Abstract
Helical growth is an economical way for plant to obtain resources. The classic microtubule–microfibril alignment model of Arabidopsis helical growth involves restriction of the appropriate orientation of cellulose microfibrils appropriately in the cell walls. However, the molecular mechanism underlying tomato helical growth remains unknown. Here, we identified a spontaneous tomato helical (hel) mutant with right-handed helical cotyledons and petals but left-handed helical stems and true leaves. Genetic analysis revealed that the hel phenotype was controlled by a single recessive gene. Using map-based cloning, we cloned the HEL gene, which encodes a cellulose interacting protein homologous to CSI1 of Arabidopsis. We identified a 27 bp fragment replacement that generated a premature stop codon. Transgenic experiments showed that the helical growth phenotype could be restored by the allele of this gene from wild-type Pyriforme. In contrast, the knockout mutation of HEL in Pyriforme via CRISPR/Cas9 resulted in helical growth. These findings shed light on the molecular control of the helical growth of tomato.
Highlights
The rational use of growing space is essential for plant photosynthesis and reproductive development and indirectly affects biotic and abiotic resistance
We identified the HEL gene, which encodes a cellulose synthase-interactive protein, via map-based cloning
We found that the cotyledons, petals and pistils of the hel mutant showed right-handed helical growth (Fig. 1a–f)
Summary
The rational use of growing space is essential for plant photosynthesis and reproductive development and indirectly affects biotic and abiotic resistance. Upright growth, and deep roots enable more solar radiation and CO2 to be absorbed, thereby minimizing intraplant competition, to achieve increased photosynthesis efficiency[1]. A growth axis is usually generated in plants due to the expansion of organs into space, and a vast majority of plants display linear or circumferential growth[2]. Due to the lack of strong xylem support, some plants evolve a helical growth axis to achieve increased heights by winding onto a support, as observed for climbing plants. Specific organs of climbing plants, such as tendrils in Vitis, Pisum sativum, and Cucurbitaceae, often exhibit helical growth[3]. Members of the legume family and other vine plants climb through stem circumnutation, the vast majority of which display a right-handed helix[4]. For some nonclimbing plants, pruning and bundling are essential for improving photosynthesis efficiency, and yield and quality in agriculture
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