Heading in vegetable crops

admin

(Contributed by  Li Bo)

        Heading is an important horticultural trait in vegetables, which improves leaf texture, facilitates harvesting, and increases shelf life. There are several vegetables have leafy heads, such as Chinese cabbage (Brassica rapa ssp. pekinensis), endive (Chicorium endivia), cabbage (Brassica oleracea var. capitata), and mustard (Brassica juncea). Analysis of recombinant inbred lines from cabbage yielded 18 quantitative trait loci (QTLs) associated with heading[1]. microRNAs may also regulate the heading phenotype. The overexpression of miR319a down-regulated its target gene (BrpTCP4-1) and led to the altered development of the leafy head in Chinese cabbage[2]. A comparison of the B. rapa and B. oleracea genomes provides evidence that genes controlling dorsoventrality were subjected to strong selection bias in the heading cultivars of these two vegetable crops[3].

        Heading in vegetable crops is considered to be a developental disorder of leaf dorsoventrality. Genes involved in leaf dorsoventrality include AS1, AS2, miR390, TAS3, KAN, ARF3, ARF4, PHB, and REV[4-10], which are directly or indirectly regulated by key developmental regulators of leaves, such as members of the KNOXI (knotted-1 like homeobox gene) family[11,12]. In Arabidopsis, there have four genes belongs the KNOXI.
In the last few decades, little is known about the genetic and molecular mechanisms responsible for heading in Lettuce. Yu et al.[13] cloned a major qtl controlling heading in lettuce and confirmed the role of LsKN1 in heading. In heading lettuce, there is a CACTA-like transposon inserted, drive high expression of LsKN1▽. Finally confirmed that the LsKN1▽ protein binds the promoter of LsAS1 and down-regulates its expression to alter leaf dorsoventrality.
  
Reference:
[1] Yu X, Wang H, Zhong W, Bai J, Liu P, He Y. QTL mapping of leafy heads by genome resequencing in the RIL population of Brassica rapa. PLoS One 8, e76059 (2013).
[2] Mao Y, Wu F, Yu X, Bai J, Zhong W, He Y. MicroRNA319a-targeted Brassica rapa ssp. pekinensis TCP genes modulate head shape in Chinese cabbage by differential cell division arrest in leaf regions. Plant Physiol. 164, 710–720 (2014).
[3] Cheng F, Sun R, Hou X, Zheng H, Zhang F, Zhang Y, Liu B, Liang J, Zhuang M, Liu Y, Liu D, Wang X, Li P, Liu Y, Lin K, Bucher J, Zhang N, Wang Y, Wang H, Deng J, Liao Y, Wei K, Zhang X, Fu L, Hu Y, Liu J, Cai C, Zhang S, Zhang S, Li F, Zhang H, Zhang J, Guo N, Liu Z, Liu J, Sun C, Ma Y, Zhang H, Cui Y, Freeling MR, Borm T, Bonnema G, Wu J, Wang X. Subgenome parallel selection is associated with morphotype diversification and convergent crop domestication in Brassica rapa and Brassica oleracea. Nat. Genet. 48, 1218–1224 (2016).
[4] Byrne ME, Barley R, Curtis M, Arroyo JM, Dunham M, Hudson A, Martienssen RA. Asymmetric leaves1 mediates leaf patterning and stem cell function in Arabidopsis. Nature 408, 967–971 (2000).
[5] Byrne ME. Networks in leaf development. Curr. Opin. Plant Biol. 8, 59–66 (2005).
[6] Juarez MT, Kui JS, Thomas J, Heller BA, Timmermans MC. microRNAmediated repression of rolled leaf1 specifies maize leaf polarity. Nature 428, 84–88 (2004).
[7] Matsumura Y, Iwakawa H, Machida Y, Machida C. Characterization of genes in the ASYMMETRIC LEAVES2/LATERAL ORGAN BOUNDARIES (AS2/LOB) family in Arabidopsis thaliana, and functional and molecular comparisons between AS2 and other family members. Plant J. 58, 525–537 (2009).
[8] Nogueira FT, Madi S, Chitwood DH, Juarez MT, Timmermans MC. Two small regulatory RNAs establish opposing fates of a developmental axis. Genes Dev. 21, 750–755 (2007).
[9] Pekker I, Alvarez JP, Eshed Y. Auxin response factors mediate Arabidopsis organ asymmetry via modulation of KANADI activity. Plant Cell 17, 2899–2910 (2005).
[10] Kerstetter RA, Bollman K, Taylor RA, Bomblies K, Poethig RS. KANADI regulates organ polarity in Arabidopsis. Nature 411, 706–709 (2001).
[11] Schneeberger RG, Becraft PW, Hake S, Freeling M. Ectopic expression of the knox homeo box gene rough sheath1 alters cell fate in the maize leaf. Genes Dev. 9, 2292–2304 (1995).
[12] Tsuda K, Hake S. Diverse functions of KNOX transcription factors in the diploid body plan of plants. Curr. Opin. Plant Biol. 27, 91–96 (2015).
[13] Y Yu C, Yan C, Liu Y, Liu Y, Jia Y, Lavelle D, An G, Zhang W, Zhang L, Han R, Larkin RM, Chen J, Michelmore RW, Kuang H. Upregulation of a KN1 homolog by transposon insertion promotes leafy head development in lettuce. PNAS 117(52) (2020).