Complex cell shapes are generated first by breaking symmetry, and subsequent polar growth. Localized bending of anticlinal walls initiates lobe formation in the epidermal pavement cells of cotyledons and leaves, but how the microtubule cytoskeleton mediates local cell growth, and how plant pavement cells benefit from adopting jigsaw puzzle-like shapes, are poorly understood. In Arabidopsis (Arabidopsis thaliana), the basic Pro-rich protein (BPP) microtubule-associated protein family comprises seven members. We analyzed lobe morphogenesis in cotyledon pavement cells of a BPP1;BPP2;BPP5 triple knockout mutant. New image analysis methods (MtCurv and BQuant) showed that anticlinal microtubule bundles were significantly reduced and cortical microtubules that fan out radially across the periclinal wall did not enrich at the convex side of developing lobes. Despite these microtubule defects, new lobes were initiated at the same frequency as in wild-type cells, but they did not expand into well-defined protrusions. Eventually, mutant cells formed nearly polygonal shapes and adopted concentric microtubule patterns. The mutant periclinal cell wall bulged outward. The radius of the calculated inscribed circle of the pavement cells, a proposed proxy for maximal stress in the cell wall, was consistently larger in the mutant cells during cotyledon development, and correlated with an increase in cell height. These bpp mutant phenotypes provide genetic and cell biological evidence that initiation and growth of lobes are distinct morphogenetic processes, and that interdigitated cell geometry effectively suppresses large outward bulging of pavement cells.

中文翻译：

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富含脯氨酸的基本蛋白质介导的微管对于叶生长和扁平细胞几何形状至关重要。

复杂的细胞形状首先通过打破对称性以及随后的极性生长而产生。垂周壁的局部弯曲引发了子叶和叶子的表皮铺装细胞中的叶形成，但是微管细胞骨架如何介导局部细胞生长，以及植物铺装细胞如何从采用拼图形状中受益，人们知之甚少。在拟南芥（Arabidopsis thaliana）中，碱性富含Pro蛋白（BPP）微管相关蛋白家族由七个成员组成。我们分析了 BPP1;BPP2;BPP5 三重敲除突变体的子叶铺装细胞中的叶形态发生。新的图像分析方法（MtCurv 和 BQuant）表明，背斜微管束显着减少，并且沿周壁呈放射状散开的皮质微管在发育中的叶的凸侧并未富集。尽管存在这些微管缺陷，新的叶以与野生型细胞相同的频率启动，但它们没有扩展成明确的突起。最终，突变细胞形成接近多边形的形状并采用同心微管模式。突变体的周周细胞壁向外凸出。计算出的路面细胞内切圆的半径（细胞壁最大应力的代表）在子叶发育过程中突变细胞中始终较大，并且与细胞高度的增加相关。这些 bpp 突变表型提供了遗传和细胞生物学证据，表明叶的起始和生长是不同的形态发生过程，并且叉指状的细胞几何形状有效地抑制了路面细胞的大量向外凸出。