Nolan Kim E, Irwanto Rina R, Rose Ray J
University of Newcastle and Australian Research Council Centre of Excellence for Integrative Legume Research, School of Environmental and Life Sciences University, Dr. Callaghan, NSW 2308, Australia.
Plant Physiol. 2003 Sep;133(1):218-30. doi: 10.1104/pp.103.020917.
We have cloned a SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) gene from Medicago truncatula (MtSERK1) and examined its expression in culture using real time PCR. In the presence of the auxin 1-naphthaleneacetic acid (NAA) alone, root differentiation occurs from the proliferating calli in both the cultured highly embryogenic seed line (2HA) and a low to nonembryogenic seed line (M. truncatula cv Jemalong). Auxin stimulated MtSERK1 expression in both 2HA and M. truncatula cv Jemalong. Embryo induction in proliferating calli requires a cytokinin in M. truncatula and unlike root formation is substantively induced in 2HA, not M. truncatula cv Jemalong. On embryo induction medium containing NAA and the cytokinin 6-benzylaminopurine (BAP), expression of MtSERK1 is elevated within 2 d of initiation of culture in both M. truncatula cv Jemalong and 2HA. However, MtSERK1 expression is much higher when both NAA and BAP are in the medium. BAP potentiates the NAA induction because MtSERK1 expression is not up-regulated by BAP alone. The 2HA genotype is able to increase its embryo formation because of the way it responds to cytokinin, but not because of the cytokinin effect on MtSERK1. Although the studies with M. truncatula indicate that somatic embryogenesis is associated with high SERK expression, auxin alone does not induce somatic embryogenesis as in carrot (Daucus carota) and Arabidopsis. Auxin in M. truncatula induces roots, and there is a clear up-regulation of MtSERK1. Although our analyses suggest that MtSERK1 is orthologous to AtSERK1, which in Arabidopsis is involved in somatic embryogenesis, in legumes, MtSERK1 may have a broader role in morphogenesis in cultured tissue rather than being specific to somatic embryogenesis.
我们从蒺藜苜蓿中克隆了一个体细胞胚胎发生受体激酶（SERK）基因（MtSERK1），并使用实时PCR检测了其在培养物中的表达。仅在生长素1-萘乙酸（NAA）存在的情况下，培养的高胚性种子系（2HA）和低胚性至非胚性种子系（蒺藜苜蓿品种Jemalong）的增殖愈伤组织均会发生根分化。生长素刺激了2HA和蒺藜苜蓿品种Jemalong中MtSERK1的表达。蒺藜苜蓿中增殖愈伤组织的胚胎诱导需要细胞分裂素，与根的形成不同，2HA中能实质性地诱导胚胎形成，而蒺藜苜蓿品种Jemalong中则不能。在含有NAA和细胞分裂素6-苄基腺嘌呤（BAP）的胚胎诱导培养基上，蒺藜苜蓿品种Jemalong和2HA在培养开始后的2天内MtSERK1的表达均升高。然而，当培养基中同时存在NAA和BAP时，MtSERK1的表达要高得多。BAP增强了NAA的诱导作用，因为单独的BAP不会上调MtSERK1的表达。2HA基因型能够增加其胚胎形成，是因为它对细胞分裂素的响应方式，而不是因为细胞分裂素对MtSERK1的影响。尽管对蒺藜苜蓿的研究表明体细胞胚胎发生与高SERK表达相关，但单独的生长素不会像在胡萝卜（胡萝卜属）和拟南芥中那样诱导体细胞胚胎发生。蒺藜苜蓿中的生长素诱导根的形成，并且MtSERK1有明显的上调。尽管我们的分析表明MtSERK1与AtSERK1是直系同源基因，AtSERK1在拟南芥中参与体细胞胚胎发生，但在豆科植物中，MtSERK1在培养组织的形态发生中可能具有更广泛的作用，而不是特异性地参与体细胞胚胎发生。
