Anatomical and hormonal description of rootlet primordium development along white lupin cluster root

Abstract

Cluster root (CR) is one of the most spectacular plant developmental adaptations to hostile environment. It can be found in a few species from a dozen botanical families, including white lupin (Lupinus albus) in the Fabaceae family. These amazing structures are produced in phosphate‐deprived conditions and are made of hundreds of short roots also known as rootlets. White lupin is the only crop bearing CRs and is considered as the model species for CR studies. However, little information is available on CRs atypical development, including the molecular events that trigger their formation. To provide insights on CR formation, we performed an anatomical and cellular description of rootlet development in white lupin. Starting with a classic histological approach, we described rootlet primordium development and defined eight developmental stages from rootlet initiation to their emergence. Due to the major role of hormones in the developmental program of root system, we next focussed on auxin‐related mechanisms. We observed the establishment of an auxin maximum through rootlet development in transgenic roots expressing the DR5:GUS auxin reporter. Expression analysis of the main auxin‐related genes [TIR, Auxin Response Factor (ARF) and AUX/IAA] during a detailed time course revealed specific expression associated with the formation of the rootlet primordium. We showed that L. albus TRANSPORT INHIBITOR RESPONSE 1b is expressed during rootlet primordium formation and that L. albus AUXIN RESPONSE FACTOR 5 is expressed in the vasculature but absent in the primordium itself. Altogether, our results describe the very early cellular events leading to CR formation and reveal some of the auxin‐related mechanisms.

Leaf Phosphorus Concentration Regulates the Development of Cluster Roots and Exudation of Carboxylates in Macadamia integrifolia

“…The formation of cluster roots and carboxylate exudation induced by low P availability have been studied extensively in L. albus (Shane et al, 2003b;Wasaki et al, 2003;Shen et al, 2005;Li et al, 2008;Cheng et al, 2014;Gallardo et al, 2019), and many species of Proteaceae like Hakea sp. (Lamont, 1972a,b), Grevillea robusta (Skene et al, 1996(Skene et al, , 1998, H. prostrata (Shane et al, 2003a), Grevillea crithmifolia (Shane and Lambers, 2006), and Euplassa cantareirae (de Britto Costa et al, 2016).…”

A High-Throughput Phenotyping Tool to Identify Field-Relevant Anthracnose Resistance in White Lupin

“…(lupini) makes lupins highly efficient atmospheric nitrogen fixers (Fernández-Pascual et al 2007;Peix et al 2015). Additionally, white lupin is capable of forming specialized cluster roots which release carboxylates to mobilize poorly available phosphorus sources (Gallardo et al 2019;Lambers et al 2013). White lupin is recognized for its high protein content (36 to 38%), starch-free white seeds, outstanding fatty acid quality and additional health benefits, making its grains ideal for the food and feed industry (Arnoldi et al 2015;Boschin et al 2008;Monteiro et al 2014).…”

Stress tolerance in flax plants inoculated with Bacillus and Azotobacter species under deficit irrigation

“…PGPRs reportedly enhance RWC and dry matter through increasing choline production as a precursor to glycine betaine (as a means of osmotic regulation) (Vurukonda et al 2016). Alternatively, bacterially-produced indole acetic acid (Table 1) might improve leaf water content through enhanced root growth (Gallardo et al 2018) and soil water absorption. Barnawal et al (2017) reported that, compared to non-inoculated plants, PGPRs inoculated ones exhibited enhanced stomatal conductance under stressful conditions, possibly indicating the effects of these bacteria on maintaining plant water content due to optimal stomata conductance.…”