Douglas Scott J, Riggs C Daniel
Botany Department, University of Toronto, 1265 Military Trail, Scarborough, Ontario, Canada M1C1A4.
Dev Biol. 2005 Aug 15;284(2):451-63. doi: 10.1016/j.ydbio.2005.06.011.
Although the regulation of Arabidopsis floral meristem patterning and determinacy has been studied in detail, very little is known about the genetic mechanisms directing development of the pedicel, the short stem linking the flower to the inflorescence axis. Here, we provide evidence that the pedicel consists of a proximal portion derived from the young flower primordium, and a bulged distal region that emerges from tissue at the bases of sepals in the floral bud. Distal pedicel growth is controlled by the KNOTTED1-like homeobox gene BREVIPEDICELLUS (BP), as 35S::BP plants show excessive proliferation of pedicel tissue, while loss of BP conditions a radial constriction around the distal pedicel circumference. Mutant radial constrictions project proximally along abaxial and lateral sides of pedicels, leading to occasional downward bending at the distal pedicel. This effect is severely enhanced in a loss-of-function erecta (er) background, resulting in radially constricted tissue along the entire abaxial side of pedicels and downward-oriented flowers and fruit. Analysis of pedicel vascular patterns revealed biasing of vasculature towards the abaxial side, consistent with a role for BP and ER in regulating a vascular-borne growth inhibitory signal. BP expression in a reporter line marked boundaries between the inflorescence stem and lateral organs and the receptacle and floral organs. This boundary expression appears to be important to prevent homeotic displacement of node and lateral organ fates into underlying stem tissue. To investigate interactions between pedicel and flower development, we crossed bp er into various floral mutant backgrounds. Formation of laterally-oriented bends in bp lfy er pedicels paralleled phyllotaxy changes, consistent with a model where the architecture of mutant stems is controlled by both organ positioning and vasculature patterns. Collectively, our results indicate that the BP gene acts in Arabidopsis stems to confer a growth-competent state that counteracts lateral-organ associated asymmetries and effectively radializes internode and pedicel growth and differentiation patterns.
尽管拟南芥花分生组织模式形成和确定性的调控已得到详细研究，但对于指导花梗（连接花与花序轴的短茎）发育的遗传机制却知之甚少。在此，我们提供证据表明，花梗由源自幼花原基的近端部分和从花芽中萼片基部组织长出的膨大部分组成。花梗远端的生长受类KNOTTED1同源异型盒基因BREVIPEDICELLUS（BP）的控制，因为35S::BP植株表现出花梗组织过度增殖，而BP缺失则导致花梗远端周长出现径向收缩。突变体的径向收缩沿花梗的远轴侧和侧面近端延伸，导致花梗远端偶尔向下弯曲。在功能缺失的erecta（er）背景下，这种效应会严重增强，导致花梗整个远轴侧的组织径向收缩以及花和果实向下生长。对花梗维管模式的分析表明维管系统偏向远轴侧，这与BP和ER在调节维管介导的生长抑制信号中的作用一致。报告基因系中BP的表达标记了花序茎与侧器官以及花托与花器官之间的边界。这种边界表达对于防止节和侧器官命运异位到下方的茎组织中似乎很重要。为了研究花梗与花发育之间的相互作用，我们将bp er与各种花突变体背景进行杂交。bp lfy er花梗中侧向弯曲的形成与叶序变化平行，这与一个模型相符，即突变体茎的结构由器官定位和维管模式共同控制。总体而言，我们的结果表明，BP基因在拟南芥茎中发挥作用，赋予一种生长能力状态，以抵消与侧器官相关的不对称性，并有效地使节间和花梗的生长及分化模式呈辐射状。
