基因组调查显示，甘蓝基因组包含三个MLPK同源基因：BoMLPKf1/2、BoMLPKn1和Bol008343n。白菜型油菜基因组也包含三个MLPK同源基因，即BrMLPKf1/2、BraMLPKn1和Bra040929。系统发育分析表明，与Bol008343n、Bra040929、BraMLPKn1和BoMLPKn1相比，BoMLPKf1/2和BrMLPKf1/2在系统发育上与AtAPK1A的距离更远。共线性分析表明，包含BoMLPKn1的甘蓝染色体区域与包含APK1B的拟南芥染色体区域具有高度共线性，而包含BraMLPKn1的白菜型油菜染色体区域与包含APK1B的拟南芥染色体区域也具有高度共线性。这些结果共同表明，BoMLPKn1/BraMLPKn1，而非先前报道的BoMLPKf1/2（BrMLPKf1/2），是AtAPK1B直系同源基因，并且在拟南芥基因组中未发现BoMLPKf1/2（BrMLPKf1/2）的直系同源基因。我们推测，芸苔属植物的MLPKf1/2可能在芸苔属植物和拟南芥物种形成后出现，并被招募到芸苔属植物中由SRK触发的SI信号级联反应中。
