Abstract
Drought stress is one of the major environmental factors that limited crop’s growth and production. Cassava known as a tropical crop that is widely distributed in Sub-Saharan Africa. It has a strong drought tolerance and can grow well under tough environmental conditions. Therefore, understanding how cassava responds to drought stress and coordinates survival and accumulation has great theoretical significance for improving crop drought resistance breeding. Many studies on cassava drought responses mainly focused on the leaf and whole seedling. Nevertheless, how the vasculature plays an important role in plant response to water deficiency remains to be fully elucidated. Here, comparative transcriptome analysis was performed on isolated mesophyll tissue and leaf vein vascular tissue of cassava variety KU50 after mild drought treatment to determine the molecular mechanism behind drought resistance in cassava vasculature. Our results showed that KU50 leaves had increased leaf temperature, with characters of rapidly decreased net photosynthetic rate, stomatal conductance, and transpiration rate in leaves, and the intercellular CO2 concentration accumulated under drought stress. Comparative transcriptome profiling revealed that under drought stress, leaf mesophyll tissue mainly stimulated the biosynthesis of amino acids, glutamic acid metabolism, and starch and sucrose metabolism. In particular, the arginine biosynthesis pathway was significantly enhanced to adapt to the water deficiency in leaf mesophyll tissue. However, in vascular tissue, the response to drought mainly involved ion transmembrane transport, hormone signal transduction, and depolymerization of proteasome. Concretely, ABA signaling and proteasome metabolism, which are involved in ubiquitin regulation, were changed under drought stress in KU50 leaf vascular tissue. Our work highlights that the leaf vasculature and mesophyll in cassava have completely different drought response mechanisms.
Highlights
Drought is a common abiotic stress that can curtail crop productivity (Tuberosa and Salvi 2006)
Forty-five days after cassava variety KU50 (Fig. 1A) was planted in a greenhouse, water was withdrawn for 3 days, and leaf temperature increased (Fig. 1C)
The leaf mid-vein stained with toluidine blue mainly consisted of vasculature tissue, including xylem, phloem, and ground tissue (Fig. 1B)
Summary
Drought is a common abiotic stress that can curtail crop productivity (Tuberosa and Salvi 2006). Seedlings, shoots, and roots had been used as materials to study water deficit stress. Carbon metabolism plays an important role in plant leaf abiotic resistance. Given the different drought responses of the shoots and roots, the drought resistance mechanism of plant vasculature has become a research hotspot. Insect stylet could provide relative pure phloem sap, it is not compatible with many studies due to its trivial amount of sap exudates from the stylet (Reidel et al 2009) These methods are associated with a critical issue in that only mobile molecules can be identified. Understanding how cassava responds to water deficiency in vasculature and mesophyll tissue of leaf is valuable for improving drought tolerance breeding of cassava and other crops. This work will expand our knowledge about how plants adapt to environmental stresses
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