Enns Linda C, Kanaoka Masahiro M, Torii Keiko U, Comai Luca, Okada Kiyotaka, Cleland Robert E
Department of Biology, University of Washington, Seattle, WA 98195, USA.
Plant Mol Biol. 2005 Jun;58(3):333-49. doi: 10.1007/s11103-005-4526-7.
Callose, a beta-1,3-glucan that is widespread in plants, is synthesized by callose synthase. Arabidopsis thaliana contains a family of 12 putative callose synthase genes (GSL1-12). The role of callose and of the individual genes in plant development is still largely uncertain. We have now used TILLING and T-DNA insertion mutants (gsl1-1, gsl5-2 and gsl5-3) to study the role of two closely related and linked genes, GSL1 and GSL5, in sporophytic development and in reproduction. Both genes are expressed in all parts of the plant. Sporophytic development was nearly normal in gsl1-1 homozygotes and only moderately defective in homozygotes for either of the two gsl5 alleles. On the other hand, plants that were gsl1-1/+ gsl5/gsl5 were severely defective, with smaller leaves, shorter roots and bolts and smaller flowers. Plants were fertile when the sporophytes had either two wild-type GSL1 alleles, or one GSL5 allele in a gsl1-1 background, but gsl1-1/+ gsl5/gsl5 plants produced an extremely reduced number of viable seeds. A chromosome with mutations in both GSL1 and GSL5 rendered pollen infertile, although such a chromosome could be transmitted via the egg. As a result, it was not possible to obtain plants that were homozygous for mutations in both the GSL genes. Pollen grain development was severely affected in double mutant plants. Many pollen grains were collapsed and inviable in the gsl1-1/gsl1-1 gsl5/+ and gsl1-1/+ gsl5/gsl5 plants. In addition, gsl1-1/+ gsl5/gsl5 plants produced abnormally large pollen with unusual pore structures, and had problems with tetrad dissociation. In this particular genotype, while the callose wall formed around the pollen mother cells, no callose wall separated the resulting tetrads. We conclude that GSL1 and GSL5 play important, but at least partially redundant roles in both sporophytic development and in the development of pollen. They are responsible for the formation of the callose wall that separates the microspores of the tetrad, and also play a gametophytic role later in pollen grain maturation. Other GSL genes may control callose formation at different steps during pollen development.
胼胝质是一种在植物中广泛存在的β-1,3-葡聚糖，由胼胝质合成酶合成。拟南芥含有一个由12个假定的胼胝质合成酶基因（GSL1 - 12）组成的家族。胼胝质以及各个基因在植物发育中的作用仍很大程度上不确定。我们现在利用定向诱导基因组局部突变（TILLING）和T-DNA插入突变体（gsl1-1、gsl5-2和gsl5-3）来研究两个密切相关且连锁的基因GSL1和GSL5在孢子体发育和繁殖中的作用。这两个基因在植物的所有部位均有表达。gsl1-1纯合子的孢子体发育近乎正常，而两个gsl5等位基因中任一个的纯合子仅有中度缺陷。另一方面，gsl1-1/+ gsl5/gsl5植株存在严重缺陷，叶片较小、根和花茎较短且花朵较小。当孢子体具有两个野生型GSL1等位基因，或在gsl1-1背景下有一个GSL5等位基因时，植株可育，但gsl1-1/+ gsl5/gsl5植株产生的 viable种子数量极少。一条同时具有GSL1和GSL5突变的染色体使花粉不育，尽管这样的染色体可通过卵细胞传递。因此，无法获得两个GSL基因均为纯合突变的植株。双突变植株的花粉粒发育受到严重影响。在gsl1-1/gsl1-1 gsl5/+和gsl1-1/+ gsl5/gsl5植株中，许多花粉粒皱缩且无活力。此外，gsl1-1/+ gsl5/gsl5植株产生异常大的花粉，具有不寻常的孔结构，并且在四分体解离方面存在问题。在这种特定基因型中，虽然在花粉母细胞周围形成了胼胝质壁，但没有胼胝质壁将产生的四分体分开。我们得出结论，GSL1和GSL5在孢子体发育和花粉发育中都发挥着重要但至少部分冗余的作用。它们负责形成分隔四分体小孢子的胼胝质壁，并且在花粉粒成熟后期也发挥配子体作用。其他GSL基因可能在花粉发育的不同阶段控制胼胝质的形成。
