Zhao Chengsong, Craig Johanna C, Petzold H Earl, Dickerman Allan W, Beers Eric P
Department of Horticulture , Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
Plant Physiol. 2005 Jun;138(2):803-18. doi: 10.1104/pp.105.060202. Epub 2005 May 27.
The growth of secondary xylem and phloem depends on the division of cells in the vascular cambium and results in an increase in the diameter of the root and stem. Very little is known about the genetic mechanisms that control cambial activity and the differentiation of secondary xylem and phloem cell types. To begin to identify new genes required for vascular cell differentiation and function, we performed genome-wide expression profiling of xylem and phloem-cambium isolated from the root-hypocotyl of Arabidopsis (Arabidopsis thaliana). Gene expression in the remaining nonvascular tissue was also profiled. From these transcript profiles, we assembled three sets of genes with expression significantly biased toward xylem, phloem-cambium, or nonvascular tissue. We also assembled three two-tissue sets of genes with expression significantly biased toward xylem/phloem-cambium, xylem/nonvascular, or phloem-cambium/nonvascular tissues. Localizations predicted by transcript profiles were supported by results from promoter-reporter and reverse transcription-polymerase chain reaction experiments with nine xylem- or phloem-cambium-biased genes. An analysis of the members of the phloem-cambium gene set suggested that some genes involved in regulating primary meristems are also regulators of the cambium. Secondary phloem was implicated in the synthesis of auxin, glucosinolates, cytokinin, and gibberellic acid. Transcript profiles also supported the importance of class III HD ZIP and KANADI transcription factors as regulators of radial patterning during secondary growth, and identified several members of the G2-like, NAC, AP2, MADS, and MYB transcription factor families that may play roles as regulators of xylem or phloem cell differentiation and activity.
次生木质部和韧皮部的生长取决于维管形成层中细胞的分裂，并导致根和茎直径的增加。关于控制形成层活性以及次生木质部和韧皮部细胞类型分化的遗传机制，我们所知甚少。为了开始鉴定维管细胞分化和功能所需的新基因，我们对从拟南芥根下胚轴分离出的木质部和韧皮部-形成层进行了全基因组表达谱分析。还对其余非维管组织中的基因表达进行了分析。从这些转录谱中，我们组装了三组基因，其表达明显偏向木质部、韧皮部-形成层或非维管组织。我们还组装了三组双组织基因集，其表达明显偏向木质部/韧皮部-形成层、木质部/非维管组织或韧皮部-形成层/非维管组织。转录谱预测的定位得到了九个木质部或韧皮部-形成层偏向基因的启动子-报告基因和逆转录-聚合酶链反应实验结果的支持。对韧皮部-形成层基因集成员的分析表明，一些参与调控初生分生组织的基因也是形成层的调控因子。次生韧皮部与生长素、芥子油苷、细胞分裂素和赤霉素的合成有关。转录谱还支持III类HD ZIP和KANADI转录因子作为次生生长过程中径向模式调控因子的重要性，并鉴定了G2样、NAC、AP2、MADS和MYB转录因子家族的几个成员，它们可能作为木质部或韧皮部细胞分化和活性的调控因子发挥作用。
